The Garden Professors™

For those of us in the Southeastern United States, this past week has been a whirlwind of preparation for Hurricane Helene, followed by the terrifying storm itself and now, for some people, months of clean-up and houses, yards, and gardens that may never be the same. My post this week (I did not get to it last week because of the impending storm) will be about how to prepare for an extreme weather event, including where to find accurate and timely information on weather forecasts and how to prepare your house and garden for the extreme weather you may suffer. While we just went through a hurricane, this could apply equally to an ice storm or blizzard, derecho, tornado, or any rapidly occurring weather event. No matter where you live, you will experience extreme weather at some point and need to be ready for it. My post from last month, https://gardenprofessors.com/how-would-your-garden-handle-a-12-inch-rainfall/, was surprisingly prescient, since Helene also brought extreme rainfall to the Southeast, particularly to western North Carolina and Virginia and to the area around Atlanta, GA. Our hearts go out to all of the people affected by Helene and other serious weather disasters.

Preparing your property and garden for damaging wind and rain conditions

The best way to deal with an extreme weather event is to prepare for it well ahead of time. I used to play a game with my son when he was young: “Name all the ways that something could go wrong (in his case, what could make a train or airplane crash).” It is a surprisingly effective way to make you think about possible dangers that might lurk around your home if a severe weather event occurs and what you might have to do to minimize them. If you can identify the risks of an event, then you can address them before the roof starts to blow off and the trees start falling.

The first step is to look around the outside of your house for any potential threats to your property that could become safety issues in strong winds or heavy rains. If you have trees, are they healthy? Are there any low-lying or diseased branches that could come loose in a strong wind and hit your house or car? Could a 50-mph wind from the southwest (or whatever direction your storms usually come from) blow them into your windows or onto your roof? Are there any areas on the outside of your house that are in poor repair and in danger of failing in a storm such as a loose railing or fence? If you like decorative items in your garden like garden gnomes or shiny balls, can you remove them before a storm approaches so that they don’t become wind-borne missiles? You should also consider potential areas where erosion might be enhanced by the ground cover or slope and determine if there are ways to slow the flow of water to preserve your soil and garden design.

Once you identify potential problems in your yard, you can repair them before a storm comes. But you should also make sure that you have adequate insurance coverage and that you document what you have before a storm hits with an inventory or video recording. You might also need special insurance to cover extreme events; I read today that less than 1% of all residents of western North Carolina had flood insurance, even though many of them live in flood-prone areas. Floods are not covered by most homeowners insurance policies. Of course, there could be many reasons for not buying it, including high costs, but if an extreme event occurs, you are going to wish you had it.

Identifying location concerns that could affect your safety

No matter where you live, there are bound to be risks due to the location of your property. If you live on top of a hill, you are prone to experience more lightning and higher winds and potentially more snow since the temperatures at higher elevations are generally lower. If you live in a river valley, your property and gardens would be more vulnerable to floods but also to freezes since cold air drains downslope to low-lying areas. When you decide where to live, consider the land the house and garden are on and also how you get there, whether you have to cross rivers or go through areas that are heavily wooded, which could be a problem in high winds but also potentially in a wildfire. Where you get your water could also be a concern if your well has an electric pump and power is likely to go out.

Get ready to go or stay

Preparing for an extreme event means planning for providing food, shelter, and water for your family and pets if you plan to stay and planning for an evacuation if it is not safe to stay. There is a lot of information out there about this planning process and I am not going to list everything here but you will find some links at the end of this blog that you may find helpful. As I write this almost a week after Helene came through the Southeast, there are many people here whose power is still out and who may not be able to travel because of all the trees and power lines that are down in their neighborhood and who have no access to clean water because the water plants were destroyed or the electric pumps on their wells no longer work. It usually takes about 72 hours for outside help to start getting supplies into affected areas, so you need to plan for several days and perhaps much longer to provide everything you need. Eventually, help will come from a variety of federal, state, and local agencies and non-profits but often the first help comes from a neighbor with a chain saw or extra water. If you evacuate, you will need a plan to get out safely, including more than one possible evacuation route, plenty of gas for your car, copies of important documents, and a place to go, which may include housing for pets or livestock.

Getting the weather information you need to make good decisions

Once you have your plan for severe weather, you need to monitor the situation for potentially threatening situations. A smartphone weather app is an easy way to get your daily weather for regular planning purposes but is not adequate for situations when weather might be changing rapidly since the apps are often updated only once or twice a day. In severe weather, an old forecast is a bad forecast because things may be quickly changing and you need the latest information.

