The nitty gritty on movement of chemicals in plants, part 2

My social media administrator (aka cat herder extraordinaire) reminded me recently that I’d written a post on xylem function and promised to follow up the next month with a post on how phloem works. Well, that was about 18 months ago. Guess I better keep my promise.

Do read the linked post if you don’t remember why “xylem sucks.” In contrast to xylem, functional phloem is an interconnected series of living cells with cell membranes. The presence of a membrane means the plant can regulate what goes in and out of the phloem, and the direction of phloem flow is determined by the relative concentrations of dissolved substances in the water – most importantly sugars derived from photosynthesis. Areas of high sugar concentration are sources; areas of low sugar concentration are called sinks. As these words suggest, phloem contents are moved from the source to the sink. This process is called translocation.

A general schematic depicting both xylem and phloem movement. Courtesy of Wikipedia.

The most obvious sources in plants are leaves and other green tissues: this is where photosynthesis takes place and sugars are created. Other less obvious sources are woody roots, trunks, and branches: carbohydrate reserves are built up in the fall, as winter-hardy species enter dormancy and deciduous plants shed their leaves. Carbohydrates are re-mobilized in the spring when trees, shrubs, and perennials emerge from dormancy.

The carbohydrates stored in the branches, trunk, and roots of trees will provide energy to leaves as they emerge in the spring.

Like source tissues, sink tissues vary with the season but can also change daily – especially during the growing season. Expanding leaf and flower buds demand energy for building new cells; ripening fruits require large quantities of sugars. As new branches grow and produce leaves, their demand for carbohydrates decreases until they become source tissues. Translocation is a complex, dynamic process, where phloem in different parts of the plant translocate sugars in different directions.

Newly developing leaves without chlorophyll are sinks for translocated carbohydrates.

This information can be used to guide your gardening practices:

Application of translocated herbicides. While we always want to reserve chemical weed control as a last resort, sometimes it’s necessary when other methods aren’t successful. Glyphosate (the active ingredient in Roundup) is applied to leaves and is carried through the phloem to sink tissues. When you read the label on a glyphosate-containing herbicide, it will mention that late summer/fall application is needed to kill the roots of perennial weeds. Consider hedge bindweed (Calystegia sepium), a pernicious and difficult weed to remove by mechanical or cultural means once it’s established in a garden or landscape. Glyphosate will successfully kill this weed but only if it’s applied after flowering. At that point the plant is no longer putting resources into either flower production or vegetative growth; instead, translocation moves carbohydrates (and the glyphosate) to the roots for storage over the winter. Killing the underground storage tissues means this herbaceous perennial will not reappear the next spring.

Bindweed can be almost impossible to remove.

Pruning the crown during the growing season. When plants are actively producing new leaves and flowers, translocation is generally directed towards these tissues. Pruning leaf-bearing branches and stems has two consequences: removal of source tissues (the leaves) and increased demand for resources from the rest of the plant. Carbohydrates are moved from other sources, like remaining leaves and woody storage tissues, to the expanding stem and leaf buds that have been stimulated by pruning. This is why chronic and/or severe pruning can have a dwarfing effect on woody plants: woody storage tissues are depleted of their resources which are translocated to the developing buds. Until the new growth leafs out, it will remain a sink tissue.

Newly emerging larch needles will become source tissues once they finish expansion.

Pruning the crown after transplanting. Take the information from the previous section and now consider the additional sink that has been created during transplanting. Successful establishment of a newly installed plant requires rapid development of new root tissues. Pruning the crown of new transplants siphons much of the stored resources away from the roots, reducing the rate of root growth and establishment. Reduced root establishment also means reduced uptake of water, which will damage the newly expanding buds and leaves. Bottom line: do NOT crown prune after transplanting, except to remove diseased, damaged, or dead branches. Wait until the following year to undertake any structural pruning.

Fine roots must establish quickly to provide water for the entire plant.

Tropical storms and hurricanes and how they affect your gardens and properties

Last month I discussed the forecast for the Atlantic tropical season and pointed out that it is likely to be an active one. As I write this, there has already been one named storm (Alberto, which went into Mexico but dropped a lot of rain in southern Texas) and two more areas of potential development are moving their way through the Atlantic (note TS Beryl formed on Friday, June 28 at 11 pm after this was written). Hurricane season has begun! This month I will discuss what a tropical storm is and how they form into hurricanes. I will end by discussing how tropical storms and hurricanes impact gardens and what you can do to prepare for them.

Epilobium canum “Hurricane Point” in Clovis Botanical Garden, Krzysztof Ziarnek, Kenraiz

Where do tropical storms and hurricanes form?

While we think of hurricanes as hitting the southeastern part of the United States, they are actually much more widespread than that. The map below shows that tropical storms can form in both hemispheres and affect every continent except for Antarctica. Here in the United States we see them most often over the Atlantic Ocean but can experience storms on the west coast from time to time as well. The storms are not always called hurricanes, they can be called typhoons in the Western Pacific and cyclones in the Indian Ocean and Australia. To be considered a hurricane or one of these other storms they have to record a sustained wind speed of 74 mph or higher. Storms in the United States that are stronger than that are classified by the Saffir-Simpson scale into categories 1 through 5 depending on how strong the winds are. And of course the wind gusts in the storms can be quite a bit higher than the sustained winds, they are just more localized and last for only short periods.

Global hurricane track climatology. Source: NASA Space Observatory.

What ingredients are needed for a tropical storm or hurricane to form?

The prerequisite conditions for hurricanes are: warm, deep ocean waters (greater than 80°F / 27°C), an atmosphere cooling rapidly with altitude, moist middle layers of the atmosphere, low wind shear, and a pre-existing near surface region of low pressure in the surface environment. But you might have noticed from the map that even if these conditions are in place a tropical cyclone is not likely to form if it is not at least 300 or so miles from the equator. This is because of the Coriolis force which acts on moving air on a rotating planet to push air to the right of the original direction of movement in the Northern Hemisphere and to the left in the Southern Hemisphere. Low pressure draws air into the circulation, but the Coriolis force helps it to spin up into a storm with a defined circulation.

The seeds of low pressure where storms form can come from atmospheric waves moving east to west off of Africa, sometimes from stalled fronts over the Gulf of Mexico or along the East Coast of the United States. These usually provide the initial trigger of storm development. But not all waves or fronts can develop into cyclones if the other conditions are not right. The location of typical development depends on the time of year, with early and late storms developing closer to the United States and most storms in the peak period from mid-August to mid-October forming from waves coming off the west coast of Africa.

You might wonder why there are almost no tropical storms in the southeastern Pacific or in the southern Atlantic Ocean. That is because the water is normally too cold to sustain storm development. Since ocean temperatures are warming over time we could see more storms there in the future, especially in the South Atlantic where temperatures are already warmer than the SE Pacific. The tropical season could also become longer as the ocean warms up to 80 F earlier in the year in the future.

Bermuda high and tropical storm tracks. Source: Accuweather.

Tropical storms and hurricanes move under the influence of winds midway up in the atmosphere which push along the core of the storm as it is growing or weakening. The stronger the core of the storm, the closer the link between the large-scale atmospheric pattern and the storm movement. In the map above you can see that most storms move in a curving pattern that begins in the east near the equator and moves west over time before recurving to the northeast in a clockwise manner. This pattern is caused by subtropical high pressure, called the “Bermuda High”, over the Atlantic but by other names in other parts of the world. The path of each storm is unique due to the weather pattern present at the time of the storm, and sometimes they can take some crazy paths if the weather pattern is unusual.

How do tropical storms become hurricanes?

Usually, a wave of low pressure over the ocean pulls in air towards the center to reduce the pressure gradient. As the air moves in, the Coriolis force causes it to start spinning. In the Northern Hemisphere this spin is counterclockwise. The air above the surface circulation starts to flow out of the storm and drops the pressure at the surface causing the storm to intensify as air rises near the center of the storm. This continues as long as there is a source of energy (warm water) below it and there is no jet stream high up in the atmosphere to disrupt the development of the circulation. When the sustained wind speed reaches 74 mph its designation is changed from Tropical Storm to Hurricane and it stays that way until the wind speed drops as the storm weakens over land or colder water.

