I often feel slightly nauseous after a day of debunking misinformation online, in emails, and in person. Others who selflessly give their time and energy to the same efforts probably feel the same. An antidote counteracts poison; in a very real sense, those of us who guide gardeners through the six circles of horticultural hell are routinely exposed to the mind-numbing dregs of lazy thinking.
Not exactly Dante’s Inferno, but this ‘Inferno’ coleus is certainly ablaze. Courtesy of The Blade.
What are the six circles of horticultural hell, you may ask?
After playing with word lists and acronyms I have come up with the ABSURD approach,
as in “don’t be ABSURD with your gardening information.”
This is a first draft of ABSURDity and I imagine it might get tweaked and shaped a bit. But it’s a good mnemonic device for educators to consider using, right along with the CRAP test.
A = anecdotal. Anecdotal evidence is simply one person’s observations that are not supported with scientific evidence. Reporting that your roses grew better when you used compost tea is an anecdote. Anecdotes are often collected by advertisers and called “testimonials” which sounds vaguely legal and therefore more reliable.
B = bogus. Bogus information is verifiably false; factual evidence exists to disprove it. Claiming that water droplets will scorch leaves on hot days is bogus.
There are lots of photos of water drops on leaves, but none that show scorching. Courtesy of pixabay.com.
S = scam. Scammy sources of information exist to sell stuff. Websites selling seeds for nonexistent flowers whose pictures are generated by AI are scammy.
A scam is born…
U = useless. Useless information promotes something that has no effect. Adding eggshells to gardens for any purpose is useless.
At least this photo is from a website with good information! Courtesy of MSU Extension.
R = ridiculous. Ridiculous recommendations defy even common sense. Placing plastic forks into the soil to discourage animals from digging is ridiculous.
Salad fork takes on a whole new meaning.
D = dangerous. Dangerous products and practices can injure people, pets, and the environment. Putting mothballs in your landscape to discourage nuisance wildlife is dangerous.
You can find many more examples of ABSURDities in our 15 years of blog archives. Simply type in the word you are looking for and have fun diving down the (mothball-free) rabbit holes!
Type in a word, or part of a word, to find archived blog posts to explore.
Early in August, Hurricane Debby made landfall in the Big Bend of Florida’s Gulf Coast, crossed into Georgia east of Valdosta, and moved leisurely northeast. The remains of Debby crossed the coast, briefly moved over the Atlantic Ocean before turning northwest and making another landfall northeast of Charleston then headed north into New England. While the winds decreased quickly once Debby made landfall, it dropped huge amounts of rain along its path. The highest official rainfall amounts topped 12 inches, but I heard of some unofficial measurements of 20 inches in a few isolated locations. Pictures of erosion in peanut fields and standing water in cotton stands filled my inbox, and it made me wonder how a garden would cope with so much precipitation in such a short period of time. I want to take a few minutes today to discuss it.
Initial estimate of rain from Hurricane Debby, August 8, 2024.
What damage does the rain do when it hits the ground?
When the falling raindrops hit leaves, they can cause damage
to the plants. The biggest raindrops are heavy and falling fast so they can
break off or damage the foliage, although not as much as hail does. We see this
especially in fall when the leaves are loosely attached to the branches after
they start to change color and die. A
heavy rain (or snow if you live in a colder area) can remove a lot of leaves in
a short time, making the fall colors muted or non-existent as the leaves
are washed to the ground.
When the rain hits bare ground it can cause soil particles and microbes to splash upward. Farmers know that rainy weather can lead to more diseases because of the enhanced transmission of fungal spores and other pathogens up onto the crops. Of course, the wet soils can also provide a lot of moisture in the air around the plants that can fuel the development of fungal diseases like powdery mildew, especially when plants are close together with little ventilation by the wind. Mulch may be able to help reduce the transmission of spores but creates a moist environment around the roots of the plants that can cause problems if it keeps too much water in the ground. One advantage of arborist wood chips is that the wood absorbs moisture and releases it later and the pores between wood chips are large and can store a lot of water before it runs off. It can also preserve soil moisture between rain events and it can reduce the impact of raindrops on the soil surface, limiting nutrient loss and splashing.
