Cardboard does not belong on your soil. Period.

In the quarter century that I’ve been researching, publishing, and educating on the topic of landscape mulches, one thing has become clear: cardboard should never be used as a mulch. This viewpoint has been of great interest to gardeners; in fact, my earlier post has been the most frequently viewed post since it was published in 2015. I occasionally appended new information to the original post as needed, but the topic deserves an update.

Landscape mulching with cardboard is wildly popular but has no published research to support it. Photo courtesy of Chris Martin on Flickr.

Rather than rehashing what’s been written earlier (which can be found here, here, here, here, and here in addition to the link above), I’m providing information in a Q&A format that might be helpful:

Q: Is there research on using cardboard mulch in home landscapes?

A: Not much. To date, the only peer-reviewed research relevant to landscape soil conditions is our own work published in 2019. The abstract explains the importance of the results to landscape soil health as stated in the abstract (below):

“The orders of magnitude differences in diffusion coefficients among the mulch materials, however, could negatively impact a diverse soil environment such as those found in biologically rich landscapes with higher oxygen demands. Among the mulches tested, wood chips are a preferred method of mulching in terms of providing best gas permeability, particularly in landscape conditions.”

This chart (derived from our 2019 study results) demonstrates the increased impairment of gas movement by different mulch types.

Q: Cardboard has been used as a mulch in agricultural production. Why doesn’t that research support using it in landscapes?

Sheet mulches, including black plastic, is frequently used in agricultural production where weed control and maximzing plant yield are the most important concerns. Photo courtesy of Wyoming BLM.

A: The goal in agricultural production is to maximize yield of an annual crop. In contrast, the goal in caring for a permanent landscape is to maintain a healthy soil ecosystem that will support plant life long term. The table below explains these differences in more detail.

Comparative criteria for intensive agricultural production, home vegetable gardens, and managed landscapes

Q: Okay, I understand that science doesn’t support using cardboard as a landscape mulch, but what about my vegetable garden? Isn’t the research on agricultural crops relevant there?

A: The research on agricultural production mulches is more relevant if maximizing yield is your most important goal. But your goals may include maintaining a healthy soil ecosystem, reducing the use of pesticides and fertilizers, and other criteria. Are you concerned about the established negative impacts that cardboard and other sheet mulches have on soil life? If so, then sheet mulches are not a good choice compared to chunky, three-dimensional mulches.

Q: I like reusing cardboard packaging as part of organic weed control. Isn’t that a good enough reason to use cardboard?

A: In addition to interfering with water and gas movement into the soil environment, corrugated cardboard has chemical contaminants that you really don’t want in your soil or even your compost pile. Corrugated cardboard contains environmental contaminants including dioxin and PFAs or “forever chemicals.” No gardener should want to introduce more of these widespread contaminants into their landscape or garden soils.

Recent peer-reviewed publication looking at hazardous chemicals contained in cardboard and other recycled materials.
Table from Fernandes et al. (2023). Compare the levels of contaminants between shredded cardboard and untreated wood shavings.

As I’ve been recommending for nearly a quarter century now, the very best mulch to use for treed landscapes is arborist wood chips. There is robust, peer-reviewed science establishing the benefits of arborist chip mulches in controlling weeds, enhancing growth and establishment of landscape plants, and maintaining a functional soil ecosystem. In contrast, sheet mulches such as plastic, weed fabric, and cardboard have demonstrated negative impacts on the long-term health of landscape soils. Any resource that says otherwise is not paying attention to the research-based facts.

Arborist wood chips protect exposed soil and suppress weeds while supporting desired landscape plants

The Times They Are A-Changin’—What the new La Niña Watch means for the NH growing season

In this blog I’ve talked several times about El Niño and La Niña and how they affect climate across the Northern Hemisphere as well as their impacts on the rest of the world. We are currently in a strong El Niño with sea surface temperatures in the Eastern Pacific Ocean (EPO) that are much warmer than the long-term average. But underneath the surface the ocean currents are starting to change and the El Niño is expected to swing quickly into the opposite phase, La Niña. That will affect us in North America but also other parts of the world since both El Niño and La Niña are linked to global atmospheric patterns. Since a La Niña Watch was just issued by NOAA this week I will be talking about the changes we can expect to see over the next few months and how those changes will affect gardens and gardeners.

Daffodil crop ready, Andrew Wood , Commons Wikimedia

Review—What are El Niño and La Niña?

El Niño and La Niña are opposite phases of a large-scale atmosphere/ocean pattern that is driven by temperatures in the EPO. The pattern affects climate in many places around the globe. It is the biggest driver of seasonal climate in the Southeast and Pacific Northwest as well as in some other countries, especially in Northern Hemisphere (NH) winter when it is usually the strongest.

In September 2023 I discussed the likely impacts of the El Niño that was growing at that time and how it would affect your winter gardens. The conditions I expected have mostly been observed, although there are some local differences that are not surprising considering that each event is unique. Northern states have been incredibly warm with little snow, while in the Southeast we have had a lot of rain and cooler (although not frigid) temperatures due to wet soils and a lot of clouds blocking the sun. California is getting hit by one atmospheric river event after another, so they are also very wet and are even seeing a lake in Death Valley. I imagine they will have quite a bloom of spring flowers when it gets warmer because of the ample moisture. What have you experienced in your area? Did my earlier column get it right?

Alnarp (Sweden)—Spring Leaves, Susanne Nilsson, Commons Wikimedia

How is this season different than a typical El Niño winter?

Even though we have had the swings of El Niño and La Niña (collectively called El Nino Southern Oscillation or ENSO) for thousands of years as evidenced by layers in ice sheets in Peru and ocean sediments, there are other changes that are not cyclical. The rise in global temperature over time is showing up as a warming trend in all seasons but especially in winter. That does not mean we don’t see other swings in climate over time because ENSO and other atmospheric cycles are still occurring, but they are superimposed on the slowly rising temperature associated with increases in greenhouse gases so the cold outbreaks aren’t quite as severe and the warm spells last longer.

Sea surface temperature departure from normal for 2024-2-12.

This year one of the most notable things we are seeing in global climate is the unbelievable warmth in the Atlantic Ocean. Temperatures there now are at values consistent with June or July temperatures! This is the energy that will feed tropical storms later in summer (more on that in a minute). Scientists are still not sure of all of the factors that are contributing to these record-setting conditions, but they may include the eruption of Hunga Tonga, the elimination of sulfur emissions from modern cargo ships, and changes in the global ocean circulation.

Plum blossoms starting to bloom, John Morgan, Commons Wikimedia.

In addition, in spite of one cold big outbreak this winter across the eastern United States, most areas have been warmer than normal resulting in an early spring that has brought honeysuckle leaves to my yard more than a week early. You can follow the “green wave” north and see when it gets to your area or verify that it’s already there at the National Phenology Network site. I am concerned about the possibility of having another late frost like 2023 that could impact the peach and blueberry growers in the Southeast since our average last spring frost date is early to mid-March for most of the commercial peach region. There has been enough cold weather for most of the fruit-producing plants to have reached their required number of chill hours, which means the warm weather is making them ready to bloom. While I don’t see another cold outbreak on the horizon for the next few weeks, we have had frosts in the Southeast into April before so we are not out of the woods yet.

ENSO probabilities for 2024 as of mid-February.

When will La Niña begin?

Climatologists predict that El Niño will weaken through spring and we will swing back into neutral conditions by the April through June period. From there most models predict we will move into a La Niña by the June through August period. By NH fall (September through November) there is a 77% chance we will be in La Niña conditions. This has implications for the summer and especially for the Atlantic tropical season since in neutral and La Niña years the number of tropical storms that occur in the Gulf and Atlantic is higher than in El Niño years. Last year despite El Niño we had 20 named storms, much more than the average of 14 events. This was in part due to the unusually warm water. Most of those stayed over the Atlantic Ocean rather than make landfall due to the presence of a strong jet stream high in the atmosphere which disrupted the development of storms farther to the west and prevented a lot of damage to us in the United States. In spite of that, we still had Hurricane Idalia and Tropical Storm Ophelia, both of which caused a lot of damage to infrastructure and agriculture.

With La Niña fully in place by fall, there will be little to stop the development of tropical storms in the Gulf and Atlantic Ocean except for Saharan dust and unfavorable weather patterns in the United States that could at least shunt any storms away from land. Some early unofficial predictions are for 25 or more named storms to occur this year, although the official predictions are still a few weeks away.