There are a number of apps and websites that you can use to monitor extreme weather events, including the National Weather Service local forecasts for frequently updated information, watches for potential severe weather, and warnings for when it is spotted. The National Hurricane Center is the official source of hurricane and tropical storm warnings and their maps are updated every three hours when a storm is present. Beware apocalyptic posts on social media that often show a single worst-case model run that has practically no chance of occurrence just to gain attention and clicks. Stick to expert guidance from trusted sources. You can also get information on what local conditions you might experience and the timing of wind and rain using the hourly weather forecast from the National Weather Service, although in a rapidly changing extreme weather event even these may not change quick enough to capture the evolution of the storm. Weather radios and some smartphone apps that are designed can provide information about watches and warnings based on your location. If you live in an area that is prone to flooding or severe weather or is in a floodplain or near the coast of the ocean, then you should pay careful attention to rain in the area upstream of you are or the likely storm surge from a tropical cyclone. Be prepared to evacuate if emergency managers ask you to.

Planning ahead can save lives

Extreme weather is something that we all need to plan for but that planning often falls by the wayside because of other pressing tasks. But if you can take the time to do some simple advance planning and be prepared to act when the event starts, you can save yourself a lot of work later on when the clean-up begins and may save your houses and gardens. You may even save your family from serious consequences! I hope that it never becomes an issue for you, but I also know that many communities, businesses, farms, and families are dealing with the consequences of extreme weather now. Thanks to help from many people, they are starting to rebuild their lives, but it will be a long time before things get back to normal and for some, it may never be the same.

Some useful links:

Georgia Department of Public Health: Severe Weather Preparedness

Resident’s Handbook to Prepare for Natural Hazards in Georgia (good for other locations too)

Bankrate: How to Create a Home Inventory

FEMA: Hurricane Preparedness and Evacuation Planning

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.

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.

S = scam. Scammy sources of information exist to sell stuff. Websites selling seeds for nonexistent flowers whose pictures are generated by AI are scammy.

U = useless. Useless information promotes something that has no effect. Adding eggshells to gardens for any purpose is useless.

R = ridiculous. Ridiculous recommendations defy even common sense. Placing plastic forks into the soil to discourage animals from digging is ridiculous.

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!

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.

What happens as the rain is falling?

Tropical rainfall (or rain from any heavy thunderstorm) contains a large volume of water in droplets falling from a height of several miles. Generally, the raindrops are large and fall in a shape that looks more like a hamburger than the typical teardrop we often see in pictures. As the drop falls, the bottom flattens out under the influence of the air that it is falling through and surface tension holds the drop in a rounded shape. Raindrops fall at different speeds depending on how big they are. Large raindrops associated with warm weather and strong updrafts like the ones we see in thunderstorms and hurricanes can have a falling speed of up to 20 miles per hour, while smaller raindrops fall at lower speeds of 2 miles per hour and drizzle at much slower speeds of a few feet per second. The speed at which the drop falls is known as its terminal velocity and is reached when the force of gravity pulling the drop downward matches the friction of air slowing the drop down as it falls.

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.

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.

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!

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.)

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.

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.

…Or “When to Fire Your Landscaper”

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.

Case #2. Your landscaper cut your plants so low to the ground they die.

Case #3. Your landscaper continues to commit crepe murder.

Case #4. Your landscaper plants a shade species in full sun, or vice versa.

Case #5. Your landscaper insists on using herbicides for weed control along lawns, gardens and fence lines.

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.

What is Saharan dust and where does it go?

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.

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 2^nd 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.

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.

How does the dust affect plants?

Saharan dust has important positive impacts on both phytoplankton in the ocean and on the Amazon rainforest. Those areas are often missing nutrients that would allow plant growth and so additions of iron and phosphorus into those areas can improve soil or water fertility and plant growth. Unfortunately the dust can also contain bacteria or other organic material that can lead to undesirable growth of algae in the ocean. The dust is not acidic, so acid rain is not something we worry about with rain containing the Saharan dust, unlike rain from volcanoes or from coal-burning power plants. The dust can also reduce absorption of sunlight by plants if there is a large amount.

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.

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.

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.

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.

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.

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.

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.

Where do tropical storms and hurricanes form?

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

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.

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.

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.

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

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

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

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

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.

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

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

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

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

Stay tuned for next month!