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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.

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.

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!

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 (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?

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.

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.

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.

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. 

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.

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

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.

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.

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.

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.

Arborists are trained in seminars and texts that rot in trees is bad. Wood decay can constitute a “hazardous condition” which when accompanied by the tree being in a place that has a target and the tree is large, can create a “hazardous tree”. The notion of hazardous trees is a uniquely human construct that has little to do with the ecology of trees, the variety of organisms that utilizes large declining trees, and does not consider what the various defects in trees may be contributing to the environment or forest around that tree in terms of organism habitat.  Humans require that trees living near them must perform appropriately otherwise get out the chain saw and make them comply.   In the last decade tree care for birds and  wildlife has become a popular training subject for arborists in the western United States.  In Europe researchers have been popularizing the notion that large trees can become centers of biodiversity because they have many microhabitats that support numerous organisms not found on younger trees.  This concept is abbreviated TreM or Tree related Microhabitat.

As trees mature and then decline, they accumulate deadwood, cavities, epiphytic organisms, excrescences, exudates, fungal decay organisms, and even accumulates of soil or pockets of water in branch crotches. Arboriculture practice tends to regard tree defects as having no value, thus we remove dead wood, cut down trees with cavities and condemn trees with wood decay sporophores. It is now accepted that the more “defects” a tree accumulates the quantity and diversity of organisms associated with that individual tree also increases. In this sense old trees become centers of biodiversity within both managed and unmanaged forests.

The health of a forest is not measured only by the quality of the wood it can produce or the number of board feet it can supply, but also by its connections to other organisms that ensure its health over time. Forests are ecosystems and require connections between organisms and diversity of organisms in order to be resilient. These organisms utilize not only living but also dying and declining trees. Ancient trees are often rich in defects and have many TreM’s.

Tree injuries such as storm damaged branches, lightning scars, frost cracks, branch failures and and other damage are all considered TreM’s. While these are functional habitat in forests they may be quickly removed from the urban forest even if they do not pose a hazard. Now that they have apparent value, perhaps we can rethink their removal where and when appropriate.

The TreM concept is derived from trees growing in forests not those in cities. TreM’s may not become a management tool for urban forestry, however there are many lessons to be learned from the TreM concept. The greater the number of microhabitats, the more organisms and connections between organisms there will be. This provides resilience even to urban ecosystems. There is strong evidence that TreM’s serve as a reservoir of organisms in forests helping to maintain their health. Using the TreM concept for non-forest trees will not change how trees are managed for many situations. Risk tolerance often trumps ecosystem services. Greater understanding of TreM’s will perhaps allow us to save trees that do not pose hazards where they would otherwise be disposed of. Some tree managers have tried to create defects in trees to enhance habitat for wildlife. This is not based in science and I do not advocate creating TreM’s for the sake of having them in trees. Fungi and other organisms find their way into trees all too easily. Until we have some science based evidence for the creation of TreM’s, I recommend against it. It’s the whole do no harm thing we have going as plant pathologists. Being aware of TreM’s and evaluating their usefulness in the urban forest is a new area of study.

In their field guide, Butler et al., 2020 describe 47 TreM’s that they further break down into 15 groups and 7 types. The field guide is available on line if you want to find out more about TreM’s. The research on TreM’s is nascent, and restricted mainly to Europe and Canada. This fall we will collect data in the Chiricahua Mountains to add to that body of research as part of the South Western Research Station’s Trees Course to be held the last week of September into early October.

References

Butler, R., T. Lachat, F. Krumm, D. Kraus, and L. Larrieu. 2020. Field guide to Tree-related Microhabitats. Descritpions and size limits for their inventory. Birmensdorf, Swiss Federal Insitute for Forest, Snow and Landscape Research WSL. 59 p. www.wsl.ch/fg-trems

Larrieu, L., Paillet, Y., Winter, S., Butler, R., Kraus, D., Krumm, F., Lachat, T., Michel, A.K., Regenery, B., and Vanderkerkhove, K. 2018 Tree related microhabitats in temperate and Mediterranean European forests: a hierarchical typology fr inventory standardization. Ecologial Indicators, 84: 194-207

In the last week, I’ve driven all the way from western Virginia, where the redbuds are blooming, to Tallahassee, FL, where red clover is everywhere. As I drove through the mountains north of Charlotte NC, I noticed some signs indicating that strong gap winds may blow down the valleys when atmospheric pressure patterns align to produce strong pressure gradients that drive the wind. I have discussed wind before in previous posts (“Who has seen the wind?” and “Does wind chill affect plants?”) so you can find the basics of what causes wind and some of the different kinds of local winds by going to those posts. In today’s article I want to share some different local names for winds and other local weather and invite you to share your own local weather names. Note that this is not a complete list, but I will provide links at the end that prove a bigger sample of all the names that are used around the world to denote different kinds of weather, especially wind.