Next winter, we can expect La Niña to control a lot of our climate. That means warmer and drier conditions across the southern part of the United States while cold and wet conditions return to the northern states. Here in the Southeast, that means soil could be pretty dry in spring 2025 leading to issues with planting although it will be easier to drive heavy equipment into the fields than I expect will happen this year.

Field with daffodils, Txllxt TxllxT , Commons Wikimedia

What does all of this mean for gardeners in the United States?

Because of the recent warm conditions associated with rising temperatures and enhanced by El Niño in northern parts of the country, spring is coming early to many places. That can be a good thing if you like flowers and don’t like snow, but it does mean that your early flowers will still be susceptible to frost damage if we get another cold outbreak later in March or even into April or May for northern states. So you will need to be prepared to protect the tender plants if a frost or freeze occurs.

The end of El Niño and the eventual rise of La Niña also has implications for areas that are affected by tropical systems. This includes the Gulf and East Coasts and areas downwind of those locations but can also include parts of California and the Southwest which can see impacts from tropical systems in the EPO west of Mexico. Rainfall could be hit or miss in the late summer depending on where the storms go. You should prepare well in advance of June 1, the official start of the season, because the warm ocean water could allow tropical storms to develop in May ahead of the “official” start. That means making sure you remove damaged limbs or other objects that could become wind-borne debris, make sure you have adequate drainage for heavy rain, and keep an inventory of your belongings that could be washed or blown away in a storm. Have a family plan to keep in touch and evacuate if you need to, including pets and livestock. You can find a lot of good information on preparing for and recovering from natural disasters in this University of Georgia handbook, even if you are not in Georgia or the Southeast.

Forsythia in snow, Famartin , Commons Wikimedia

While the current warm weather makes gardeners eager to get out in their plots and get started, it’s probably too early to start in most of the country except the most southern areas. But you can dream and start planning for the warmer weather soon to come!

Unpacking a Peck of Purple Genetically Engineered Tomatoes

Excitement spread across social media recently with the announcement that a genetically engineered tomato, creatively named “The Purple Tomato” is now available for home gardeners. Gardeners, plant scientists, and others rejoiced at the news that a purple tomato engineered with genes from a snapdragon to boost the plant pigment anthocyanin is now available for home gardeners to purchase. But why were people so excited? And what does this mean?

The Purple Tomato: What is it and why is it exciting and important?

The Purple Tomato was developed by a company called Norfolk Healthy Produce. The company was founded by Professor Cathie Martin (and other scientists) who is a professor at the University of East Anglia and a group leader at the John Innes Centre in the UK. On February 6, 2024 they announced that seeds were available to home gardeners in the US after clearing regulatory approval hurdles by the USDA, EPA, and FDA to assure that it is safe for human consumption, for growth in US without safety containment measures, and that it does meet its claims of added nutrients. Read more about the US regulatory process here.

For all the tomato aficionados out there, The Purple Tomato is an indeterminate cherry tomato. Indeterminate means that the plant doesn’t stop growing as long as it is healthy and will produce a “vine” that needs to be staked or trellised off the ground. Production of fruits continues throughout the season starting at the bottom of the plant and going up as long as it is healthy.  Of course, it is a cherry tomato so you’ll have hundreds or thousands of tiny fruits to pick through the season. Some gardeners love growing cherry tomatoes. Others hate it for that fact. So you win some, you lose some.

Read more on indeterminate vs. determinate here.

The tomato contains two genes from snapdragon flowers that boost anthocyanin production in the tomatoes. Anthocyanins are the plant pigments responsible for blue and blue-purple colors in plants. And they are shared across all plants with these blue and blue-purple colors, so the addition of purple pigments from a flower isn’t too out of the ordinary since tomatoes already contain similar pigments. (The reddish violet/crimson color of plants in the Amaranthaceae family (beets, amaranth, chard) are from betalin pigments, not anthocyanins, FYI.) Most plant pigments actually have the added bonus of also being highly beneficial for human health as most of them are antioxidants and have other health benefits. The incorporation of anthocyanins boost the nutrient quality of tomato since anthocyanins are considered strong antioxidants. Studies also implicate anthocyanins in reducing blood pressure and heart disease, preventing neurological disease, and slowing cancer growth due to the reduction of free radicals that can damage DNA.

Source: Overview of Plant Pigments, Springer

Now, anthocyanins in tomatoes are not new. Many hybrid and heirloom varieties of tomatoes contain anthocyanins. The tomatoes that already contain anthocyanins are the tomatoes that are often considered “purple” or “black” by seed companies and home gardeners. Like ‘Cherokee Purple’, ‘Black Beauty’, and ‘Black Krim’. However, the anthocyanins in these tomatoes are generally found in low quantities as they are only found in the skin and or the flesh just under the skin. What makes “The Purple Tomato” novel is that it is the only tomato that has the anthocyanin pigment in both the skin and throughout the tomato. Seeing pictures of the tomato, the vibrant purple color goes through the entire tomato and is striking. (It also doesn’t hurt that purple is my favorite color). Due to this purple color throughout the tomato, the fruits have a much higher concentration of anthocyanins than existing cultivars.

Another thing that excites me about The Purple Tomato is that the company claims that is an inbred/open pollinated variety. Meaning that home gardeners can save the seeds from year to year and the anthocyanin traits will continue to be present. This also signals a departure from normal genetically engineered seeds where the traits aren’t as persistent and seed saving isn’t allowed. The company does have some terms and conditions about not selling seeds (from the ones you buy or likely from any you save) and not using them to breed other varieties. But gardeners are free to save seeds and share fruits, plants, and seeds with your local community.

“GMOs” and home gardening

Despite what many people may think, until the release of this tomato there really weren’t any genetically engineered plants available to home gardeners. This marks the first time that a plant has received approval from the US government agencies that control the release of genetically engineered plant for sales directly to home gardeners. Most of the genetically engineered plants have been developed for and are available only to commodity crop (corn, soy, cotton, etc.) and select horticultural crop (papaya, some select squashes, and now Arctic apple) farmers. There’s a highly regulated process and contract procedure for farmers to obtain the seeds or plants that just isn’t practical or cost-effective for the plant developers to market to or make seeds for home gardeners.

Source: UC Davis Biotechnology Program

We’ve written several times about how, until now, there really hasn’t been genetically engineered seeds available to home gardeners, despite what some seed companies would have you believe (here and here). There has unfortunately been a lot of confusion for home gardeners thanks to misguided and/or deceptive marketing practices by certain (heirloom) seed companies that labeled their “Non-GMO certified” seeds and preached about the dangers of genetic engineering to sell more of their seeds even though there have not (until now) been any “GMO” seeds available for companies to even sell to home gardeners. Unfortunately that deceptive marketing created enough fear and fervor that most seed companies had to start labeling their seeds “Non-GMO” just to preserve their sales and cut down on harassment from folks on social media trying to “call them out” for selling GMO seeds.

Not until the release of “The Purple Tomato” has there been a home garden seed that could be labeled “GMO” and warrant companies needing to label something as non-GMO. But still it is only one plant, so is it really necessary? Or is it just a marketing tactic?

Purple Tomato Reception

In cruising through the comment section on articles discussing the new tomato, I’ve been pleasantly surprised to see the positive response that it is receiving from the public. There are lots of comments excited about the prospect of a nutrient-dense genetically engineered crop, lots of excitement about buying the seed, and even excitement about the super purple color of the tomato. The few negative comments about GMOs being “bad” have gotten a lot of pushback. I don’t think this would have happened 5 or 10 years ago.

Of course, some of the pushback is a little misguided. Statements like “all plants are GMO” show a similar lack of understanding of what is actually happening, even though it is offered in good faith. Yes, humanity has guided and shaped the genetics of all of the plants we eat over the centuries and many plants have therefore been “genetically modified” by humans. But genetic engineering is a more rigorous and scientific process. This is also one of the reasons why scientists and government agencies prefer the term “genetically engineered” or “bioengineered” to GMO or genetically modified to clear up confusion.

It does seem like the tide has shifted on public acceptance of genetic engineering where until recently many people viewed the technology with skepticism and fear, thanks mainly to misunderstanding and marketing.