What impacts do tropical cyclones have on gardens and what can you do to prepare?

Tropical systems have a variety of impacts depending on where they are and how strong they are. Thoughtful gardeners will consider all the risks that severe weather can have on their gardens and get ready long before the storms hit. The strong and gusty winds are the most apparent impact; they can cause damage to trees, buildings, and plants and can cause significant damage to gardens. It’s a good idea to walk through your property periodically to look for dead or diseased limbs that could become airborne missiles in strong winds (whether or not they are from a hurricane). Decorative items and furniture left outside can damage tree trunks as well as houses and gardens when they become wind-borne. So if a storm is imminent, scout your property to remove anything that could be potentially hazardous.

Another important impact is flooding rain. The amount of rain that falls from a hurricane depends in part on how fast it is moving, since a slow-moving storm can drop more rain on a particular spot than one that is moving through quickly. The storm does not have to be strong to produce a lot of rain either—some of the weaker storms have been great rain-makers. And it does not even need to be an organized storm. Wet tropical systems that are not fully organized into storms have the potential to produce flooding rain, as we saw in southern Florida just a couple of weeks ago with over 20 inches of rain in some locations. The remains of hurricanes can also cause floods far inland, especially if there are mountains to help the air rise. Hurricane Agnes in 1972 had damage from the Caribbean all the way to Canada because of the torrential rains that fell along the Appalachian Mountains as it moved north. Gardeners who live in areas where flooding is likely should plan ahead to divert rain into rain gardens away from their planting beds to reduce erosion and keep soil from becoming saturated.

Hurricane Ivan, 2004. Source: NOAA.

Hurricanes can also cause other impacts too, especially if you are near the coast. Storm surge can drive sea levels up to 25 feet above mean sea level as the water builds a dome under the area of lowest pressure that moves along with the storm until it makes landfall. If you are in a coastal area, you need to consider what the elevations of your land and house are so you know how much the water might rise in a strong storm. Another impact is the strong storms that can occur in the spiral bands outside the main circulation. These storms can hold weak tornadoes as well as heavy rain and gusty winds. In Hurricane Ivan in 2004, we had a tornado in Athens GA at the same time that the main storm was making landfall along the coast several hundred miles away.

As gardeners, it is important to keep in mind that tropical storms and hurricanes are not all bad. The rain that comes from these storms may include 30-40 percent of the summer rain that is expected to fall in a tropical area, and if few storms come, drought is more likely.  But the damage is also like to stress your gardens (not to mention the gardeners!), so learning more about these storms and planning ahead to prepare for the damage they might bring is a good thing for every home owner in an area prone to tropical activity to do now, before the storms come.

Trees on the levee along the Mississippi River bend over as the high winds from Hurricane Gustav pass over the Carville-St. Gabriel area in south central Louisiana. Source: US Army, https://www.dvidshub.net/image/112209.

The truth is out there – you just need to know where to look. Part 1 – navigating the informational swamp

Good and good for you!

It’s been 20 years since I began my Extension position at Washington State University. During that time, I’ve tackled gardening myths and produced peer-reviewed fact sheets and manuals through our Extension Publications department. But because of the way that Google searches work, these resources are often buried far beneath the glitzy but fact-free websites promoting bad science. This month I’ll be shining a spotlight on some publications that are must-reads for those who wish to use science-based information in their garden and landscape activities.

If the sheer vastness of the online swamp of information horrifies you, there’s no better place to start than with our Scientific Literacy manual. This publication, coauthored with Dr. Catherine Daniels, introduces you to the CRAP (Credibility, Relevance, Accuracy, Purpose) analysis of information from any source. As the abstract states, this publication helps you “to distinguish science from pseudoscience and can help avoid wasting time, money, and resources on poor ideas or, worse, scams.”

With the CRAP analysis techniques under your belt, you will appreciate our fact sheets debunking some of the “plausible nonsense” force-fed to gardeners (and by extension their plants and soils). The use of Epsom salt in the garden is one of the biggest fact-free nostrums out there. Our Epsom Salt fact sheet, coauthored by Rich Guggenheim, outlines what misapplication of Epsom salt will do to your garden soils and the news is not good.

Right up there with Epsom salt is gypsum, another popular soil amendment with many purported benefits. While gypsum can alleviate problems in heavily used agricultural soils, it has little to no benefit when applied to gardens and landscapes. Our Gypsum fact sheet, also coauthored by Rich Guggenheim, will tell all!

Proper soil nutrient management depends on your gardening goal.

Since we’re discussing chemicals that are added to soils, I’ll refer you to another article written by Dr. Jim Downer and myself. Soil myth-busting for Extension educators – reviewing the literature on soil nutrition is a peer-reviewed publication in the Journal of NACAA. In this article we discuss address “six common misperceptions about managing soil nutrition in nonagricultural situations.” And yes, two of these misperceptions are the routine use of gypsum and Epsom salt.

Scooby Doo and the gang tackled the Swamp Monster – you can too!

I invite you to use the methods in our scientific literacy manual to debunk claims you read or hear about soil amendments. Knowledge is power and you can become a gardening superhero by helping fight the gardening swill that fills the informational swamp.

Next month I’ll continue the “truth series” with a look at some of our publications on garden practices we believe to be true…but aren’t based on science. In the meantime, here a couple of related blog posts that you might enjoy:

I do my version of the shame list with the “Dirty Dozen Garden Products.” Not only is this a good reviews of things that don’t belong on your garden soils, but there’s a fun quiz to see how your stack up with science.

This post on “Garden Logic” links up nicely with our discussion of CRAP analysis. Find out why we tend to jump to conclusions about what we see in the garden, regardless on whether it’s evidence-based or not.

Stay tuned for next month!

Don’t be a Horticultural Hot Mess: Climate-Smart Gardening Practices

While there are still doubters out there mostly thanks to politics, it is pretty clear that the climate is changing and humans are affecting the speed at which it is occurring. The number of record-breaking temperatures and the shift in the USDA hardiness zones show the current effects of this change that will affect almost all parts of our lives, including gardening. What may be less apparent to folks is shifting weather patterns and the increased incidences of extreme weather. Just ask farmers about the weather and they can tell you how extreme weather has gotten. The funny thing is that while many farmers may doubt the existence of anthropogenic (human-caused) climate change, research has show that they believe that weather has gotten worse and that they change their practices and livelihoods to cope with those changes. So as gardeners we can also adjust our practices to deal with the changes as well.

I live in Omaha, Nebraska and we definitely have seen this uptick in extreme weather events this year. From over a dozen tornado touchdowns during the afternoon of Arbor Day (some friends and I got to shelter in place at a warehouse box store for a few hours that day) in a system that had 145 tornadoes across the Midwest. May 2023 was the driest month on record with just 0.17” of rain, feeding the already severe drought in the area. On the other hand, May 2024 was the second wettest May and the eight wettest May on record with 11.14” of rain – the amount that we would normally expect to receive between January 1 and June1 in any given year.

Tornado outbreak of April 26–28, 2024 - Wikipedia
There were 145 tornadoes tracked between April 26 & 28, 2024.

As gardeners we should consider both the long-term implications climate change and the short-term weather extremes that it brings and what sort of mitigation strategies may be needed. And while the individual effect of practices to reduce or sequester greenhouse gas emissions might be minimal, if many people practice climate-smart gardening there could be a small impact – every little bit helps.