Erosion of peanut field in Screven County, GA, following Hurricane Debby, GA Peanut Growers.
Where does the rain go when it hits the ground?
Once rain hits the ground, some of it sinks into the ground (infiltration) while the rest might either run off if there is a slope or stand in a puddle if there is a low-lying or flat area. The rate at which water can enter the soil depends on the characteristics of the soil. If it is gravel or coarse sand, it can take in as much as 0.8 inches of water per hour. Sandy loams can take in 0.4 to 0.8 inches per hour, loams 0.2 to 0.4 inches per hour, and clay soils less than 0.2 inches per hour. The rain can also compact the soil, making the movement of oxygen around the roots more restricted. The water that does not sink into the soils will either sit at the place the rain has fallen or will move downhill under the force of gravity. Flowing water will often carry a lot of soil and debris with it, so the movement of topsoil and nutrients like nitrogen from field to stream can cause problems for both environments. Silt from the floodwaters can cause loss of oxygen in streams and murky conditions affecting the stream health or the silt can be deposited in low-lying areas. In the biggest floods, large deposits of sand can ruin fertile bottomlands by covering healthy soil with thick deposits of unproductive silt and sand. The erosion can also dig deep trenches through gardens and farm fields, leading to loss of plants and making the movement of farm equipment across that rutted land difficult especially since it can also get bogged down in the mud.
If the water pools in a low-lying area the soil can become saturated for a long time. This causes damage to the plants standing in the water because without oxygen, the roots die. In the short term the loss of oxygen can cause the plants to wilt. If it lasts for a long time it is likely to lead to the death of the plants in low-lying areas. In Hurricane Debby, some farmers are starting to see flooded cotton plants become reddish and stop growing, reducing the eventual yield of the crop. The dying roots can also give off ethylene gas, hastening the ripening of crops like tobacco and shortening the time that farmers have to harvest it before it rots. Farmers are often told to harvest crops that grew in flooded areas separately from upland crops because the negative impacts of oxygen deprivation can stunt plants, ruining their yields and increasing the likelihood of aflatoxin in peanuts or other toxins which can decimate the value of the crop.
Partially flooded watermelon field, B. King, The South Carolina Grower.
What can gardeners do to prepare their gardens for heavy
rains?
In the future, the frequency of heavy rains is expected to increase in the United States as well as other parts of the world because of more water vapor in the atmosphere as the planet warms. What can gardeners do to make sure their gardens can withstand heavy rain events? The first thing to do is to understand what type of soil you have and how much water it can absorb. If you have sandy soil, heavy rain will have less of an effect than clay soil but it might mean you have to water a lot more often. In Debby, some areas that received 12 inches of rainfall needed irrigation less than a week after the storm moved through because the sandy soil of the coastal plain just does not hold much water. The next thing you should consider is the local topography of your garden. Are there areas that are natural channels for water? Make sure those areas are lined with material and plants that can withstand water and reduce erosion. If you have low-lying areas, use those to plant rain gardens with plants that are more adapted to wet conditions.
Rain is a necessary part of gardening unless you live in a
desert and provide your own water to your gardens, but it can cause a lot of
damage if the water is not managed carefully. Take the time to study your garden
and understand where the water will flow and your garden will be much more
likely to take a 12-inch rainfall in stride with minimal damage. It might even
thrive!
Landscape of leaves after rain, Arushan, Commons Wikimedia.
A polycultural landscape mixing vineyards and annual crops with woody hedgerows and trees in Charente, France. Photo courtesy of JLPC through Wikimedia.
As gardeners, we often assign human characteristics to our plants as a way of feeling more connected to them. We talk about their preferences and dislikes for certain environmental conditions and even for each other. The idea that plants have feelings has caused many to believe that plants are sentient and capable of making deliberate choices. (We’ve discussed plant sentience in previous posts that you can see here, here, here, and here.)
Tree sentience! Artistic rendition thanks to Sylvia Thompson-Hacker.