Much of the fear and distrust of genetically engineered plants have been around the addition of genes to make crops resistant to certain herbicides, to produce natural immunity to insects, and other traits to increase yields. Many have wrongly assumed or claimed that this has resulted in increased application of herbicides. While application of some herbicides like glyphosate has increased, it has been at the reduction of much more dangerous herbicides. These crops have often been developed and controlled by large chemical companies that, perhaps not totally incorrectly, the general public distrusts. Plus, unintended consequences like herbicide resistant weeds have caused issues.

But the new Purple Tomato goes beyond this and I think is applauded for many reasons. One – it was made solely to boost nutrition. While there have been previous (mostly unsuccessful) efforts to do this in crops (see the story of Golden Rice), this is really the first time it has been aimed at home gardeners. Two – it isn’t one of those “big scary corporations” doing it. It is a company started by academics to promote plant science and health. Three – while the plants are patented, there aren’t strict and secretive agreements against seed saving and sharing. And four – the express purpose of the plant is to increase the healthy qualities of the plant.

In conclusion

It seems like many people are excited about this new genetically engineered tomato on the market. I know that I am. It seems like the public at large is accepting and excited by this new health-boosted tomato and the technology used to make it.

I know I’ve ordered my seeds, and many others have as well. The seeds aren’t cheap, $20 for 10, but the process to make them isn’t cheap either. I’m looking forward to trying them out in my own garden.

Disclaimer: No payment or reward was received for this article promoting the Purple Tomato and I have no affiliation with the company. Norfolk Healthy Produce didn’t even know it was being written. They probably don’t even know who the Garden Professors are and they definitely don’t know who I am. That being said, if they want to reach out with some free seeds or swag, I wouldn’t be mad at them.

Does Wind Chill Affect Plants?

Over the course of this winter there have been several days when the temperature plummeted after the passage of an Arctic front as strong winds blew frigid air into parts of the United States. It can happen in other parts of the world, too. When this happens, the National Weather Service (NWS) often issues Wind Chill Warnings urging people to bundle up before they head outside into the dangerously cold weather. From time to time I am asked if plants also experience wind chill. This week let’s explore how wind does and does not affect plants.

Birch trees in heavy wind and snow in Hemsedal, Norway, Havardtl, Commons Wikimedia.

What is wind chill?

The Oxford Dictionary defines wind chill as “the cooling effect of wind blowing on a surface”. That is partially correct as a general statement of how the wind makes you feel, but it is lacking as a scientific definition. A better one is “a quantity expressing the effective lowering of the air temperature caused by the wind, especially as affecting the rate of heat loss from an object or human body or as perceived by an exposed person.” The wind-chill index is a calculated index that tries to quantify how a strong wind can remove heat from a human or animal body. A low wind chill indicates that heat is being rapidly removed from the body, potentially resulting in the lowering of internal temperature and the chance of frostbite to extremities like fingers, toes, and noses if directly exposed to the frigid wind.

“Wind chill” is used by the NWS as a way to provide a warning message to people who might be working or playing outside to make sure they are well protected from direct contact with the wind. As a calculated index wind chill cannot be measured directly although there have been some lab experiments in temperature-controlled laboratories that have tried. The formula for calculating wind chill has been changed in the past as science has improved our understanding heat transfer by wind.

Source: RicHard-59, Commons Wikimedia.

How does wind chill work?

When wind blows across a surface, it causes a transfer of energy between the wind, which is at one temperature, to or from the surface which is most likely at a different temperature. If the temperature of the wind is lower than the surface, then heat (which is just a measure of the energy of the molecules at the surface) is stripped from the surface and transferred to the wind. That lowers the energy of the surface and cools it off (note that this is different than evaporative cooling, which is cooling due to evaporation of water from a surface). The faster the wind blows, the quicker the energy is stripped away. In summer, when the ambient air temperature is high, this cooling effect from a breeze off a cooler water body like the ocean may feel pretty good. But in winter, when temperatures are already icy, it may cool off the surface (and by connection, the body beneath the surface) to dangerous levels resulting in frozen cells that are the hallmark of frostbite or hypothermia if the core body temperature is affected.

Trees on the ridge, Gael Varoquaux from Paris, France, Commons Wikimedia

Plants do not generate internal heat and so are generally the same temperature as the air. Because of this, there is no transfer of heat energy between the air and the plants and so the plants would not experience “wind chill.” However, anything that has an internal source of energy, including humans, animals or running engines, could experience a chilling effect as heat is stripped away from the surface by the wind especially if the warm surface is exposed directly to the cold wind. That is why it is important to wear layers to provide protection from the wind when the wind chill is expected to be extreme since it keeps heat from being removed from the skin. Ranchers help protect their livestock in blizzards by creating wind breaks that reduce the wind speed and so limit the impacts of wind chill on their cattle. Newborn calves may be especially susceptible to wind chill on their ears and may be outfitted with earmuffs to protect them from frostbite.

A calf wears adjustable ear muffs called Moo Muffs to protect its ears from frostbite. (WPR Photo courtesy of Holly Poad), published in the Superior Telegram on January 23, 2020.

What other impacts does wind have on plants?

Even though plants do not experience wind chill, that does not mean that there are no impacts from the wind. In addition to transferring heat, wind can also transfer moisture from the plant to the air, desiccating the plants if the humidity of the air is low. This can happen at any temperature as long as there is not much water vapor in the air, but we generally think of it happening at high temperatures because the difference between the water content of the plants is much higher than the water vapor in the air. The difference in humidity, like the difference in temperatures, leads to transfer of water out of the plant and into the air blowing over it. It’s not all bad, though–wind blowing through the plant canopy can be a good thing if it keeps humidity levels near the plant low enough to prevent the development of fungal diseases that thrive on very moist conditions, so gardeners should consider wind conditions in their garden when they determine where to place their plants and what to grow.

Winds can also cause damage to trees and garden plants. I recently read an article that indicated nearly all tree trunks break at the same wind speed of around 90 mph (42 m/s), regardless of species or size. According to the authors, “In a strong wind, a tree may break through one of three mechanisms. Uprooting can occur in rain-moistened ground, or if the tree’s roots are rotten. Alternatively, if the roots can hold, then it becomes the tree trunk that is at risk from breakage – either through torsion or, more commonly, bending.” Of course, damage to tree limbs can cause breakage at weak spots as well at lower wind speeds.

Bent over with the wind (Isle of Wight), Ronald Saunders from Warrington, UK, Commons Wikimedia.

Wind also has beneficial impacts on plants. The gusty nature of wind causes variable forces on tree trunks and plant stems that increase their strength by forcing them to resist the wind. That is one reason why you might not want to stake young trees too tightly, because they need to be able to move in the wind to form strong tapered trunks. Wind that blows all the time in the same direction causes trees and plants to grow in distorted (and sometimes beautiful) ways as their shapes are formed by those constant winds. Wind also provides a way to spread pollen from one tree to another, helping to spread genetic material through a wide area for reproduction.

Pine (Pinus sylvestris) releasing pollen into the wind in Tuntorp, Brastad, Lysekil Municipality, Sweden.

If you are interested in reading more about how wind affects gardens, check out my earlier blog post at

Putting down a danger tree

I’ve been a gardening mythbuster for almost a quarter century. You’d think the quality of information would slowly be improving, given the increased sophistication of many gardeners regarding their information source. But every day my news feed connects me with articles that I’m sure some AI entity thinks will be enlightening. One recent story getting lots of eyeballs is entitled “The Benefits of Girdling a Tree Vs. Cutting It Down.” It makes for a good application of the CRAP analysis. While the link to the publication I’ve provided will go into more detail on CRAP analysis, all you need to know for this post is we’re going to assess Credibility, Relevance, Accuracy, and Purpose of the information.

Urban trees whose roots have been severely pruned should be removed to minimize the risk of failure.

First, let’s consider the Credibility of the source. According to, the author is “a plant mom…intrigued by nature and plant life which she exhibits by caring for and doting on her succulents.” Her college degree was in applied biochemistry, which has no substantial connection to applied plant and soil sciences. Bottom line, the author is not an expert in the science of tree care.

Let’s look at Accuracy next (we’ll get to relevance later). The author’s premise that girdling is “another great option” for tree management is grossly inaccurate. The article contains no links to any published research supporting her opinions, and demonstrates a lack of understanding woody plant physiology. The author states that girdling “would prevent erosion from occurring” in contrast to cutting the tree down which apparently removes “the tree roots acting as a protective cover for the soil.” Cutting a tree down removes its crown, but leaves the root system undisturbed. The roots stop transporting water aboveground (there’s no demand for it any longer) thought they can continue to grow as long as they have stored resources. Eventually they will die and their woody structure slowly decomposes.