Mitigating practices for climate-smart gardening

At this point the change is already happening, so it is wise to think about what practices we need to adopt in the garden to deal with current weather pattern changes and the overall changes of the climate such as increased heat and changing precipitation (some places get less, some places get more). Here are some things to think about:

Plant climate-resilient plants

The advice I often see is that gardeners should “just plant natives,” but it isn’t really as simple as that. Yes, native plants are adapted to the current environment of the area, but will they necessarily be adaptable when that environment changes? The native range for many plants, namely cold intolerant ones, will expand as more areas warm. But some plants can’t take the heat. Changing weather patterns also means that areas may become drier or wetter which could affect what grows successfully in an area. To add to this double whammy, most gardeners are planting in urban areas that have been drastically altered from the local native habitat in terms of soil, temperature, water, and more which may make conditions less favorable for native plants. It isn’t guaranteed that what grows as native today will survive in tomorrow’s climate.

It is best to take a blended approach – incorporating native plants that are likely to do well in evolving climate conditions and adding introduced plants from areas similar to what the climate is changing toward. Also keep in mind that many plants, especially fruit trees, require a certain amount of cold weather, referred to as chill hours. These requirements make it difficult, if not impossible, to grow many cultivars of fruits like apples, pears, plums, and blueberries in southern Florida, Texas, and California. As temperatures rise, the areas that struggle to grow these fruits will expand. It is even difficult to grow crops like tomatoes in some of these areas because extreme heat sterilizes pollen and slows fruit maturation. Resilient gardeners may have to turn to climate resilient (heat tolerant) vegetable cultivars in the future.

Chilling Hours: between 35°F and 45°F, Oct. 1 start
Source: Midwestern Regional Climate Center

different fruit and nut tree species ...

Source: Climate change trends and impacts on California agriculture: a detailed review

Improve Soil Health

Healthy, organic-matter rich soil retains water better and supports plant nutrition. Supporting plant health makes them better able to grow when environmental conditions aren’t exactly perfect. Soil organic matter collects and holds water over long periods, making it available to plants longer term if conditions become dry. It can also aid in drainage if conditions become wetter. Increase organic matter through the application of mulches and composts. In vegetable gardens, cover crops can also be an effective means of adding organic matter and nutrients to the soil.

Water Management

Aside from building soil health to retain water, using mulch to reduce evaporation can also effectively improve water management. Organic mulches also help reduce and moderate soil temperatures, which is important especially during extreme heat periods.

Using effective and efficient irrigation can also help keep plants healthy while reducing water usage. Many perennial plants adapted to current environmental conditions (whether they are native or not) can survive without large amounts of water input during normal periods of precipitation. However, during extreme heat or drought even low-water plants may need supplemental water. Most all plants also need supplemental water for the first few weeks or months after planting until they are established.

Create Microclimates

It is a fairly common practice to create microclimates to protect tender plants in cold weather, such as planting near walls or using protective structures like low tunnels or high tunnels for vegetables and fruits. As temperatures rise gardeners may need to consider creating microclimates to protect plants from heat or extreme conditions like wind. The use of shade cloth or shady areas, trellises, and wind breaks can help protect from extreme temperatures, harsh winds, or excessive sun exposure.

File:烏來生態農場溫室草莓.jpg - Wikimedia Commons
Shade structures to reduce heat. Source: Wikimedia Commons

Planting Adaptations

Aside from changing what is planted, when things are planted might also need to change. Planting times for vegetables, fruits, and annuals will likely shift earlier, especially in areas with extreme heat that would negatively effect plants.

Promote Biodiversity

Planting a variety of plants, both native and introduced, will be helpful if the environment becomes unsuitable for certain species. That way, you haven’t put all of your eggs in one basket. Biodiversity will also support wildlife and insect populations that will also be effected by the changing climate. Having a variety of plants for food and shelter will be paramount for supporting pollinators, songbirds, and other species.

Can you effect climate change from your garden?

Like I said earlier, individual garden practices would likely have little effect on slowing climate change, but if lots of gardeners change practices there could be an effect, even if it is somewhat minimal. Every little bit helps. I left extension back in October to work for a company that supports farmers in conservation and climate-smart practices that add carbon to the soil and therefore reduce greenhouse gas emissions. The effect of an individual farmer would be minimal, but working with hundreds or thousands of farmers and hundreds of thousands of acres of crops can have at least some impact.

So what can you do as a gardener? The thing that most people think about is reduced usage of power equipment that relies on gas or diesel. While electric and battery tools rely on the electric grid that still uses fossil fuels, as the grid continues to add renewable and sustainable energy sources the carbon footprint will continue to shrink.

But one of the best things gardeners can do goes back to soil health. Organic matter build up in the soil sequesters carbon. Therefore practices that add organic matter to the soil can also have an impact on greenhouse gas in the atmosphere. Adding organic matter is a starting point, but you want to make sure it stays there. In annual production systems like in vegetable gardens, tillage promotes the decomposition of organic matter which releases the carbon back into the atmosphere. Minimizing soil disturbance by adopting no-till practices is a key step gardeners can take to reduce their carbon footprint (and positively effect soil health). Eliminating soil disturbance when establishing new perennial beds is also beneficial, but perennial plantings, especially trees, are great at sequestering carbon deep in to the soil for the long-term.

Sources

“Hot, hot, hot!” –A new source of heat information for gardeners and a look ahead to the 2024 Atlantic tropical season

We are entering the hottest time of the year for most of our readers except for those who live in the Southern Hemisphere or in tropical locations where there is not a big seasonal cycle. Heat can have a big impact on both gardens and gardeners, so this is a great time to look at a new product that is now available from the National Weather Service to alert people who spend time outside to the dangers of high temperatures. This new HeatRisk product will help you use the 7-day forecast to identify times when the heat will be the most severe—which will allow you to plan your outdoor work accordingly to avoid the worst dates and times of dangerous heat conditions. I will also provide some resources for how heat affects plants from The Garden Professors and briefly talk about one potential consequence of high temperatures on the upcoming Atlantic tropical season, which starts June 1 in the United States.

Sunset at Cholla Cactus Garden, Joshua Tree National Park, NPS/Brad Sutton, Commons Wikimedia

How does high heat affect gardeners?

Usually when we talk about heat, we are talking about high temperatures. But as they say, “it’s not (just) the heat, it’s the humidity.” High temperatures alone can cause problems for humans and animals because our bodies are built to work best in a narrow range of temperatures. If the temperature goes above that range (or below it), our physical systems experience distress and eventually will shut down. High humidity makes it worse because it makes our natural ability to cool off by sweating less effective because the water on the skin from sweat does not evaporate readily when the water content of the air is high. Many indices for the heat index factor in both temperature and humidity, and the wet bulb globe temperature (WBGT–more on this in a minute) includes temperature, humidity, wind speed, and solar radiation because all of these factors can affect the body’s ability to cool off.

Grassland in a heatwave, Stefan Czapski, Commons Wikimedia.

If you are outdoors for a long time and start to experience dizziness or nausea or even worse become unconscious, then you are likely experiencing a heat-related illness and you need to get to a cooler area where you can recover right away. In the worst cases, a trip to the hospital may be needed when the body temperature is elevated above the safe range for human life. You can learn more about protecting yourself from high heat at Heat.gov.

What is the NWS HeatRisk map?

Fortunately, there are number of online tools available that can help identify days and times when the danger from high heat is most likely. The National Weather Service has just released a new experimental product called HeatRisk, which provides an interactive map that shows where the heat will be the most dangerous over the next few days. An example of the map is shown below. You can either zoom in on the map or click on your location to get a specific temperature forecast for that spot.

Another tool that may be useful is available across the United States from the Southeast Regional Climate Center at https://convergence.unc.edu/tools/wbgt/. Their tool produces hourly forecasts of WBGT based on National Weather Service forecasts for several days ahead at whatever US location you choose (not just the Southeast) that can determine when conditions are most dangerous for working or playing outside. The WBGT is often used by sports teams to determine if it is safe for players to practice outdoors and how often they need to take a break. The tool gives you the choice of several state regulations for threshold values for WBGT that should determine whether football or other practice is safe. The same information can be used to decide if outdoor workers need extra water breaks in the shade or when gardeners should come in, cool down, and rehydrate.