I could spend my time debunking all the books, websites, and social media accounts that promote the pseudoscientific side of companion planting. But this popularized version is a horticultural zombie: it never dies. Instead, I’d rather discuss the ways that plants can change their environment physically, chemically, and biologically – which can influence the survival of other plants. The table below summarizes these methods.
I encourage you to download and read my recently published Extension manual – it’s free and peer-reviewed. In addition to providing solid scientific advice, it will help you understand why the classic example of companion planting – The Three Sisters – may be of historic and cultural interest but is unlikely to benefit plant productivity or soil quality.
Three Sisters Garden next to the Harry and Jeannette Ayer House, Onamia, Minnesota. Photo courtesy of Wikimedia.
Below are some evidence-based companion planting strategies for your gardens and landscapes. More are also available in the Extension manual linked above.
Perennial companion plants will take a year or two to establish. Annual companion plants should be used if immediate benefits are desired.
If you are growing perennial crops, avoid using annual companion plants that require yearly soil disruption. Crop growth and yield can be negatively affected.
Use living mulches on pathways, between rows in vegetable gardens and orchards, and other locations that are not densely planted to reduce competition. Living mulches play a crucial role in protecting soil from erosion as well as biological and chemical degradation, and this improvement may outweigh any drawbacks from competition.
To reduce competition among desirable plants, choose species whose roots are less likely to interfere with one another. Intersperse large taproot vegetables like carrots and radishes with those whose root systems are shallow and widespread, like corn, onions, and lettuces.
Avoid invasive species and aggressive native plants. They will be overly competitive for resources like sunlight, resulting in reduced growth and vigor of other species.
A well-chosen organic mulch will improve plant growth and productivity. A woody organic mulch, such as arborist wood chips, will enhance mycorrhizal populations, improve overall soil health, and control weeds. Arborist wood chip mulches also house predatory spiders and insects, such as ground beetles.
In vegetable gardens, try to intercrop different species so that individuals of the same species are as far apart as possible from each other. This will reduce the ability of pest insects to infest an entire crop.
Intercropping coconut and Tagetes erecta (marigold) in Kerala, India. Photo courtesy of Ezhuttukari through Wikimedia.
Earthworms have held a secure place in the hearts of many gardeners for quite some time. Charles Darwin himself was endlessly fascinated by these organisms (publishing an entire book about them in 1881) writing: “it may be doubted whether there are any other animals which have played so important a part in the history of the world…”.
Recognized for their benefits to soils, including improvements in water infiltration, aeration, porosity, tilth, organic matter, beneficial microbes, and the list goes on, it is not difficult to see why. These positive impacts can be seen in home gardens and agricultural operations alike, with studies showing significant improvements in crop production correlated with the presence of earthworms. As such, terrestrial earthworms are often referred to as ‘ecosystem engineers’ due to their immense impact, and have been intentionally (and accidentally) introduced to previously worm-free areas. Many of these impacts and benefits are highlighted by Sjoerd Duiker and Richard Stehouwer’s earthworm article for Penn State Extension.
That being
said, we have also started to hear a lot more about “invasive earthworms”, “jumping
worms”, “stink worms”, – paired with statewide and regional campaigns
encouraging people to reduce human-caused introductions and spread of
non-native earthworm species in areas where they could cause significant harm
to natural ecosystems and major hassles for managed ecosystems as well.
With all kinds of variable information out there, I thought it would be fitting to elaborate on the topic of earthworms, with the hopes of educating myself (and fellow readers) on some of the history, science, and misconceptions on this pretty popular garden-related topic. Having personally worked in North American horticultural systems, much of this information will be tied to the trends that we observe here, however I will also share some resources at the end that will elaborate on earthworm trends outside of North America (for those interested in learning more about the topic).