Erosion’s going to happen any time you have unprotected soil: roots aren’t a “protective covering” (but mulch is)

Girdling the tree, on the other hand, does not prevent root uptake and transport of water through the xylem to the crown of the tree. It does prevent phloem movement of sugars and other resources from the crown to the roots. In other words, roots remain active in transporting water and nutrients but slowly starve to death without phloem-transported sugars and other resources. A good article on the topic of tree girdling goes into more physiological detail on the process that causes trees to decline “before entering an irreversible state of desiccation caused by definitive root death.”

Another possibility is that the girdled tree might send up new shoots below the girdling, leading to the formation of a new crown. Without constant vigilance in removing these new branches, the tree will survive and presumably continue to cause whatever problems that led to the original mismanagement.

The author also suggests that girdling is useful in preventing disease spread: “A sick tree would need to be killed in order to prevent the disease from spreading out to other trees and vegetation.” Or, if your trees “are hoarders by nature,” girdling renders them “incapable of taking in nutrients and being a burden to the environment.” Neither of these statements is accurate.

Trees on farmland provide a number of benefits, and the risk to people and property is far lower compared to residential areas.

While the information in this article is somewhat Relevant to homeowners, it does wander into agricultural advice. We’re advised if we have “a danger tree or one that is resting on arable farmland with crops on it, it’s strongly advised that you chop it down and not girdle it. You don’t want an unpredictable girdled tree falling on your harvest, house, or worse — on someone — out of nowhere.”

At this point it’s worth noting that deliberately killing a tree by girdling also opens the property owner up to legal action should the tree fall and damage property or injure someone. This alone should be enough to dissuade property owners from taking advice from this article. And given the number of years it can take for a girdled tree to die (and eventually fall), is this really a useful process if you need to have a tree removed for some reason?

Finally, what is the Purpose of this article? It’s hard to know exactly why the author promotes girdling, and the language she uses in describing tree care is odd. Statements such as “sometimes circumstances call for trees to be put down and killed” and “trees need to be put down for all kinds of reasons” seem to equate trees with stray animals or dangerous wildlife. It creates an antagonistic situation where none exists.

Tree management, especially when it come to discussions about removal, needs to involve a certified arborist who can assess potential risks associated with leaving, as well as removing, any tree.

Shoveling the Artificial CRAP: Navigating Gardening Un-Intelligence in the age of AI

Like it or not, the use of AI (Artificial Intelligence) has become a part of our daily lives. While you might not use AI directly (or you don’t know that you do) it is now a common part of society, especially in the online world. Many people, sites, can companies use it to create content. It is part of the “smart” gadgets that we use at home. Map software (like Google Maps), search engines, ride share apps, and even the spam filter on your email all use AI. You’re even more likely to encounter AI on social media and even standard media these days, with it being used to write articles and text, create ads, and images.

We know that there’s no getting around it these days. You’ve probably heard stories about how AI provides incorrect information, steals content, or might help the robots overthrow humanity today. While it seems to be the wild, wild west, there are a few (voluntary) safeguards in place now to prevent the overthrow of humanity (I hope).  Where the real damage is right now is the use of AI to mislead people outright. There’s also some danger from just lazy use of AI where whoever is using it to create content just copies and pastes it verbatim without checking what it actually says.

Gardening misinformation on the internet is nothing new. Gardening misinformation before the internet is nothing new either. But the risk that AI poses is the amplification and multiplication of that information. It is now easier than ever for someone to create online content at the click of a button. And the way that AI works is it scours the internet for existing information to learn how to respond. This new(ish) generation of AI is generative, meaning that it can actually put together information to form something new. Previously, if you did an internet search you would just get a list of websites to read for information. Now AI can use those sites as source material and write the information in a new way – however you prompt it to do. Search engines like Microsoft’s Bing (the much-loathed replacement for the archaic Internet “Exploder”) now have AI built in as a feature. AI is only as smart as what it can learn on the internet, and we all know that while there is good information on the web it is also full of a lot of manure.

Identifying Artificial Gardening Information

First, how can you tell if it is AI generated?  At first glance you might not be able to tell. It is just like any writing. There are tools you can use to try to figure it out, but you’ll often find that writing from AI doesn’t have personality. It is often very dry. You can tell it to add humor or any other style to its writing, but it often misses the mark. When I asked ChatGPT (one of the common AI platforms) to add humor to something it sounded like I was trying to be cutesy, like an employee at the famous park in the swamps of Orlando run by a mouse and not my usual wit, sarcasm, and cynicism. AI often fails to see context and answers are often very black and white. Which doesn’t work in dynamic systems like gardening and the environment. AI therefore sticks a lot with generalities and doesn’t often provide a lot of specific information unless you ask for it.

As an example, I prompted ChatGPT to write “three sentences about seed starting”. Here’s what it spit out:

1.Starting seeds is a crucial and exciting step in the gardening journey, allowing individuals to cultivate a diverse range of plants from the very beginning.
To initiate successful seed germination, it's essential to provide the right conditions, including proper soil moisture, adequate light, and appropriate temperatures tailored to the specific needs of each plant variety.
Patience is key when starting seeds, as the process requires careful monitoring and nurturing until the seedlings are strong and ready for transplantation into the garden or larger containers.

Nothing alarming there, but it is pretty dry and isn’t very informative. It isn’t what I would write. Now, I prompted it to rewrite those sentences, but to add “humor and wit”. This is what it vomited out:

Embarking on the seed-starting adventure is like launching a tiny plant spaceship into the garden galaxy – a small step for seeds, a giant leap for your green ambitions!
Think of starting seeds as playing matchmaker for your plants, introducing them to the perfect conditions for a successful germination romance – a cozy soil bed, a flirtation with sunlight, and a temperature that says, "I'm hot for you, seedlings!"
Growing plants from seeds is a bit like raising the green equivalent of toddlers – they demand attention, throw tantrums if the conditions aren't just right, and you'll find yourself wondering if they've developed personalities before you know it!

Vomit, indeed. Though still nothing too alarming. Definitely too cute and not enough snark.

Where AI generated text falls short is that it incorporates some of that incorrect manure from the web in answers. It doesn’t know that information on the web is incorrect. A few times it told me to put rocks in the bottom of pots for drainage (something we’ve fiercely disproven time and time again).

It told me to practice companion planting (another fallacy we’ve taken on) but it never gave me a lot of details about how to do it.

I did ask it directly about biodynamic gardening, which is the pinnacle of garden misinformation. It gave an amazingly nuanced and diplomatic response, which is much closer to what I’d actually say and much nicer than what GP founder Dr. Linda Chalker-Scott would say. (Don’t tell her I said that).

“Biodynamic gardening is a holistic approach that considers the interconnectedness of plants, animals, and the environment. While some gardeners find it beneficial for promoting sustainability and soil health, its importance depends on individual preferences and beliefs. Biodynamic practices often involve using lunar cycles and special preparations. If you value a holistic and spiritual approach to gardening, incorporating biodynamic principles might align with your preferences. However, it's not essential for every gardener, and many successful gardens thrive with conventional organic practices.”

So, nothing too earth shattering in text, but where I think the real risk lies is in AI generated images and videos. It is easier than ever to create images of things that aren’t possible or incorrect and pass them off as real. People often do this to drive traffic – by making wild claims that people must check out or by “rage baiting” people who just have to respond to tell people how wrong something is (it still drives engagement and earns money). 

Fake images are nothing new in the gardening world. I can’t tell you how many ads I’ve seen for magical rainbow-colored rose seeds, trees that grow 10 kinds of fruits, and more all before the advent of AI. But now it is easier than ever to create those images at the click of a button.

For an example, I turned to DALL-E, which is a common AI Image generator. I tried to think of things that wouldn’t be possible. My first prompt was “monarch butterfly on a snow-covered flower”. Something that isn’t possible, but that someone might create to make a social media post about something amazing or miraculous that people have to see to believe.

The results look realistic(is) enough, though improbable. But you’d have to know that to not believe it.

Image generated using DALL-E with prompt: monarch butterfly on a snow covered flower

The second test, not so much: “realistic looking tree that has 15 different types of fruits and veggies growing on it”. I had to add the “realistic” because the first results were cartoon-y. It didn’t help much. So, I guess my magical 15 fruit and veggie tree won’t be coming to an online scam shop any time soon.