How does high heat affect plants and gardens?

Plants respond differently to heat than humans and other animals do because they don’t sweat. High heat can cause the plants to close the stomas in their leaves to retain moisture but a long enough period of high temperatures and dry conditions with little soil moisture leads to wilting and eventually, death of the plants. I am not an expert on this, but fortunately Jim Downer and other GP authors have written several blog posts in the past that address the effects of heat stress on plants. John Porter has also written on the effects of high temperatures on pollination and ripening. Check out some of these posts, especially Jim’s post on abiotic disorders, to see what effects high temperatures may have on your garden.

What do we expect from this year’s Atlantic tropical season and how is it related to high temperatures?

This year we have seen a lot of record high temperatures across the globe due in part to greenhouse warming. Sea surface temperatures in the northern Atlantic Ocean have been especially high, most likely due to a combination of greenhouse warming and the absence of aerosol particles in the atmosphere due to the switch to cleaner fuel for ocean vessels a couple of years ago. This change allowed more sunlight to heat up the ocean surface. These ocean temperatures are so much higher than normal that the temperatures are closer to August values than what we usually expect in late May. Since hurricanes feed and grow over water than is warmer than 80 F, it means that the atmosphere over the main development region for Atlantic tropical storms is stoked and could contribute to both a larger number of storms than usual and more rapid development for any storms that do develop. It’s no wonder that the forecasts for the number of named storms in the Atlantic this year is one of the highest ever predicted. So if you are anywhere within reach of an Atlantic storm (which is most of the eastern US but also includes most of the Caribbean, Mexico, and potentially even Central or northern South America and parts of Europe), you should be prepared for tropical activity well in advance of any storms that might come your way this year.

Enjoy the hot weather but treat it with respect

If you like hot weather as much as I do, you are looking forward to the warmer weather we will see over the next few months. But if the weather gets too hot, as it is now in India, Mexico, and other places, heat-related illnesses and even deaths will become more likely. In 2023, the United States set a new record for the number of heat-related deaths. Climate change will make devastating heat waves more likely in the future, so make sure you are prepared. If you understand how heat affects your bodies, pets, and gardens and know how to take care of yourself, you will be better equipped to enjoy the dog days of summer this year and in the future as the earth’s temperature continues to rise. Be safe and enjoy the summer heat!

Sunset in Munnar Tea Garden, jisah, Commons Wikimedia.

Hort couture or hubris? The growing trend of genetically engineered novelty plants

A few months ago I wrote about the newly released Purple Tomato, one of the first direct-to-consumer genetically engineered plants made available to the general public. (I’m happy to report that my Purple Tomato seedlings are growing along quite well.) Shortly after I wrote that article, I learned about another new genetically engineered plant being released to home gardeners, this time a bioluminescent petunia. So, of course you know I just had to have some.

The Firefly Petunia was released recently from Light Bio, a company based in Idaho.  The company states that they grew out 50,000 plants for initial sale, but have worked with third-party growers to grow out additional plants from cuttings due to high demand for the plants.

The petunia itself is pretty nondescript. It is a small-flowered, white variety that wouldn’t get a second glance at a garden center. But the company introduced a set of genes from a bioluminescent mushroom called Neonothopanus nambi  that make the faster growing parts of the plants (mainly flowers, but also other growing points) glow. The glowing is caused by a reaction between enzymes and a class of chemicals called, funnily enough, luciferins. And this is bioluminescence – it glows all the time in the dark. It isn’t like a “glow in the dark” where they have to charge up with a light source and only glow for so long.

How a mushroom gets its glow
Neonothopanus nambi daytime look to night time look Source: Science News

Just like the petunia, the fungus is pretty nondescript during the daytime, but glows brightly once darkness descends. I’ve seen glowing fungus once in my life. As a kid I once saw what is called Foxfire, a glowing fungus on some decaying logs. It is pretty cool seeing something glowing so eerily in nature. Now, I have that same glow in my garden.

Back to the plants. The plants are a bit of investment, ringing in at $29 per plant plus shipping, but there are some price breaks at higher quantities if you order several or put together a group order. As a startup, I suppose the company is banking on the novelty of the plant to demand such a high price to cover costs. According to several sources, these white petunias are just the start. They’re working on roses, houseplants and more.

But why glowing petunias?

Before I placed my order, I had to take a step back and think about why. Why a glowing petunia? With the tomato there is at least the case of increased health properties with added anthocyanins. But what is a value of a glowing petunia other than a novelty? Is there a purpose? Or is it just hubris? And why are there genetically engineered plants on the market all of a sudden?

While the petunias don’t have a culinary or health value, the value that they bring is one of acceptance and familiarity. For decades now, well organized and funded campaigns have spread fear of genetic engineering. Seed companies embraced “Non-GMO” as a marketing scare tactic to drive up sales due to a fake boogie man. And even bottled water and salt are labeled as “Non-GMO”. But it seems that the tide of public opinion seems like it might be turning.

Seeing the excitement around both the Purple Tomato and this bioluminescent petunia seems to show a growing interest, or at least a waning of distrust, in genetically engineered plants. And It think that is one of the benefits, or maybe the causes, of seeing genetically engineered plants on the market. Researchers have found that the online conversation about genetically engineered organisms seems to be shifting – from less polarized to increasingly favorable.

While there are sill some hiccups and some ethical and environmental issues, most scientists see genetic engineering as the most important tool in addressing issues such as endemic plant diseases affecting staple crops and developing plants that can withstand warmer and drier conditions as the climate changes. In order for us to be able to fully use these tools, the conversation needs to continue to shift to a more favorable position.

Starting off with tomatoes, petunias, and other flowers is also a choice of ease. Growing plants that don’t have native counterparts where there could be unintentional spread of genes in the wild reduces some of the regulatory hurdles plants face in the United States. And while the purple genes introduced into tomatoes could spread to plants in the food supply, the safety risk is minimal. It would be much harder to get approval for, say, a genetically engineered sunflower or coneflower where there are wild-growing natives into which the glowing genes could inadvertently spread.

Why are genetically engineered plants popping up all of a sudden?

Probably one of the reasons we are seeing so many new genetic engineering projects now is that it is so much easier. With the discovery of CRISPR-Cas9 technology, it is much easier for scientists to transform plants with DNA insertions or extractions. This technology has revolutionized the world of genetics and genetic engineering not only in the plant world, but also in the areas of human health and more.

Before CRISPR, there were a few methods of introducing DNA into organisms. The most common one for plants was probably using a plasmid from the bacterium Agrobacterium tumefasciens. This is the cause of crown gall and it works by inserting its own ring of DNA, called a plasmid, into the DNA of the plant. The plant then produces proteins based on the virulent DNA and also replicates the DNA. One of the common method was bombardment, putting the DNA on tiny microscopic beads, usually gold, and shooting them into the tissue. Tobacco mosaic virus was also used for plant genetic transformations, especially in related plants such as tobacco, tomato, and…..petunia. Most of the work I did in undergrad was with the commonly used with model plant Arabidopsis thaliana (mouse-ear cress).

The transformation, or success, rates for these methods was relatively low compared to CRISPR. Plus, where the DNA ended up was random. There was no control over where the new snippets of DNA ended up, or what genes they would disrupt, or knock-out, in the process. I did quite a bit of research as an undergrad on figuring out just what genes were knocked out in certain transformations and what that changed in their physiology or response to stimuli (our research focus was gravitropism and response to red light).

CRISPR has taken away the guessing game from genetic transformations. Scientists can now target exactly where they want genes to be inserted, or in some cases “knocked out” or interrupted so they are not expressed. For example, Arctic Apples were developed by knocking out the gene in apples that makes polyphenol oxidase, the enzyme that causes them to turn brown after cutting. This has created a technology that has the potential to substantially reduce food waste in crops that have similar reactions as well, such as potato.