Local weather names based on topography

Local mountains and valleys can cause a big variety in the types of winds we observe. Generally, these winds can be classified as katabatic winds blowing downhill and anabatic winds blowing uphill. The direction depends on the time of day due to heating but also to large-scale weather patterns that direct the flow of air. Local winds can also occur due to changes in the heights of the ridges so that where the ridges are low, air can spill over the mountains in the gaps between peaks. Winds blowing downslope can also accelerate as they move to lower elevations, increasing their strength. Those winds can be very strong because of the funneling effect of the terrain leading to warnings like the ones I saw on Interstate 77 in the northern North Carolina Mountains. Some of these local winds in other parts of the world are called the Viento Zonda (or Zonda wind) in Argentina, the Williwaw in the Alaskan Panhandle, Karaburan in Central Asia, Chinook wind along the Front Range of the Rocky Mountains in the USA, Mistral in France, and the Warm Braw in the Schouten Islands north of New Guinea. You can read more about each of these by looking online at Wikipedia or other sites (link below). Winds which are affected by topography can provide good sources of steady wind for wind farms.

One of the most interesting large-scale topography-driven winds is the Tehuantepecer in southern Mexico which begins in the Gulf of Mexico (after coming south across North America) as a north wind that crosses the Mexican isthmus and blows through the gap between the Mexican and Guatamalan Mountains. It is so strong that it can be felt as much as 100 miles out to sea. This happens several times a year, especially in winter when the wind is more often from the north, and is amazing to see on https://earth.nullschool.net/ when it happens. In fact, as I am writing this on Thursday (March 28, 2024) it is happening today! How cool is that?

Local weather names based on changes of air mass

Some winds are named for abrupt shifts in atmospheric temperature and humidity when air from a different source region moves in. They can be small-scale changes due to outflows from individual thunderstorms like gust fronts or can be larger-scale changes due to wind blowing an air mass with colder, hotter, or drier characteristics into the area.

Some of the winds associated with drier and dustier conditions occur near desert locations as the wind shifts to bring in air from the desert regions to replace the air that was already there. One of the most common terms for one of these is haboob, which originated in Sudan but is now used in the western U. S. (Haboob basically means “dust storm” in Arabic but sounds a lot more exotic). A haboob is associated with a wall of hot, dusty air that moves into the region from the desert, bringing low visibilities to the region (often resulting in car accidents as drivers caught unawares can be blinded by the sudden change in conditions). Other dry winds include the Khamsin in Egypt and the Red Sea region, the Scirocco in North Africa and the Mediterranean, and the Harmattan in West Africa.

Cold winds include the Blue Norther, a fast-moving cold front that moves in from the north that can send temperature plummeting by 20-30 degrees in a few minutes, the Bora in the Adriatic region, the Khazri in the north Caspian Sea, the Montreal Express in New England, and the Norte in Mexico. In the Southeast US, we have what we call the Wedge, which is a shallow layer of cold air that moves south along the eastern slope of the Appalachian Mountains under northeast flow, bringing clouds, cold weather, and the chance of ice storms to the region in spring. The Wedge is partly due to topography as well, since the cold air is so shallow that it can’t move west over the Appalachian Mountains and thus is forced down to us in parts of the Carolinas and Georgia. Hot dry winds include the Brickfielder in southern Australia, the Leveche in southern Spain, and the Diablo and Santa Ana winds in California, which are also affected by air moving down from the mountains into coastal areas of the state when high pressure dominates the Southwest.

Local winds are associated with thunderstorms

In addition to the wind names associated with topography and change of air quality there are also some names that are tied to smaller weather events like hurricanes and thunderstorms. Those include the Kalbaishakhi in India and Bangladesh, the Bayamo on Cuba’s southern coast, the Pampero in Argentina and Uruguay, the Cordonazo on the west coast of Mexico, and the Borasco in the Mediterranean. Strong winds associated with thunderstorms can cause tremendous damage to gardens, trees, and buildings and can cause problems with flights and road transportation. Since it is spring and we are entering severe weather season for a lot of the US, it’s a good reminder that it does not need to be a tornado to cause significant damage—straight-line winds can be just as severe.