Image generated using DALL-E with prompt: realistic looking tree that has 15 different types of fruits and veggies growing on it

So, I moved on and created “a grape vine covered with scary looking bugs”.

Image generated with DALL-E with prompt: a grape vine covered with scary looking bugs

At first glance, the result can look terrifying. But if you inspect it closely, you’ll see that those bugs have all kinds of legs coming from all over their bodies. Scary, yes, but realistic – no. But could someone do something like this to scare people about an invading insect? Absolutely!

Cutting through the Artificial CRAP

GP Founder Dr. Linda C-S has written about using the CRAP test to identify if a source of information is trustworthy. She used it to talk about Jerry Baker, the self-appointed “America’s Master Gardener” who peddled misinformation and garden snake-oil for decades through books and tv shows to earn big bucks. The same principles can be applied now to digital content created by AI to help figure out if the information is reliable. Here are the steps:

C = credibility. What are the credentials of the person or organization presenting the information? Are they actual experts? Or is it a random account that doesn’t have ties to a credible source? Does the source have academic training, or even practical knowledge?

R = relevant. Is the information relevant for home gardeners? Or does it try to use information other than home gardening, like production agriculture, to answer the questions. For AI, especially images, I could also say that R= realistic. Is it something that could actually be true, or is it a monarch butterfly covered in snow?

A = accuracy. This could lend itself to the realistic assertion, but I see this as more in accuracy of the source of information. Does it site sources, like journal articles, extension publications, USDA reports, etc.? And does the information follow along with trusted information from other sources?

P = purpose. Why is someone presenting this information? In the Jerry Baker example, he was raking in money with books, TV shows, and product promotions. But what benefit does someone get from posting incorrect info on the web? Also, money. Whether you give them a dime, most social media sites and websites generate income by the number of clicks or viewers they have. How do you think people get rich and famous from TikTok? People aren’t paying them to watch them, but they generate income from engagement and interaction. So, creating content that is fanciful to get people to check it out, or even wrong for people to interact with it to rail against it, creates income.

Is all AI bad?

Not necessarily. I mean, the technology is applied in so many ways to solve so many problems. Sure, there is a risk and people do misuse it. But AI can be a powerful and useful tool when used appropriately, when information is checked, and when it isn’t copied and pasted directly. For example. Over most of 2023 I wrote a series of GP articles about plant diseases. No, I didn’t have AI write the article. That would have been wrong. But I did ask my friend ChatGPT to create lists of common diseases for each type of disease to write about. Instead of me having to dig through social media to see what people were asking about, the platform searched to see what the most common diseases that people talked or asked about were, or which ones were most likely to show up on websites. But I took that list, added to it, subtracted from it, and then wrote the article myself. But the more unethical (and lazy) users of AI just copy what it says verbatim without even reading or editing for accuracy. Or even have automated systems that just crank out AI-generated content with no oversight.

In the end, AI isn’t going away. So as savvy gardeners we just have to know what to look for to “spot the bot”.  And always be ready with a shovel to scoop away the CRAP.

Winter Thoughts in Support for Fallen Leaves

January is here with its resolutions, cold long nights and not that warm days. Winter is a season of rest and survival. The cats and horses have long furry coats, the resident song birds eagerly clean out the feeder every day and the garden beckons. For me Winter is a special season when I can do a lot of fruit tree pruning, especially enjoyed with my daughter. Father-daughter pruning bonding is not to be missed if it’s an option for you. Gardens are tuned to winter as period of rest but the promise of longer days that will initiate the changes that happen in Spring will soon be upon us. In this post I’ll reflect on how plants survive winter and what we can do to help them.

Winter is actually a very dry time of the year in many places and the winter cold that freezes soil leads to dehydration. Plants installed just before winter will not emerge in spring alive w/o moisture in their systems. Mulch is an essential and natural part of winterization for many North American temperate plants. Protecting the root ball of a newly planted perennial is a must do for winter survival. In nature this is accommodated by the deciduous habit of many trees and shrubs, falling leaves are a big part of winterization. In our gardens we can do this with mulch.


I know deciduosity is not often used but I like to use unusual words so here we go. The deciduous habits of many north American temperate trees enable them and other plants to survive cold, dry, freezing winters. Environmental cues (photoperiod and cooling temperatures) signal trees to drop their leaves (Fadon et al., 2020). Cold temperatures are also required by temperate perennials to invigorate buds and make starch into soluble sugars for strong spring growth. Deciduosity also leads to abundant mulch on the forest (or garden) floor. This protects soil and surface root systems, seeds, perennial herbaceous plants and bulbs and provides an insulating layer under snow, if snow is a thing where you are. When warm temps arrive in Spring the leaves quickly break down as growth under them emerges.

Leaf fall covers the forest floor protecting roots and increasing arthropod diversity in the litter layer.


Deciduosity brings certain challenges to woody perennials that donate their canopy to the soil each year. Trees in spring have no photosynthetic organs to supply the energy of growth. That energy has to be stored in the wood and roots as carbohydrates, mostly as starch, at the end of the growing season and before leaf fall. In spring at the end of dormancy when buds grow, these stored carbohydrates convert to soluble sugars and fuel the rebirth of a a new canopy. Having all that stored sugar in cells throughout the plant also reduces the freezing point of water in the cells so that subzero temperatures do not lead to ice crystal formation (and cell death) of the dormant plant.


Another way plants survive Winter is by forming seeds. The strategy of annual plants is to “go to sleep” as seeds and “wake up” by germinating. To ensure that seeds don’t germinate too early, they often have inhibitors that need to be washed away by water (Spring thaw), burned by fire (usually summer time), or by scarification (tumbling in the creek etc). Many seeds germinate better after a cold winter than if they were sown without cold chilling. Not all seeds will germinate at the same time as inhibitors delay germination. This ensures that conditions will be right for some of the seeds and thus the species will survive, even thrive in the right place.


While the above ground part of gardens can be in a dormant state in January, the situation underground is different. Roots respire (break down sugars to get energy for growth) during winter and may grow continuously depending on climate, depth and soil coverage conditions. Roots, just like buds, utilize stored carbohydrates to fuel their growth. If temperatures remain more moderate under the soil they can continue to respire well into winter months. Soils freeze when they lack snow cover or mulch, Reinmann and Templer (2016) propose that roots in frozen soils are less active. Leaf mulches help protect soils from hard freezes.

Snow cover protect soils from freezing and leads to more live roots during spring emergence from dormancy

Am I crazy or What?

I know that a leaf dump on the garden every year is not what many gardeners want to deal with. That is what leaf blowers are for right? Some municipalities even have line items in their budget for disposing of fallen leaves which are some of the most disposed of green waste. Leaves that accumulate on hardscape can be a pollution source accounting for up to 80% of phosphorus pollution in one study (Bratt et al., 2017). It’s best to utilize leaves around perennials and keep them away from streets, gutters and sidewalks.
Trees evolved to drop their leaves on the ground and for them to stay there. Finding ways to accommodate this in gardens will lead to a healthier garden and less waste in landfills. Leaves can be mown on turf areas and the biomass will be incorporated into the turf sward (Nektarios et al., 1999) without loss of turfgrass quality. In gardens they can become part of the surface mulch. If you are really crazy, you can grind them in a shredder to make really high quality micro mulch to be used around certain plants or vegetables (we do this with coast live oak leaves of which we have an abundance in California). Stavi, (2020) encourages us to think of fallen leaves as a resource not a waste product. Your garden will benefit.

For more information on leaves please see the other blogs at this site:


A. R. Bratt, J.C. Finlay, S. E. Hobbie, B. D. Janke, A. C. Worm, and K.L. Kemmitt 2017. Contribution of Leaf Litter to Nutrient Export during Winter Months in an Urban Residential Watershed. Environ. Sci. & Technol. 6: 3138-3147

Fadon, E. E. Fernandez, H. Behn, and E. Luedeling. 2020. A conceptual Framework for Winter Dormancy in Deciduous trees. Agronomy 10(2), 241;

P. Nektarios, A.M. Petrovic and D. Sender 1999. Tree Leaf Deposition Effects on Kentucky Bluegrass (Poa pratenses L.), J. of Turfgrass Man., 3:(1) 69-74. DOI: 10.1300/J099v03n01_06

Reinmann AB, Templer PH. 2016. Reduced winter snowpack and greater soil frost reduce live root biomass and stimulate radial growth and stem respiration of red maple (Acer rubrum) trees in a mixed-hardwood forest. Ecosystems. 19:129- 141.