So I think the trend of genetically engineered plants for consumers will continue to grow. Evolving from novelty plants to plants that serve a higher purposes, such as nutritional value enhancements, climate change resistance, and more. It will take us a while to get there, but as the technology advances so does, it seems, public opinion. Until then, I’ll just enjoy my glowing petunias and purple tomatoes.

Additional Sources

https://www.scientificamerican.com/article/this-genetically-engineered-petunia-glows-in-the-dark-and-could-be-yours-for-29/

https://www.science.org/content/article/mushrooms-give-plants-green-light-glow

https://www.fastcompany.com/91073850/glow-in-the-dark-petunias-are-just-the-beginning

Underrated Beneficial Arthropods Part 3: Nutrient Cyclers

For the third and final installment of the Underrated Beneficial Arthropods series, I will be talking about a group of organisms that is arguably one of the least recognized and most underappreciated when it comes to beneficials. Often doing most of their work ‘behind the scenes’ the nutrient cyclers, more familiarly referred to as decomposers or saprophytes, play a crucial role in our landscapes, one that is equally as important as that of pollinators and natural enemies. Although one of the more famous examples of nutrient cyclers that many gardeners are fond of are earthworms, since these are not arthropods I will not be focusing on them in this post. (I am, however, planning on dedicating an entire post specifically to earthworms, so stay tuned for that).

According to Galente and Marcos-Garcia, 90% of the organic matter produced by green plants in terrestrial ecosystems is not consumed. The arthropods in this category provide essential ecosystem services by breaking down materials such as waste, dead plants and animals and redistributing nutrients in the soil and making them available to the plants and other primary producers (which is why they are referred to as ‘nutrient cyclers’). Although it’s not a very glamorous job nutrient cycling is essential to a well-functioning ecosystem, without which, the earth would be covered in dead plants and animals.

Dung Beetles. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Like the previous posts in this series, I will be organizing this post by group of arthropods, and highlighting some of the most notable examples of nutrient cyclers in each group. This will not be an exhaustive list of all the nutrient cycling arthropods but I will include resources at the end if you want to continue to explore this topic further.

Beetles

Containing dead plant, dung and carrion (decaying animals) feeding groups, beetles (Order: Coleoptera) run the gamut of nutrient cycling roles. Some of the most well-known in this group include the charismatic black and yellow or orange carrion beetles and burying beetles (Family: Silphidae) who bury small animal carcasses into the soil, lay their eggs on them, and allow their larvae to feed on the carcasses.

American Carrion Beetle (Necrophila americana). Photo: Abiya Saeed

Other well-known decomposers in this group include dung beetles (Family: Scarabaeidae) which consume the feces of other animals. Due to the fact that these dung beetles process a significant amount of cattle dung and contribute greatly to the reduction of fouled forage from the accumulation of dung in livestock landscapes, Losey and Vaughan (2006) estimated the financial value of this reduction of forage fouling to be $122 million. They also play a significant role in reducing the amount of nitrogen lost to the atmosphere if dung was left on the surface to dry. By burying this dung the nitrogen is integrated into the soil making it available to plants. Sap beetles (Family: Nitidulidae) are just one example of beetles that feed on a variety of overripe, damaged, or decomposing fruit and vegetation (which may be a context that many gardeners would see them in). There are also several other beetles that shred dead vegetation such as leaflitter, bore into wood, and help create the layer of organic matter (humus) on the soil surface.

Burying Beetle (Nicrophorus investigator). Photo: Joseph Berger, Bugwood.org

Flies

Flies (Order: Diptera) also contain all the categories of nutrient cyclers- from carrion feeding to decaying vegetation and waste. Some of the most famous flies in this category are the ones that play an important role in decomposing carcasses and, as such, are important in forensic entomology. Blow flies (Family: Calliphoridae) and flesh flies (Family: Sarcophagidae) are two of the most important forensic fly families. Phorid flies (Family: Phoridae) feed on a variety of decaying plants and animals. Crane fly (Family: Tipulidae) aquatic larvae are also well-known decomposers that feed on decaying vegetation and leaf debris. Although a few species of fruit flies (Family: Drosophilidae and Tephritidae) can be important agricultural pests, other species in this group feed primarily on rotting fruit. When indoors many of these groups of flies can be a nuisance and also transmit bacteria from the surfaces on which they were feeding so controlling them in indoors is often important.

Blow Fly (Family: Calliphoridae). Photo: Susan Ellis, Bugwood.org

Cockroaches

Cockroaches (Order: Blattodea) often get painted with a broad brush as ‘pests or vermin’, however of the approximately 4000 species of cockroaches in the world less than 1% are considered pests of any kind. As omnivores, cockroaches can feed on a variety of materials, but many within this group are detritivores (feeding on decaying vegetation). Most of these beneficial species of cockroaches are found in leaflitter and moist areas with rich organic matter outdoors and are rarely going to enter your house, and if they do happen to get inside are only considered a minor nuisance. A well-known group of these decomposers is referred to as wood cockroaches or wood roaches.

Wood roach (Parcoblatta spp.). Photo: Kansas Department of Agriculture , Bugwood.org

Termites

Formerly in their own order (Isoptera), termites now belong to the same order as cockroaches (Blattodea) due to molecular evidence that indicates that they may have evolved from within the lineage of cockroaches. Like their cockroach relatives, these organisms often have a negative reputation since a few species of termites can be major structural pests with a significant economic impact. That being said, less than 10% of the over 2750 species of termites have been recorded as pests. The rest of this group can have significant benefits due to their feeding biology. Termites are one of the few animals that can break down cellulose (due to symbiotic associations with microorganisms in their gut) which plays an important role in helping to decompose dead woody vegetation, especially in the tropics where termites are also most abundant.  

Eastern subterranean termite (Reticulitermes flavipes). Photo: Phil Sloderbeck, Kansas State University, Bugwood.org

Springtails

Globular springtail (Sminthurus spp.). Photo: Joseph Berger, Bugwood.org

Springtails (Order: Collembola) are a group of impossibly adorable hexapods (six-legged organisms) but they are not considered insects. These tiny critters are found in moist environments and feed on decaying organic matter, decomposing plant materials, and fungi. They are called springtails because many in this group have a forked structure (furcula) folded under their abdomen that they can deploy to flick them upwards. If you haven’t yet seen this in action, I would strongly encourage you to check out some of the awesome YouTube videos that showcase this very cool function. These organisms are harmless to people and pets, and can easily be managed in indoor settings by reducing the moisture. Some of the most famous springtails include snow fleas which are noticeable tiny creatures aggregating on top of snow on warm sunny days.

Springtails (Entomobrya unostrigata). Photo: Joseph Berger, Bugwood.org

Isopods

Isopods (Order: Isopoda) are an order of Crustaceans that contain both aquatic and terrestrial organisms called woodlice. Of the nearly 10,000 species found worldwide about half of them are terrestrial. More affectionately referred to as pill bugs or roly-poly bugs (due to the fact that many can roll into a ball when disturbed), every child and adult has likely experienced these land isopods in an outdoor setting. They can be found in moist and dark environments such as under logs, rocks, and leaflitter. Like termites, Isopods also have symbiotic microorganisms which allow them to digest cellulose. As they break down decaying vegetation, they help improve soil quality, and make nutrients available for plant growth.

Pillbug (Order: Isopoda). Photo: David Cappaert, Bugwood.org

Millipedes

Millipedes (Class: Diplopoda) are a familiar and easily recognizable garden companion for a lot of us. These many-legged arthropods can be distinguished from their carnivorous cousins (Centipedes, Class: Chilopoda) by the number of legs per body segment. Where centipedes have 1 pair of legs per body segment, millipedes have 2 pairs (4 legs) per segment. Unlike their name suggests, they do not have 1000 legs, but a majority of the nearly 10,000 estimated species of millipedes fall within the range of 40 to 400 legs. Like many nutrient cyclers, they are found in damp environments where they feed on decaying vegetation and are important in making nutrients available to primary producers in the landscape.

