Month: January 2024

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.

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.

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.

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.

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.

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.

If you are interested in reading more about how wind affects gardens, check out my earlier blog post at https://gardenprofessors.com/who-has-seen-the-wind/.

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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.

First, let’s consider the Credibility of the source. According to HouseDigest.com, 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.

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.”

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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.

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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.

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.”

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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?

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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.

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:

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:

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).

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.

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.

So, I moved on and created “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.

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.

Deciduosity

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.

Solutes

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.

Seeds

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.

Roots

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.

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:

• https://gardenprofessors.com/noraking/
  
• https://gardenprofessors.com/leaves-for-lawn-fertilizer/
  
• https://gardenprofessors.com/one-trees-leaves-over-400-kinds-of-bacteria/

References

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
https://pubmed.ncbi.nlm.nih.gov/28215078/

Fadon, E. E. Fernandez, H. Behn, and E. Luedeling. 2020. A conceptual Framework for Winter Dormancy in Deciduous trees. Agronomy 10(2), 241; https://doi.org/10.3390/agronomy10020241

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.
https://www.jstor.org/stable/48719251

Stavi, I. 2020. On-Site Use of Plant Litter and Yard Waste as Mulch in Gardening and Landscaping Systems. Sustainability 12(18), 7521; https://doi.org/10.3390/su12187521