Stavi, I. 2020. On-Site Use of Plant Litter and Yard Waste as Mulch in Gardening and Landscaping Systems. Sustainability 12(18), 7521;

The warmest year on record ends–will 2024 be hotter?

This year is almost certain to be the warmest on record for the earth as a whole, although there are still a few days in December that could slightly affect the final numbers. As we close out 2023 I want to spend a few minutes reviewing the weather and climate of the past year, both the average conditions and some of the extremes we saw. While this is skewed towards the United States, I did include some events happening in other parts of the world for our non-US readers. I will also take a peek at what is likely to happen in 2024.

Great Sand Dunes National Park and Preserve, Commons Wikimedia.

What were the average climate conditions in 2023?

Since the year is not quite over I can’t provide a final average for temperature or precipitation for the complete 365 days, but there are some websites that allow me to look at all but the last few days. The images below are from the High Plains Regional Climate Center for January 1 through December 27. They show the temperature departure from normal and the percent of normal precipitation for the continental United States. (You can see the global temperature statistics for January through November 2023 at the National Centers for Environmental Information.) In most parts of the U.S. the temperature was warmer than the 1991-2020 normal; the exception was the western mountains, where temperatures were colder than normal. Keep in mind that the normal period being used for comparison (1991-2020) was a period that was quite a bit warmer than the long-term temperature average in the United States, so this map underestimates how warm this year was compared to most of the 20th century.

Precipitation was more variable than temperature, as it usually is. The driest areas this year were in the southwestern Gulf of Mexico states, particularly Louisiana and Texas, and in the Pacific Northwest.  It’s not surprising that these were also areas with significant droughts, including a lot of the Corn Belt which also saw very dry conditions during the growing season. By comparison, California and New England experienced multiple storms bringing significant rain to those areas, including Tropical Storm Hilary (the first tropical storm to hit California in 84 years) in mid-August. In the Southeast, Hurricane Idalia did almost $5 billion in damage in late August from heavy wind and rain, half of that in Georgia alone. But that did not stop a flash drought from developing there in fall with the almost complete cessation of rainfall for up to 60 days.

What extremes did we see in 2023?

The averages show the overall conditions that occurred this year but don’t begin to capture the extremes in temperature and precipitation that occurred. In the United States alone there have been 25 billion-dollar weather disasters so far this year, including the tropical systems mentioned before along with numerous rounds of severe weather across the country and the devastating firestorm in Maui in August. In other parts of the world, many regions experienced their warmest September-November period since records began in 1880. Significant heat waves occurred in Texas and Mexico as well as Europe, Chile, and Canada, where widespread forest fires that flared up blanketed Canada and many parts of the eastern United States with poor air quality and low visibility in the summer.

Percentage of continental US covered by drought status, ranging from abnormally dry (D0) to exceptional drought (D4) from 2019 to 2023. Source: US National Drought Monitor.

Floods and droughts occurred around the world this year. The Mississippi River dropped to record-low water levels for the second year in a row due to the drought in the Midwest. On the other extreme, notable flood events occurred around the world, include floods in Ghana, the Horn of Africa, Pakistan, Bangladesh, and Chile. Storm Daniel brought unprecedented rain to Libya, breaking dams and causing tremendous damage in September. Nine separate atmospheric river events caused tremendous flooding in California early in the year, significantly reducing drought conditions there and contributing to the reduction in drought area in the United States in the first half of 2023.

While El Niño usually means that the Atlantic tropical season is quiet, this year was unusually active with 20 tropical storms and hurricanes. This is in spite of the presence of a jet stream aloft due to El Niño that usually keeps storms from developing. Most of those storms stayed out to sea, so impacts on the United States were limited (except for Idalia and Hilary out west). In other countries, Hurricane Otis hit western Mexico near Acapulco in October, bringing catastrophic damage to an area that almost never gets hits by tropical storms. Cyclone Lola devastated the northern part of Vanuatu in late October as well.

Monthly global temperature compared with the average for the 20th century. Source: New York Times (link below).

The global temperature will set a new record for warmth in 2023

The New York Times provided a sobering look at monthly temperatures for each month going back to 1850 (above). It shows that 2023 had several months that were the warmest on record for those months, due to the expansive area of warm ocean water associated with El Niño in the Eastern Pacific Ocean along with record-setting sea surface temperatures in the Atlantic that contributed to a very active tropical season in spite of being an El Niño year. The impacts of this warmth are being seen in dropping sea ice coverage, more and stronger heat waves, and increases in wildfires in forested areas. Some people argue that the warming trend appears to be accelerating in recent years, a concern that urges us to consider how we can reduce greenhouse gas emissions and slow down the increasing temperature trend.

What do we know about 2024 so far?

The current El Niño is expected to continue through the next few months before it weakens and turns back to neutral conditions around the April-June period. A La Niña could occur later in 2024, which means that next year’s winter could be warm and dry in southern parts of the Northern Hemisphere and colder and wetter along the northern border of the US and up into Canada. Pending on how long the El Niño lasts, the warm ocean temperatures could contribute to another record-setting warm year in 2024 although it’s too early to be sure. It also depends on shorter-term weather events like more frequent occurrence of cold weather due to a shift in the weather pattern in January to more variable conditions later this winter, as many forecasting models think is likely. Meanwhile, neutral conditions or La Niña conditions later in the year could mean that Atlantic tropical activity increases to an even more active level than last year.

Witchhazel in winter, Si Griffiths, Commons Wikimedia.

Thank you, gardeners, for another great year!

Most of the United States as well as the rest of the world experienced a warmer climate again in 2023, so gardeners will continue to need to choose plants that are appropriate for their warming climate zones. Extreme conditions, including devastation by individual storms as well as natural climate variability, will continue to affect home gardens through water stress caused by drought and extreme heat as well as damage caused by floods, high winds, and freezing temperatures. Building a resilient garden that can withstand these extremes will allow your garden to thrive through whatever conditions the atmosphere throws at it.

I want to end this year by thanking you all again for your loyal readership and your thoughtful questions and comments on many topics. I encourage you to share your 2023 garden challenges (weather or otherwise) in the comments along with your plans for how you plan to address them in 2024 and beyond. I look forward to reading them! We will see you again in the New Year.

Some lists of top weather and climate events for 2023 (mostly videos):

Weather Nation: Looking Back at the Top 10 Weather Events of 2023

Pattrn: 2023: Year of Extremes

NBC News: The biggest climate stories of 2023 Climate Highlights of 2023

Atmos Earth: Your 2023 Climate Wins, Wrapped

Edit this at Structured Data on Commons
Frost in tree shadows, Oswald Bertram , Commons Wikimedia

Plant Disease Primer Part 5: Malicious Misfits

Over the last several months, I’ve covered plant disease basics and discussed plant diseases caused by fungi, bacteria, and viruses. In this fifth and final installment, I’m going to talk about diseases caused by anything but those three different agents. There are a few diseases caused by pathogens that fall outside of those well-known classifications. This list is by no means exhaustive, but it is a good start to show you just what is out there. Where applicable, I’ll be discussing signs and symptoms of the disease, potential control or prevention efforts, and dive a little deeper into describing the actual causal agent. 

First and foremost, some of the diseases I’m sharing might have already been covered in one of my previous installments. The reason for this is that for simplicity’s sake we often lump diseases caused by these “different” pathogens in with a causal agent that they’re similar or related to or evolved from.  It makes describing these things simpler to the general public. But in this chapter, it is my hope to describe and explore just how these things are different as a lesson in how marvelous, interesting, and varied the world is around us.

Phantom Phytoplasmas

Phytoplasmas are single-celled organisms often lumped in with bacteria, seeing as they are actually descended from bacteria. However, phytoplasmas have lost the cell wall that gives bacteria their shape. Phytoplasmas can therefore change shape in response to their environment and to fit in their surroundings better than bacteria which retain shapes like spherical (cocci), rod (bacilli), and spiral (spirilla).

Since they don’t have the protection of a cell wall, phytoplasmas cannot live outside of a host organism and are considered obligate symbiotes. In the case of a plant parasite, it is either the phloem cells of a plant or the gut of an insect vector. Bacteria, on the other hand, are free-living and can exist in the environment and can move between hosts without the aid of a vector insect.