American Giant Millipede (Narceus americanus). Photo: Abiya Saeed

Mites

Mites (Subclass: Acari) contain a variety of organisms that include predators and decomposers. The estimated 50,000 species of mites worldwide are fairly understudied with scientists pointing towards a potential million species that have yet to be described in this group. Oribatid mites (Order: Oribatida) in particular are key detritivores found in the top layers of soil. According to a SARE publication, they are so abundant, that a 100 gram sample of soil can contain as many as 500 individuals within 100 different genera. In fact, one of my first arthropod-related jobs was working as a lab technician on a subarctic soil mite biodiversity study where I had to sift through soil samples and photograph thousands of these nearly microscopic mites. These tiny ‘microarthropods’ are critical in breaking down leaflitter into smaller pieces which can then be further decomposed by smaller organisms. They also stimulate microbial activity by dispersing bacteria and fungi, which plays a very significant role in soil turnover.

Oribatid Mite. Photo: S.E. Thorpe.

There are many other groups of decomposers that can be found in a variety of different arthropod classes and orders but, unfortunately, the information on this topic is not as easy to find as that on pollinators and natural enemies. Although it is not a very glamorous job nutrient cyclers are critical in maintaining a healthy ecosystem by breaking down waste (such as feces, carcasses, and dead vegetation) and improving soil structure, function, and nutrient availability either directly or indirectly through their various biological functions. I hope you enjoyed learning about them as much as I did, and I especially hope that you will consider the various roles that arthropods play within their ecosystems the next time you see a familiar or unfamiliar critter in your gardens.

Resources:

Losey, J. E., & Vaughan, M. (2006). The economic value of ecological services provided by insects. Bioscience, 56(4), 311-323.
https://academic.oup.com/bioscience/article/56/4/311/229003

Decomposer insects (By: Galente and Marcos-Garcia):
https://entnemdept.ufl.edu/capinera/eny5236/pest1/content/03/2_decomposers.pdf

Burying Beetles:
https://entomology.umn.edu/burying-beetles

Dung Beetles:
https://extension.umaine.edu/blueberries/factsheets/insects/194-beneficial-insect-series-3-dung-beetles/

Sap Beetles:
https://extension.umn.edu/yard-and-garden-insects/sap-beetles

Blow Flies and Flesh Flies:
https://yardandgarden.extension.iastate.edu/encyclopedia/blow-and-flesh-flies

Wood cockroaches:
https://extension.psu.edu/wood-cockroaches

Springtails:
https://mdc.mo.gov/discover-nature/field-guide/springtails

Isopods:
https://mdc.mo.gov/discover-nature/field-guide/pillbugs-sowbugs-land-isopods

Millipedes:
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2345&context=extension_curall

Oribatid Mites:
https://www.sare.org/publications/farming-with-soil-life/mesofauna-arthropods/

People and Plants

It’s time for our Spring edition of People and Plants. This time we’ll be taking a look at the life and accomplishments of Asa Gray.

Asa Gray in 1864
CC image

Asa Gray (November 18, 1810 – January 30, 1888), now considered the most important American botanist of the 19th century, had very humble beginnings. He was born in the back of his father’s tannery in Sauquoit, New York, the eldest of eight children. From childhood Asa was an avid reader. After completing grammar school in 1825 he attended the Fairfield Academy in Herkimer Co., New York and then went on to the Fairfield Medical College in 1826. It was then he began mounting botanical specimens. He got his medical degree and did eventually open a practise in Bridgewater, New York but never really “made a go of it”, he enjoyed botany much more. So much more that in the fall of 1831 he basically gave up his medical practise to devote more time to the study of plants.

By 1832 he was trading specimens with botanists not only in America but also in the Pacific Islands, Asia and Europe.
In early 1836 he became curator and librarian at the Lyceum of Natural History in New York, now called the New York Academy of Sciences, he resigned in 1837. In 1838 he took a position at the newly established University of Michigan as the Appointed Professor of Botany and Zoology. This position was the first devoted solely to botany at any educational institution in America. He was soon dispatched to Europe to purchase books to start the university’s library and for equipment, such as microscopes, to aid research. He spent a year traveling around Europe, visiting gardens and meeting important botanists of the day including William Hooker in Glasgow, Jospeh Descaisne in Paris, Stephan Endlicher in Vienna, and Augustin Pyramus de Candolle in Geneva. He returned to the USA in 1841.
Some trip, eh?

Gray in 1841
CC image

While he was in Paris at the Jardin des Plantes Gray came across an unnamed dried specimen, collected by André Michaux, and named it Shortia galacifolia. Over the next 38 years he spent considerable effort looking for a specimen in the wild. The first expedition in the summer of 1841 to an area in Ashe Co., North Carolina was unsuccessful. Further expeditions yielded the same negative results. In May 1877 a North Carolina herb collector found a plant he couldn’t identify. It was collected and sent to Joseph Whipple Congdon who contacted Gray telling him that he felt he’d found Shortia. Gray was thrilled to confirm this when he saw the specimen in October 1878. In spring 1879 Gray led an expedition to the spot where S. galacifolia had been found. Unfortunately, and much to his disappointment, Gray never saw the wild species in bloom.

Shortia galacifolia – 2013. Photographed in Oconee County, South Carolina.
CC image

In 1841 Gray was elected to the American Academy of Arts and Sciences. In 1842 he accepted the offer of a position at Harvard University. It included a salary of $1,000/year, teaching only botany, and being the superintendent of Harvard’s botanic garden. Though the salary was low the position allowed him plenty of time to do research and work in the garden. He was only 32.
At the time he had a priceless collection of more than 200,000 preserved plants, many of which he named as new species, and 2,000 botanical texts, which he donated to Harvard to found its botany department.

Asa Gray, the early years at Harvard
CC image

In the summer of 1844 Gray moved into what became known as the Asa Gray House in the Botanic Garden. As an academic, Gray was considered a weak lecturer but was highly regarded by his peers for his expert knowledge. He was better suited to teaching advanced rather than introductory classes, which he found tedious.
He eventually became well known by the outside of academia for his prolific writings and textbooks.

Asa Gray House

His first book, The Elements of Botany was published in 1836. In it Gray championed the idea that botany was useful not only to medicine, but also for farmers. His next work Flora of North America, co-authored with John Torrey, was published in 1938.
By the mid-1850s he had become so well-known that he wrote two high school-level texts in the late 1850s: First Lessons in Botany and Vegetable Physiology (1857) and How Plants Grow: A Simple Introduction to Structural Botany (1858). The publishers pressured Gray to make these two books non-technical enough so high school students and non-scientists could understand them.
A prolific writer, he was instrumental in unifying the taxonomy of North American plants. The most popular book was his Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive, known today simply as Gray’s Manual. Gray was the sole author of the first five editions of the book and co-author of the sixth, with botanical illustrations by Isaac Sprague. Many editions have been published and it remains a standard in the field. 

Illustration from Gray’s Manual of the Botany of the Northern United States

Gray also worked extensively on a phenomenon called the “Asa Gray disjunction” which is the surprising morphological similarities between many eastern Asian and eastern North American plants.

Before 1840 Gray’s knowledge of Western US plants was limited to specimens sent him by collectors and colleagues working in the field. He worked with George Engelmann, Ferdinand Lindheimer, and Charles Wright who all collected widely in the Southwest including Texas, New Mexico, and parts of northern Mexico.
Accompanied by his wife, Gray finally traveled to the American West on two separate occasions, the first by train in 1872  and then again in 1877. Both times his goal was botanical research and sample collection to take back to Harvard. His collecting companion on these trips was Jospeh Dalton Hooker, son of William Hooker whom Gray had met in Glasgow on his first trip to Europe in 1838. Gray’s and Hooker’s research was reported in their joint 1880 publication, “The Vegetation of the Rocky Mountain Region and a Comparison with that of Other Parts of the World,” which appeared in volume six of Hayden’s Bulletin of the United States Geological and Geophysical Survey of the Territories.