Earthworm
Biology
Before we
get into the nitty gritty, let’s learn a bit more about earthworm biology. There
are thousands (an estimated 3000-7000) of earthworm species around the world,
and these can be found on every continent except Antarctica (because earthworms
cannot survive in permafrost or underneath glaciers). Most earthworm species
vary in size from 10 millimeters (0.39 inches) to over a foot (12-14 inches) in
length. There are even giant earthworms: such as the giant Oregon earthworm
that is 4.3 feet (1.3 meters in length), the Australian giant Gippsland
earthworms which can grow to 9.8 feet (~3 meters) in length, and the giant
African earthworm with the largest earthworm specimen ever recorded, measuring
up to a staggering 21 feet (6.7 meters) in length.
These
thousands of earthworm species can be divided into 3-main groups:
Compost and litter dwellers (Epigeic)
This group feeds on leaf/crop litter, and as such, can be found at the interface of litter and soil (around the soil surface). These earthworms are typically smaller in size than the other groups, do not consume large amounts of soil, are not as good at burrowing, and are also used in composting systems. Example: red wigglers (Eisenia fetida)
Topsoil dwellers (Endogeic)
Species in this group live within the top few inches of soil, subsisting on partially decomposed organic matter present within the soil. These earthworms create horizontal burrows, filling them with their excrement (after ingesting large quantities of soil). These species can be identified by their lack of skin pigmentation, appearing grey, blue, yellow, white or pink. Example: angle worms (Aporrectodea caliginosa)
Subsoil dwellers (Anecic)
This group can be found deep within the soil (up to 6 feet below the surface), living in permanent vertical burrows. They require plant residue on the soil surface in order to survive. They also ingest large quantities of soil, and deposit their excrement at the soil surface. Example: common nightcrawler (Lumbricus terrestris)
Earthworms
(Clitellata) are a class in the phylum of annelids (segmented worms). They can
be characterized by their clitellum (a reproductive band that secretes a fluid
to form a cocoon for their eggs). They have both male and female reproductive
organs, though they require another individual for mating (where their eggs are
fertilized by another’s sperm and vice versa). Depending on the species, they
can produce between 3 to 1000 cocoons (containing anywhere between 1 to 10
eggs) per year. A majority of this occurs in the spring or early summer.
Like many
organisms, environmental conditions and human management practices can have
significant impacts on their populations and activity. Moisture, temperature,
soil texture, pH, and availability of food are some of these environmental factors
that can have a considerable impact. Although excess moisture is not ideal,
earthworms can survive in high moisture conditions if oxygen availability in
the water is sufficient. In dry conditions, they can enter a temporary
hibernation stage (diapause), descend deeper into the soil, or even die (which
can reduce earthworm populations in many areas during the summer months and in prolonged
periods of drought).
Management
practices such as reduction in tilling frequency, soil amendments (such as
compost and manure), crop rotation, surface plant/crop residue, and use of certain
fertilizers and lime are often linked to favorable impacts on earthworm populations.
Whereas increased tillage, soil acidification, removal of surface crop/plant
residue, and the use of toxic products such as certain pesticides are associated
with a negative impact on earthworm populations and activity. (You can learn
more about these in the Penn
State Extension earthworm article).
History
of Earthworms in North America
There are
approximately 300 species of earthworms native to North America, and these are
primarily found in previously unglaciated areas (such as the Pacific Northwest,
South-Eastern U.S., Mexico, Central America, and the Caribbean). In the rest of
the continent, most of our earthworm species were wiped out during the last ice
age either through direct glacial cover or frozen ground (even if it was quite
a distance away from the glaciers).
Since European colonization of North America several hundred years ago, earthworms of European origin were introduced and have now become widespread in many areas, including those that had been previously worm-free since the end of the last ice age (such as the mid-western and northeastern U.S.). According to a 2024 study by Mathieu et al., at least 70 non-native earthworm species have colonized North America, which measures up to be 23% of the continents known earthworm species. Many of the most ‘familiar’ and commonly seen earthworm species that you may have in your landscapes may be introduced earthworms like the infamous nightcrawlers (Lumbricus terrestris), often referred to as common earthworms, which are actually European natives. These, along with around several other very competitive earthworm species have become globally widespread and some of them are even considered invasive species in many regions.