The best known phytoplasma plant diseases are the yellows, with Aster Yellows being the best known. Yellows diseases get their names because plants or plant parts often turn yellow. They become stunted and can develop mis-formed or misshapen parts. Witches brooming, where many twigs, branches, or flowers develop from one point (which can look like a broom) is common. In aster yellows, misshapen and discolored flowers are common. It affects over 300 species, but coneflower, asters, zinnia, and marigolds are common sufferers. In Ash Yellows, ash trees develop unusual leaf growths and witches’ brooms throughout the tree.

Unusual floral growth as a result of aster yellows Source: Douglas/Sarpy Extension – Nebraska

Phytoplasmas require an insect vector, and in the case of yellows, like Aster Yellows, the culprit is a tiny leaf hopper. For Ash Yellows, spittlebugs may also be carriers in addition to leaf hoppers. Since there isn’t a treatment, infection by yellows phytoplasmas can be permanently effective or fatal. The stunting and yellowing will eventually cause a decline in tree health. For herbaceous perennials suffering from Aster Yellows there is no way to revert back to normal blooms. The only way to reduce the likelihood of spread to other plants is removal of whole plants and it can often be too-little-too-late as leafhoppers spread quickly from plant to plant and infection in other plants often occurs prior to noticeable symptoms in nearby origin plants.

Ash tree exhibiting overall decline and witches brooming from Ash Yellows. Source: Missouri Botanical Garden

Vicious Viroids

In part 4 of this series, we discussed plant viruses and how devastating they are to plants. Viroids are also very destructive disease-causing agents and, like viruses, cannot be cured. Viroids are non-living agents, just like viruses, and are even simpler. Where viruses are genetic material (DNA or RNA) surrounded by a protein coat, viroids are just simple strands of pathogenic RNA without a coat. These circular, single-stranded RNA molecules do not encode any proteins and rely on the host cells for replication.

Viroid symptoms include stunting, misshapen growth, leaf abnormalities, and reduced yield. It is possible for some plants to be asymptomatic while being infected and providing a source of viroids to infect other nearby plants.

Viroids can spread to plants in similar ways to viruses, through transmission on dirty tools, propagation from infected plant materials, on seeds, through touch. There is some evidence that viroids can spread through insect vectors like aphids, which is not common for viral diseases. Prevention relies on good sanitation like cleaning tools, planting disease-free and certified cuttings and seeds, and quarantine of new plants that could be infected.

Common viroid diseases include:

Potato Spindle Tuber Disease (PSTVd)

Common Symptoms: stunted growth, deformed potato tubers, yield reduction

Deformed potato tubers with PSTVd. Source: Wikimedia Commons

Chrysanthemum Stunt Viroid (CSVd)

Common Symptoms: stunting, spotted leaves, poor rooting, flower color change, disruption of photoperiod response for flower initiation. It is one of the biggest threats to the chrysanthemum production industry.

Effects of CSVd on florist chrysanthemum. Source:

Oafish Oomycetes

While many still lump oomycetes in with fungi, many scientists consider them to be a distinct group because they have a number of differences. One common name for this group is “water mold” because of their preference for wet environments and their mold-like appearance. While they do absorb nutrients and produce mycelia like fungi, there are differences in their composition, genetics, and reproduction. The biggest difference is the production of oospores, which are thick-walled reproductive spores that can rest, or hibernate, for extended periods of time in unfavorable conditions and “germinate” when conditions are favorable for the organism to grow and reproduce. Another difference is the composition of its cell walls. Fungi cell walls are composed of chitin, which is the same chemical that gives hardness to the exoskeleton of insects. Oomycete cell walls are composed of cellulose and beta glucans (polysaccharides that make soluble fibers).

While late blight of potatoes Phytophthora infestans is often called a fungus (and I discussed it in the fungus installment), it is technically an oomycete. The same with downy mildews of various species (Plasmopara) and blights caused by Pythium spp.. One of the more devastating oomycete diseases is Sudden Oak Death Phytophthora ramorum, which as it sounds, is responsible for the sudden death of plants. But many are now calling it Ramorum blight because it effects way more plants than just oak (Rhododendron, Viburnum, Camellia, Azalea, blueberries, Douglas fir, lilacs, and mountain laurel to name a few). Early symptoms of Sudden Oak Death include foliage dieback, leaf discoloration and water-soaked lesions, shoot and twig dieback. As the disease progresses, trees develop cankers that ooze or bleed dark colored sap and eventually decline and die. There is no treatment or cure for sudden oak death and prevention relies on good sanitation and abiding by quarantine regulations.

Oozing oak canker from Ramorum Blight/Sudden Oak Death. Source: Ohio State University Extension
Water soaked lesion on Rhododendron caused by Ramorum Blight. Source: UMD Extension

Wrapping it up

Just like diseases caused by the familiar fungi, bacteria, and viruses, these plant diseases can be devastating and difficult to prevent or manage. As always, an ounce of prevention is worth a pound of cure (which is really true when there isn’t a cure). The best way to deal with these diseases, as with any disease, it to practice integrated pest management with good sanitation, procuring plants from trusted sources, and being vigilant for signs of disease so that infected plants can be removed quickly to reduce the chance of spread.

Knowing some of the common diseases and their signs and symptoms is key in early detection and decision making. Hopefully, some of the info I’ve shared in this series can help you keep an eye out for diseases. As always, when in doubt contact your local extension office for help with diagnosis, verification, and to discuss possible treatment or prevention options.


Underrated Beneficial Arthropods Part 1: Pollinators

The world of beneficial arthropods (insects and their relatives) far exceeds some of the common critters that we often associate with this category. Many of them perform vital functions in our own yards, gardens, and ecosystems all over the world. A very small sliver of all arthropods are considered pests of any kind though there are certainly some pretty devastating pests in this category. Most of these other organisms are either providing benefits or maintaining important ecosystem functions. They are often overlooked, as some of the more charismatic ones (like butterflies, bees, mantids, and lady beetles) take most of the spotlight. These other not-so-glamorous beneficial arthropods are just as important as the more famous ones, and often perform many tasks that go unseen and underappreciated.

I wanted to talk about each group of common beneficial arthropods (Pollinators, Natural Enemies, and Nutrient Cyclers), but as I was writing, I admittedly got a bit carried away. So in order to prevent this blog post from being extremely long, I decided to split this into 3 parts. Stay tuned for the next installments in my spring and summer GP blog posts. In the meantime let’s dig into some under-appreciated pollinators.

Underrated Pollinators

Goldenrod Soldier Beetle ( Chauliognathus pensylvanicus) feeding on pollen. Photo: Abiya Saeed

Ah yes, pollinators! Many people consider this their favorite category of beneficials (because very few things are as striking or charismatic as a bee or butterfly sipping nectar from a flower). This is also one of the first groups that come to mind when people think about beneficials in general. The classic image of a monarch butterfly or a honey bee on a flower is often associated as the representative image of this group. That being said, honey bees are just one example of the over 20,000 bee species that are found worldwide. But this group far exceeds butterflies and bees- and some of the less charismatic critters often get an unfair reputation, or just a lack of awareness about what they do. For a variety of reasons, including their anatomy, efficiency, abundance, and direct economic impact, bees are considered the most important pollinators. But many other animals are also great pollinators, some of which are the sole pollinators of certain plant species. In fact most arthropods that visit flowers have the potential to move pollen around, making them possible pollinators. But since I don’t have time to write a whole book’s worth of information into this blog post, I will focus on a few of the larger groups of these less famous pollinators. If you are interested in doing a deeper dive into the world of beneficial arthropods, I will include some resources at the end.


Flies (order: Diptera) are a huge group of insects, with over 110,000 described species in 150 different families. This group spans a wide variety of very well-known groups like house flies [Muscoidea] and mosquitoes [Culicidae], to not so well-known groups like stalk-eyed flies [Diopsidae] and long-legged flies [Dolichopodidae]. They encompass nearly all biomes and have a broad range of functional groups including predators, parasites, decomposers, and pollinators. In fact, some studies consider flies to be the second most important flower visitors after bees.