Asa died in January of 1888 after suffering a stroke two months prior.

Aesculus discolor by Gray, from Plates Prepared between the Years 1849 and 1859 to Accompany a Report on the Forest Trees of North America
Public domain image

We’ve just skipped a stone across the pond of Asa Gray’s life. Here are some links if you’d like to learn more.
Asa at 200 –https://huh.harvard.edu/book/asa-gray-200
The Asa Gray Bulletin – https://www.jstor.org/journal/asagraybull
Asa Gray: Faith and Evolution – https://sciencemeetsfaith.wordpress.com/2020/11/17/asa-gray-bridging-faith-and-evolution/
Asa Gray online papers – https://onlinebooks.library.upenn.edu/webbin/book/lookupname?key=Gray%2C%20Asa%2C%201810%2D1888
Asa Gray Award – https://www.aspt.net/asa-gray-award

What we expect in the 2024 growing season

As I write this, about half of the lower 48 United States has passed the median date of the last freeze according to the National Centers for Environmental Information. Here in the Southeast, we are well into the planting season even though our usually early planting for crops like corn was delayed due to very wet soil. The rest of you may have to wait for a few more weeks before you can put any heat-loving plants into the ground. As we enter the growing season for the majority of the country I thought it might be helpful to take an updated look at what we expect this summer and fall to give you an idea of what conditions you might experience.

Bluebonnets. Source: Willwpn10, Commons Wikimedia.

What factors will control the climate this summer?

In the Southeast most gardeners say that you should not plant summer crops and flowers until after Easter, although since Easter has a variable date that can sometimes be a problem when it is unusually early. In western Michigan where I grew up my grandmother always told me to wait until after Memorial Day. What rule of thumb do you use? If you look at the map below, you can see why! Wherever you garden you need to know the specific weather and climate to expect in your location. That includes things like the plant hardiness zone, how much rain to expect, and the specific microclimates within your garden (especially if it is a large one). That will help you pick the plants and trees that will do best in your location.

Every year is unique in terms of what temperature and precipitation patterns occur, but in many parts of the country we can get some indications of what might occur due to large-scale climate patterns that are occurring across the world. Of course these also affect the weather in other places from Europe to Australia and points in between, but I am going to focus on the US in this post.

The biggest patterns that are going to be affecting the climate this summer include 1) rising temperatures due to greenhouse warming, 2) the predicted transition from a strong El Niño to a La Niña later this summer, and 3) unusual warmth in the Atlantic Ocean which will affect the development of tropical storms and hurricanes in this year’s Atlantic Tropical Season.

Impacts of greenhouse warming trend

As temperatures rises around the globe we can expect both daytime high temperatures and overnight low temperatures to increase in temperature. In most areas the minimum overnight temperatures are rising faster than the daytime highs. This is due to a combination of increased humidity caused by increases in evaporation and more water-holding capacity of the air and heat-trapping in urban areas due to pavement and buildings. You can determine trends in temperature and precipitation for your location using the “Climate at a Glance” tool for anywhere in the continental US, including maximum and minimum temperature. The increased humidity will increase the likelihood of fungal diseases in plants that are susceptible so you will want to watch carefully and be prepared to treat them. You should also watch for protracted hot, dry spells and increased water usage, which might require you to water more often. But keep in mind that while the average temperature might be warmer, there will still be ups and downs with the daily weather.

Source: Albarubescens , Commons Wikimedia

Impacts of El Niño swinging to La Niña

We are currently in a waning El Niño (EN) after experiencing a strong EN over the winter. The winter weather pattern showed a very clear EN pattern over most of the country (and other parts of the world for that matter) with unusual warmth and dry conditions in the northern US and wet, somewhat cooler, cloudier conditions in the southern part of the country although that was tempered by the long-term temperature trend upward. The current EN is expected to disappear rapidly over the next few months and swing to the opposite phase, La Niña (LN), by mid to late summer as shown below. I also discussed this back in February. This LN will likely control our weather for a good part of the rest of 2024 and into the spring of 2025.

Source: https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

How will this affect the growing season weather in the US? While the correlation between LN or EN and summer weather is less strong than the winter correlation, we do expect to see some lingering effects of EN for the next few months before LN kicks in. That means wetter conditions are likely to continue in the southeastern US for the next few months before dry and sunny conditions move in later this summer or fall. The timing of when that transition occurs depends on how quickly the transition from EN to LN occurs. It is changing right now, but it’s still too early to tell how soon it will affect our summer weather. In the northern US we will probably see more seasonal weather for the next few months but next winter is likely to be much colder and wetter than last year. Again, the transition should occur later this summer but could wait until late fall to really become apparent. Some areas like the Central Plains are not very predictable by the phase of EN or LN so we are less certain about what you will experience if you live there. You can see the lack of certainty in the May-July temperature map below.

The warm Atlantic and what we expect from the Atlantic tropics this year

Last year, we had 19 named storms plus three other unnamed storms that were close to tropical status. This is in spite of the El Niño, which usually suppresses development of tropical systems because of strong winds aloft that keep tropical storms from developing the vertical structure they need to grow. Most of those storms stayed over the Atlantic Ocean where the water temperatures have been at record-setting levels for over a year. They are still at record-setting levels now and are even hotter than last year at this time. This year with a La Niña there is not much to keep storms from developing so I expect to see more storms, especially in the western Atlantic and in the Gulf, where they are more likely to come onshore and do damage or drop a lot of rain along their paths. I have seen predictions of as many as 33 named storms this year, although that would be a record and climatologists don’t generally like to forecast record values. A more conservative value of mid-20s for named storms seems more likely, although this is still a lot more than we usually get. What you actually experience depends critically on the path that the storms take, which cannot be predicted until after the storms form. So you could get hit directly by strong winds and heavy rain or you could be in the area outside the path with clear skies, sinking air, and no rain at all.

No matter how many named storms we get, those of you who live in the eastern US where a hurricane or tropical storm (or their remnants, which can also carry flooding rain to places far away from the tropics) can travel should be watching carefully when the storms start popping later this spring or early summer. Conversely if you live in the western US, you may see less activity this year than last year since when LN is strong, the Eastern Pacific Ocean (EPO) storms have a harder time developing due to the colder ocean water in the EPO associated with LN. But with rising global temperatures we are in uncharted territory so surprises are always possible.

What NOAA’s Climate Prediction Center predicts

The combination of all of these factors (and other climate influences as well) is collected into NOAA’s Climate Prediction Center maps. I have shown the one for May through July 2024 below. It shows the likelihood of wet conditions in the Southeast and drier conditions out west associated with the lagging EN conditions. You can see maps for other time periods at Climate Prediction Center – Seasonal Outlook (noaa.gov).

For gardeners, if you are in the region where frost is still likely, you should hold off on planting tender vegetables and flowers at this point or at least start them inside. If you are in the southern reaches where frost is no longer likely then you can (and probably are already) plant the summer flowers and vegetables you are craving to set out, as long as no cold outbreaks are predicted. If you live in an area that is affected either directly by tropical storms and hurricanes or indirectly by heavy rains that remain after the storm has weakened now is a good time to clear out dead limbs and other potential flying debris, think about drainage in your gardens in case of heavy rain. Please make your hurricane plans in case one tracks over you (you can find one for Georgia at https://gacoast.uga.edu/wp-content/uploads/2020/08/ResidentsHandbook.pdf but most of the information there is relevant to large parts of the country). If you live in other parts of the country like the western states, you could see dry conditions and potential wildfires return to those areas so you should prepare for those conditions. By late fall, the La Niña should be well established and dry conditions are likely to occur in the southern tier of the US while cold and wet conditions are more likely in the northern states.

Spring with flowers. Source: Larisa Koshkina, Commons Wikimedia.

This bud (removal) is for you: Does early flower removal aid plant establishment in fruiting plants like tomatoes?