You might
think, with the significant ecosystem services provided by these ecosystem
engineers, is the introduction of non-native earthworm species to previously
worm-free areas really that bad? The answer to this, is YES. Although
the impacts of many of these non-native earthworms have been considered positive
in agricultural (and home garden) situations, the impacts on natural ecosystems
can result in significant ecological impacts. Additionally, not very much
research has been conducted on long-term impacts of these organisms in
different ecosystems. Though these effects will vary by species and ecological
group, some earthworms have been associated with significant negative impacts to
ecosystem processes. This has included the reduction of understory litter,
impacted plant and fungal communities that are able to survive in these
landscapes, has been associated with an increase in soil erosion, and had
immeasurable impacts on many food webs. You can learn about the physical,
chemical, and ecosystem impacts in greater detail from
this publication by USDA’s Northern Forests Climate Hub.
Furthermore,
some of these larger and more competitive non-native earthworm species have the
potential to displace indigenous earthworm species which can often be more
sensitive to soil disturbance than their introduced counterparts. The establishment
of some of these non-native species around the globe can result in untold
impacts on native earthworm species worldwide.
This spread
followed by the immense ecosystem impacts that have and continue to occur have
been dubbed by some as “global worming”.
Common
Questions
Can (/should)
you introduce earthworms to your garden?
Whether you
have compacted soils, low organic matter, or any other reasons, you may be
tempted to consider trying to boost your local earthworm populations (in order
to reap all the benefits associated with them).
First of
all, you should never move around invasive species, nor introduce organisms that
you do not know very much about to a new landscape. Not only is it illegal in
many locations to intentionally introduce certain exotic species, it can also
be irresponsible. I think we all know and understand why this is a bad idea, so
I won’t go into too much detail.
Even if you
did become an expert in earthworm identification, and could differentiate
between native vs. non-native species (and know about the established
earthworms in your landscape), it still may not be a great idea to introduce
earthworms to a new location (especially if you reside in one of these
historically worm-free areas). We know that introductions and releases of
organisms to new sites can have a variety of negative consequences (even if
they may be indigenous to the area or already well-established) [many of these were
mentioned in my Blog
Post on Releasing Lady Beetles and Mantids for pest control in home gardens].
Even if you did manage to introduce them, they may not survive long-term nor stick around. That being said, good gardening practices may naturally attract earthworms to your gardens (without the need and potential negative impacts of introducing them yourself). So continue working on being an ecologically-responsible gardener, and enjoy the many benefits of this.
What
about earthworms in my compost?
Because of
earthworms’ ability to breakdown plant residues and convert them into valuable
soil amendments rich in organic matter, composting using earthworms
(vermicomposting) has become fairly widespread. These worm composting systems
rely on earthworms such as the European red wigglers (Eisenia fetida),
which are a common commercially available species. Although composting with
earthworms is a well-established tool for gardeners, it is important to be a
responsible vermicomposter to limit any unintended negative effects.
The contents of an indoor worm bin being assembled by gardeners at a workshop. Photo: Abi Saeed
In areas where you do not know very much about your local earthworms and the ones that you are using in your compost (especially if you are located in previously worm-free regions), keep your worm bins contained, and do not introduce worms and cocoons in your gardens (especially if you live in proximity to natural areas). Strategies to accomplish this include creating a screen to separate your finished compost from your worms, inspecting it thoroughly for worms and cocoons and/or freezing your compost before you use it in your gardens.
Should we
be working on managing these non-native earthworms?
As we know
from countless examples and extensive previous experience, it is nearly
impossible to eradicate established non-native (especially invasive) species.
Due to the fact that many of these non-native earthworm species are widespread
as a result of human transport, there is little that we can do to remove them
from landscapes in which they currently thrive (especially without doing
significant harm to other organisms that share those ecosystems). What we can
do, however, is to limit the introduction and spread of non-native
earthworm species through responsible gardening/farming (not moving around
compost with earthworms or their cocoons to new sites), and recreation
practices (avoiding the transport of leaves, mulch, and other plant debris into
natural areas, and disposing of fishing bait appropriately).