Knowing your local climate is important for gardeners

Anyone who lives for a long time at a location will start to recognize the local weather and climate patterns that govern your local garden conditions. If you are really dedicated, you can even measure these variations. If you know that in certain seasons, you are more likely to experience very dry dusty air, you might consider plants that can survive those conditions with less care. If you live in an area that is subject to frequent strong local winds, you will need to plan your garden to place more wind-resistant plants where the air flow is the strongest or else construct a wind shelter to keep more sensitive plants safe. Buildings can also affect the wind flow and can cause “wind tunnels” where the air is constricted and blows faster in the narrow passage.

Note: For those of you who wonder about the title of this post, Maria (sometimes listed as Mariah) is a fictional wind popularized in “Paint Your Wagon” (Lerner and Lowe, 1951) and by the Kingston Trio (1959). The name may have originated with the 1941 book “Storm” by George R. Stewart according to my colleague Jan Null of Golden Gate Weather Services.

Sources of more local wind information

Here are some websites that have listings of additional local winds, although none of them is a complete list, I am sure.

Wikimedia (with links to most of the individual winds): https://en.wikipedia.org/wiki/List_of_local_winds.

GG Weather: https://ggweather.com/winds.html

U. K. Met Office: https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/wind/wind-names

If you have a local name for the wind or weather in your region, please share it in the comments!

Wherever whitetail deer occur they present a challenge for gardeners. The internet offers abundant advice on this, but too often it is simplistic gardening myth such as scattering human hair or planting garlic.

Historically in deer control literature there have been occasional observations that deer hesitate to enter an area which looks too small or constrained for rapid escape. Finally, it came time to acknowledge and test this theory.

Green Island Preserve and the University of Minnesota Extension set about investigating this possibility through their Regional Sustainable Development Partnership (RSDP) program which provides support to community-benefit projects in partnership with private citizens and organizations. The test site was a 60 acre rewilded forest inside a small northern city. Deer pressure was heavy with resident herd numbers varying from 16-30 animals during the trial.

The first issue was defining a “small space” for testing the theory. In all the literature only one other trial of this concept could be found. It was conducted in Wisconsin with traditionally fenced spaces ranging from 15 ft by 15 ft to 21 ft by 21 ft feet during part of one summer. The Minnesota Green Island Preserve and RSDP trial chose 16 feet by 16 feet based upon the dimensions of manufactured, ridged cattle panels. These panels are 50 inches in height and 16 ft long and tend to be readily available at Fleet or Home stores even in suburban areas. If successful, their advantage would be very easy set-up and portability at a reasonable cost.

What was the result? Over 2 years of trial, this test demonstrated 95% success. Six micro-exclosures were established and planted within forested and forest edge locations in a zone of heavy deer pressure. During an observation period of 730 days, only one instance of deer browse occurred inside a micro-exclosure.

This success rate is more impressive because these fences are not a physical barrier to deer entry. They are strictly a psychological deterrent. This places them in much the same class as flashing lights, sound cannon, water spray, etc., but according to this study’s data, they’re actually more effective. All psychological deterrents have a failure rate dependent on application, monitoring, seasonality, rainfall, and more. But micro-exclosures show a low failure rate, without maintenance. If a deer breach does occur, the solution is simply to make the exclosure appear even smaller. This can be done by stretching rope across the center holding noticeable flagging. It can be lifted off when tending plants.

This is a highly promising discovery which merits further controlled testing by universities and professionals. The Minnesota Green Island Preserve and RSDP trial was specifically targeted to white tail deer predation while other ungulates present browse problems in other geographies. Rabbits were not addressed. However, until further and definitive research is conducted, citizen-scientist gardeners can contribute by testing versions of this method for themselves and adding their data to the general deer-control knowledge base. In using and testing micro-exclosures, gardeners will fare infinitely better than by spreading human hair, interplanting garlic, or buying “ultrasonic” gizmos.

This post was provided by Kent Scheer. Kent is a career sculptor with a side mission for reforestation and environmental compassion. He is the editor of three handbooks on sustainable agriculture resources and owner/ manager of a rewilded pine forest in northern Minnesota created for environmental education and awareness. You can contact Kent at kentscheer@outlook.com.

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

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

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

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

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

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

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

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

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

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

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

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

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

Review—What are El Niño and La Niña?

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

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

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

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

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

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

When will La Niña begin?

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

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

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

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

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

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

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

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/.