In many publications and garden resources you see the suggestion to remove flower buds to improve establishment of new fruit and vegetable plants. This advice is shared for both woody and perennial plants like fruit trees and strawberries and for annuals like tomatoes and peppers. And whenever you see someone stating this as gospel, you see someone else stating that it is false or only anecdotal. So the question is – does research support the advice to remove early plant blossoms to improve vegetative plant growth and establishment? Let’s take a look at some recent, and not so recent, research to see what really happens and understand the process.

The Physiological Process

Prior to my extension career teaching people gardening, I fancied myself a budding (ha ha) plant science researcher. Many of my classes, therefore, were focused on plant physiology and genetics. Not necessarily handy in teaching people the basics of gardening, but pretty damn handy in explaining how plant processes work.

As most upper elementary and middle school students will tell you, plants make their own food in the form of the sugar glucose by using energy from the sun through photosynthesis. That glucose is used in the respiration process to release the energy for the plant to use, transformed into other sugars and compounds for functions around the plant, or turned into starch for long-term storage. Photosynthesis is not an unlimited process and genetics, environment, and other factors play a role in the rate of energy development. So it stands to reason that there are lots of things that have to happen with the finite resources made by the plant.

In plant physiology circles, photosynthesis is called the “source” of plant energy and those uses, such as root, leaf, stem, wood, flower, and fruit production and storage are called “sinks” (sometimes also “pools”). Researchers often discuss these pathways as “source-sink” interactions. Since there are only so many carbohydrates to go around, researchers have long known that when demand is high for growth of certain structures that development of other structures is slowed. If there is a period of rapid root growth, the demand for carbohydrates in the roots increases and the availability for other locations in the plant is decreased. As a result growth in the leaves, stems, or reproductive organs may slow until a supply is restored. But this phenomenon varies by plant species and even cultivar/type, as genetics does play a role in the rate of photosynthesis. Some plants have a higher level of photosynthesis to help offset the sudden upswing of need, and some don’t.

Source: Michael G Ryan, Ram Oren, Richard H Waring, Fruiting and sink competition, Tree Physiology, Volume 38, Issue 9, September 2018, Pages 1261–1266

Think of it like a household budget, but you have a job that only pays you in months that are warm and sunny. You have a set monthly income (the source) and then your housing, utilities, food, and other bills to pay (the sinks). Plus, hopefully you are saving some money for later somehow (another sink). If your bill sinks are greater than your income source, you might dip into your savings a bit, but you don’t want to take it all because you will need most of it in the months when you don’t get paid because it is cold and dreary, or your leaves have fallen off, or your herbaceous bits have died back. As a plant you don’t qualify for credit so the only way to make things work is to cut back in some areas (a sad reality for many on limited incomes). You have to reduce your utility usage, cut back on more expensive foods, find cheaper rent, etc. Similarly, a plant has to reduce the amount of energy used for, say, root growth if it has a rapid leaf growth.

And if you have a kid then the expenses go way up, right? That’s what happens when a plant is just minding its business, enjoying a free and frivolous lifestyle when all of a sudden reproduction comes along. First flower structure development, then fruit development. Plants that have a higher rate of photosynthesis have a higher budget to pull from, so the change may be minimal. But when photosynthesis rates are low, like in newly developing plants with few leaves, unfavorable environments, or genetic limits, the effect can be significant.

So, what about my plant?

The question we always get is, “is it necessary to remove the early blossoms on my ______ plant to help it get established?” For perennials like fruit trees, that would generally be the first few years. For annuals like tomatoes, it would be removing blossoms the first few weeks after planting (and removing any blossoms developed before transplanting).  The answer is…maybe. Or more like, there probably is an effect, but it depends on the plant and environment as to how impactful the effect is. This phenomenon has been observed in several species, including Douglas fir, peaches, olives, and more.

For example, research shows that letting blueberry bushes fruit the first two years after planting (not removing flowers or fruits) reduces the biomass (vegetative growth) AND the yield in year 3. The plants will likely catch up in later years, but if your goal is to get plants established early and have fuller harvests sooner, removing flowers in years 1 and 2 would be advisable.

The same can be said for strawberries. The abstract from this paper from 1953 (I couldn’t track down the full article prior to publication) says that “removal of blossom from newly set strawberry plants helps more in the establishment of a vigorous planting than almost any other cultural operation.” This paper doesn’t measure biomass, but did find that removing flowers on day-neutral strawberries (that produce throughout the growing season) until July 1 resulted in maximized yields in the later season and removal of flowers for the entirety of the first year resulted in maximized yields in year 2 (note: in commercial strawberry production, strawberries are usually grown as an annual or at most a biennial, so maximizing early yields is important).

Now, for the all important tomato (drumroll, please). This study from the 70s found that removal of early blooms on indeterminate tomato plants resulted in larger plants (higher vegetative growth) and that eventually the fruit yield nearly caught up with the controls. They found that when fruit development started, leaf growth was “markedly depressed” and root growth ceased (and there was even some root death). So while there was ultimately a small loss of yield, the result was a better established plant that would likely be able to better weather environmental and disease issues throughout the season.

And beyond establishment, flower and/or fruit thinning on plants with high floral numbers has been shown in many plants (apples, blueberries, peaches, and tomatoes, to name a few) to result in larger, higher quality fruits. The same pathways apply here – each and every fruit is a sink. The more sinks you have, the more “mouths” the plant has to feed. So flower removal is a viable production strategy for many different crops and something that home gardeners should think about if you want the biggest, and juiciest fruits on the block.

Sources:

  • Chanana, Y. R., et al. “Effect of flowers and fruit thinning on maturity, yield and quality in peach (Prunus persica Batsch).” Indian Journal of Horticulture 55.4 (1998): 323-326.
  • Dejong, Theodore M., and Yaffa L. Grossman. “Quantifying sink and source limitations on dry matter partitioning to fruit growth in peach trees.” Physiologia Plantarum 95.3 (1995): 437-443.
  • Eis, S., E. H. Garman, and L. F. Ebell. “Relation between cone production and diameter increment of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), grand fir (Abies grandis (Dougl.) Lindl.), and western white pine (Pinus monticola Dougl.).” Canadian Journal of Botany 43.12 (1965): 1553-1559.
  • Hesami, Abdolali, Saadat Sarikhani Khorami, and Seyedeh Samaneh Hosseini. “Effect of shoot pruning and flower thinning on quality and quantity of semi-determinate tomato (Lycopersicon esculentum Mill.).” Notulae Scientia Biologicae 4.1 (2012): 108-111.
  • Hurd, R. G., A. P. Gay, and A. C. Mountifield. “The effect of partial flower removal on the relation betwen root, shootand fruti growth in the indeterminate tomato.” Annals of Applied Biology 93.1 (1979): 77-89.
  • Kim, Jin-Gook, et al. “Effects of cluster and flower thinning on yield and fruit quality in highbush’Jersey’blueberry.” Journal of Bio-Environment Control 19.4 (2010): 392-396.
  • Link, H. “Significance of flower and fruit thinning on fruit quality.” Plant growth regulation 31 (2000): 17-26.
  • Michael G Ryan, Ram Oren, Richard H Waring, Fruiting and sink competition, Tree Physiology, Volume 38, Issue 9, September 2018, Pages 1261–1266, https://doi.org/10.1093/treephys/tpy114
  • Rosati, Adolfo, et al. “Fruit production and branching density affect shoot and whole-tree wood to leaf biomass ratio in olive.” Tree Physiology 38.9 (2018): 1278-1285.
  • Scott, D. H., and P. C. Marth. “Effect of blossom removal on growth of newly set strawberry plants.” (1953): 255-6.
  • Solomakhin, Alexey A., and Michael M. Blanke. “Mechanical flower thinning improves the fruit quality of apples.” Journal of the Science of Food and Agriculture 90.5 (2010): 735-741.
  • Williamson, Jeffrey G., and D. Scott NeSmith. “Evaluation of flower bud removal treatments on growth of young blueberry plants.” Hortscience 42.3 (2007): 571-573.