We have a guest writer for this week’s GP blog post, Teresa Watkins! She’s a professional landscaper and garden consultant in Florida (her bio is at the end of the column). As a professional she has seen “landscaper results” that will astound, scare, shock, or otherwise perturb you to no end. She has graciously shared photos and input for this blog post.
We hope this will be a series highlighting what to watch for when hiring a landscape company. Most of the following examples will have a “Caveat Emptor” feel to them. Just sayin’.
GP disclaimer: If you’re bothered by anything in this blog post please do not hold it against Ms. Watkins. Blame the editor who may have taken some liberties with the captions depending on how frustrated they felt at the time.
Let’s get started.
Case #1. Your landscaper charges you to edge dirt.
Don’t pay for “fluff work;” always inspect the bill and the job. Don’t assume the crew sent to do the job knows what to do. It’s up to you to know what needs to be done in your landscape. Please, always be polite when talking with the crews. They’re just doing their job.
Case #2. Your landscaper cut your plants so low to the ground they die.
Beware of landscaping crews wielding hedge shears and loppers, or even weed whackers. Yes, we’ve seen those used for a job like this. Make sure crews understand when to prune and how much to remove. This applies to cutting back or shearing shrubs into cupcakes, “Ding-dongs,” or other snack food shapes. Continuous shearing leads to early plant decline due to excess interior growth and shading. And it’s ugly. Actually, if you have shrubs or hedges that have to be continually cut back perhaps it’s time to rethink that particular part of your landscape.
Case #3. Your landscaper continues to commit crepe murder.
Case #4. Your landscaper plants a shade species in full sun, or vice versa.
OK, we can see what they were going for here – a color pop. But please read the plant tag!Always review the proposed plant list and diagram, and ask questions. Don’t trust the crew to know which plant goes where. They’re human and can make mistakes. If you’re concerned about what they’re doing tell them to stop and call the company owner or whomever you talked to and explain the situation. Remember you’re in charge, it’s your money, but always be polite. …And those ferns look crowded for their mature size.
Well, they did follow the work order.
Case #5. Your landscaper insists on using herbicides for weed control along lawns, gardens and fence lines.
These photos show the accumulated effects of herbicide. There’s a three month’s difference between the photos; please note the continued plant death. Be sure crews are state certified pesticide applicators or have training in the application thereof (requirements vary by region). As the homeowner it is your responsibility to know what’s being sprayed.If you don’t want herbicides used then it’s up to you to specify that. If your requests are being ignored then it’s time to change companies. If the crew starts spraying against your wishes tell them to stop immediately. But be polite – they’re just doing their job.
Oops.
Our guest blogger, Teresa Watkins, is a landscape designer and owner of Sustainable Horticultural Environments. She creates unique, beautiful, and sustainable landscapes with her “gardening with soul” philosophy. Over 40,000 homeowners and professional landscapers have attended Teresa’s talks and programs. Teresa hosts Florida’s most popular syndicated radio garden show “Better Lawns and Gardens” Saturday mornings on WFLA-Orlando, iHeart, Spotify, Audioboom, iTunes, and on podcast. She enjoys traveling and leading garden tours, checking off incredible national and world gardens on her ‘bucket’ (pronounced ‘bouquet’) list. www.she-consulting.com
In my blog post last month, I mentioned the likelihood of having a very active Atlantic tropical season, especially because the ocean surface temperatures are so warm. But despite an early start to the season with the first three named storms (including Beryl, the earliest ever category 5 storm in the Atlantic Ocean), it’s been quiet for the last few weeks. The ocean temperatures continue to be very warm. What is preventing the development of tropical storms in such a warm environment? One of the main culprits now is Saharan dust that blows west off the African continent and affects the vertical structure of the atmosphere. This keeps tropical waves from developing the necessary circulation to strengthen into a powerful storm. In this post, we will discuss the impacts of the Saharan dust and how it is both good and bad for the environment.