Green Bottle Fly (Lucilia sp.) on a Prickly Pear (Opuntia sp.) Photo: Abiya Saeed

According to a literature review by Cook et al. (2020): flies from 86 different families have been reported to visit over 1100 plant species. These flower-visiting fly species also include some that have important potential for crop pollination and have been recorded to visit many horticultural crops. This includes commonly known pollinating flies, e.g., bee flies [Bombyliidae], hoverflies [Syrphidae], and flower flies [Anthomyiidae]. But some flies we don’t usually associate with this role such as blow flies [Calliphoridae], flesh flies [Sarcophagidae], and horse flies [Tabanidae], and some that many may never have heard of such as nose flies [Rhiniidae] and march flies [Bibionidae], are included. Some species are even considered to have potential as managed pollinators, a role that we most commonly associate with honey bees and some other bee species.

Fun fact: only female mosquitoes need a blood meal in order to reproduce, whereas male mosquitoes feed on nectar, making mosquitoes pollinators! In fact, mosquitoes have been studied as pollinators of orchids, like the Blunt-leaf Orchid, Platanthera obtusata, among other plants.


We all know butterflies and moths (order: Lepidoptera) are well-documented flower visitors and important pollinators. Despite this, butterflies often get most of the limelight and attention from the general public while many moths often end up being overlooked. Even though moths make up nearly 90% of the over 160,000 described Lepidoptera species, there is a disproportionate amount of research that has historically been conducted on them when compared with butterflies. It has also been demonstrated that moths are the most important nocturnal pollinators, which is fairly intuitive when you think about their nocturnal foraging biology. A study conducted in Sussex by Anderson et al. (2023) demonstrated that moths had higher pollen deposition rates on bramble species indicating that they are more efficient pollinators of brambles than their diurnal counterparts. This has implications for the importance of moths in other plant groups as well, as new research continues to be conducted.

Clearwing Moth (Hemaris sp.) Photo: Steven Katovich,

Fun fact: My favorite story to tell about plant-pollinator interactions is of Darwin’s Star Orchid (Angraecum sesquipedale). Charles Darwin was sent a sample of this striking orchid from Madagascar in 1862. Upon examination he found that the nectar tubes were 30 cm (~12 inches) deep! Based on this, Darwin hypothesized that it would take something that has a really long tongue to be able to access that nectar but nobody believed there could be such an insect and he was ridiculed by other scientists. In 1867 Alfred Russel Wallace examined the orchid and predicted there must be a moth in Madagascar that can reach this nectar in order to pollinate the plant. But no moth had ever been discovered which had a proboscis (a coiled and elongated mouthpart of butterflies and moths that is used to suck up nectar) that long. It wasn’t until decades later in 1903 a moth meeting these specifications was discovered. Aptly named in honor of the scientist who predicted its existence, Wallace’s sphinx moth (Xanthopan praedicta) also known as the ‘predicted moth’ has the longest proboscis (sometimes referred to as a tongue, though it is not quite a tongue) of any insect. This just demonstrates just how amazing plant and insect interactions and coevolutionary relationships truly are!

The Star Orchid alongside the ‘Predicted Moth’! Photographed by Robert Clark for Evolution


Wasps are in the order Hymenoptera, shared with bees and ants. They often have a bad reputation due to a few particularly aggressive social wasp species that most of us have likely had an unfortunate interaction with. That being said, the wasp group is extremely large, diverse, and species-rich. With over 103,000 described species in the category (and scientist estimates stating that the actual number could be in the millions), wasps span a lot of crucial categories of beneficials including parasitoids, predators, and pollinators.

Many wasp species resemble bees and it can be easy to confuse them for each other when they are visiting flowers. The major differences between the two are the thread-like waist that wasps have, and their less-hairy sometimes shiny, overall appearance. In addition most wasp species are primarily carnivorous, feeding on insects and other sources of meat for their protein needs, making them a great resource for deterring common garden pests (stay tuned for more on that in the next part of the Underrated Beneficials series). Even though most of these wasps are carnivorous, they supplement their diet with sugars which they often get from nectar or honeydew produced by sap-sucking insects, e.g., aphids, and occasionally fruit.

White-Striped Black Mason Wasps ( Pseudodynerus quadisectus ) mating on a Goldenrod (Solidago sp.) Photo: Abiya Saeed

There are also some species of vegetarian wasps. A common example of these are the 300 species of pollen wasps (Masarinae) which, like bees, are nectar and pollen feeders (and many of which are important pollinators of certain plant species, such as the Water Leaf, Hydrophyllaceae).  Due to the fact that they have fewer hairs, wasps aren’t as efficient at pollination as bees, however, they can still be very important pollinators. Like bees, some wasps are generalist pollinators, visiting a wide-array of flowering plants, while others are specialists where a group of wasps relies on a group of flowering plants and vice versa. In these cases the pollination of those plants are reliant on these wasps.

Studies have shown that some generalist wasp species are better than some generalist bees at pollinating specific flowers. A 2018 study by Thomson examining the pollinators of the California Bee Plant (Scrophularia californica) showed that the western yellowjacket (Vespula pensylvanica) was a more effective pollinator in terms of pollen deposition when compared with honey bees and bumble bees. Some species of African pineapple lilies (Eucomis autumnalis and Eucomis comosa) and African milkweed (Pachycarpus grandifloras) are primarily pollinated by spider-hunting wasps (Pompilidae) in the genus Hemipepsis. Additionally over 100 species of orchids are reliant on wasps for pollination some of which use sexual mimicry to attract male wasps to flowers! And I would be remiss if I didn’t mention fig wasps (family: Agaonidae), who have been coevolving with their host plant for tens of millions of years. The fig (Ficus sp.) ‘fruit’ is actually an inflorescence (an enlarged stem with lots of little flowers inside). In order to pollinate those flowers, the female fig wasp squeezes into a small opening and moves around, laying her eggs in the ovaries of these flowers thereby spreading pollen from the fig that she was born in. The male offspring will remain in the fig while the new batch of females will emerge and look for a new fig in which to lay their eggs (see resources for more on this fascinating mutualism).

For more information on wasps as pollinators, check out the awesome article by Hooks and Espíndola, linked in the resources!

Fun fact: Sexual mimicry is used by some flowers to attract their pollinators. In these situations, the flowers use a combination of visual and chemical cues including mimicking the scent of specific female wasps and bees to attract males. An example of this can be seen in the wasp family Thynnidae, where male winged-wasps are searching for wingless females to mate with. When they stumble across the warty hammer orchid (Drakaea livida) they confuse it with a female thynnid wasp, because of the similar shape and scent, and try to mate with it. This process results in the pollen being deposited on the abdomen of the male wasp. As he goes to the next orchid in order to mate, the pollen is deposited on the new flower, resulting in pollination.


Beetles (order: Coleoptera) are considered to be the largest insect order with over 350,000 described species, which makes up 25% of all known animal species on Earth! Like some of the previously mentioned orders, they include a large diversity of functional groups, including pollinators. Due to the incredible size of this order, they are considered to be the largest and most diverse group of pollinators with an estimated 77,000 flower-visiting species. In fact, based on pollen-covered specimens preserved in amber from 100 million years ago which is 30 million years earlier than the first records of bee pollinators, beetles are considered to be the first recorded insect pollinators! Even now they are considered to be vital pollinators of some of the most primitive flowering plant groups that still exist today, such as Magnolias.

Flower Longhorn Beetle (Analeptura lineola) on a Multiflora Rose (Rosa multiflora). Photo: Ansel Oommen,

Although some beetles are specialists of certain plant groups ,especially those that are descendants of some of the earliest flowering plant groups including water lilies and magnolias, most are generalist pollinators and will visit a wide array of flowering plants. Some scientists even estimate that flower-visiting beetle species will visit 90% of all 350,000 flowering plant species. Beetle pollination is also essential for certain agricultural crops including Paw Paw (Asimina sp.) and the Atemoya (Annona x Atemoya).

For more information on the fascinating world of beetle pollination, check out the awesome article by Hooks and Espíndola, linked in the resources!

Fun fact: The process of cross-pollination that depends on beetles is referred to as ‘cantharophily’.


Cook et al. (2020). The Role of Flies as Pollinators of Horticultural Crops: An Australian Case Study with Worldwide Relevance.

Anderson et al. (2023). Marvellous moths! Pollen deposition rate of bramble (Rubus futicosus L. agg.) is greater at night than day.

Hooks and Espíndola. (2017). Wasps, surprisingly cool pollinators.

The story of the fig and its wasp.

Hooks and Espíndola. (2017). Beetles and Pollination.