The Sahara Desert covers most of the northern portion of the African continent. It’s the world’s largest source of wind-blown dust supplied to the ocean and adjacent land. It is one of the driest places on earth and is covered with sand and rocks but very little plant materials. This means the dust from the Sahara is mineral dust with low organic content. Seven elements (Ca, Mg, Al, Ti, Fe, K, and Na) account for 98% of the total analyzed inorganic burden. The dust particles are often very fine, so they can travel a long distance from their source region on the continent.
Sand blowing on dunes, muffinn from Worcester, UK, Commons Wikimedia.
Winds in that part of the world blow from east to west near the surface. You might know of them as the “trade winds”, which are often described in elementary geography classes as the winds that helped European ships travel west to North America. The trade winds form a band of westward-blowing winds from about 30 degrees south to 30 degrees north latitude around the globe. The strength of the trade winds changes over time, but when they are strong and a lot of dust is available over the Sahara, the particles can blow all the way across the Atlantic, covering large parts of the Atlantic and bringing low air quality and beautiful sunrises and sunsets to people in its path. This month has been particularly dusty, with satellite records showing this is the 2nd dustiest July since continuous records began in 2002. Generally the dust plumes occur at a height of 5,000 to 20,000 feet where the trade winds are the strongest.
How does Saharan dust affect tropical storm development?
The air that carries the Saharan dust is usually very dry, which disrupts the usual moist conditions above the ocean surface and keeps thunderstorms from growing vertically. The vertical air movement would normally help initiate the decrease in surface pressure that helps storms grow. The dust particles also serve as nuclei to absorb even more moisture from the air, keeping the layer dry. The dust is opaque (which makes it visible from satellites) and shades the surface of the ocean, cooling it off and reducing its ability to energize storms.
June 18, 2020, NASA-NOAA’s Suomi NPP satellite, via Commons Wikimedia.
The Saharan dust layer is most likely to occur in the period between
mid-June and mid-August, but there are variations
over time and location because of the strength and direction of the wind.
Sometimes the winds even blow from south to north, bringing
dust to Europe, although this is less frequent. Tropical storms can
sometimes form in pockets of relatively dust-free air, as Hurricane Beryl did
this year, but the thickest layers are very effective at shutting down storm
growth.
How does the dust affect air quality and human health?
Saharan dust incursions into the Southeastern United States
can often been seen in air quality measurements taken in cities around the
region. Like any other dust particles or other aerosols like smoke from forest
fires, the
particles can trigger asthma, burning eyes, and other symptoms associated with
bad air quality. The dust can be seen in lower visibility around the
cities, deposits on horizontal surfaces like cars and plants either directly
from the dust or from “dirty
rain” which contains the dust and brings it down to the ground. It can also
result in spectacular sunrises and sunsets due to the scattering of the sun’s
rays by the particles (similar to those from volcanic eruptions). If you are
sensitive to poor air quality and plan to work outside in your garden, you will
want to monitor air quality carefully and avoid the times when the pollution is
worst.
The moment of sunset, El Manara gardens, محمد بوعلام عصامي, MD. Boualam, Commons Wikimedia.
How can gardeners prepare for episodes of Saharan dust?
First, we need to recognize that while we have not studied Saharan dust impacts for long, it has been around for many years and is a natural part of the earth-atmosphere system. It has beneficial impacts on soil nutrients in tropical rainforests and gardens in the affected areas and helps reduce activity in the tropics early in the season. But with dust events decreasing in the next few weeks, we can expect the Atlantic tropics to start heating up again as the most active part of the season gets underway. Gardeners should monitor their plants for dusty conditions and should also keep track of air quality impacts if they have asthma or other breathing disorders that could be affected by the dusty conditions. Gardeners in other parts of the world should also be aware of sources of dust and other pollutants that could affect their gardens and their own health. The Garden Professors blog has discussed the impacts of dust on gardens in several of our previous posts so please search for them if you want more information.
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.
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.
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.
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.”
Does Epsom salt cure blossom end rot? Nope!
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.
Does gypsum cure blossom end rot? Nope!
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.
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.
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.
