The Garden Professors™

I thought this would be a fairly straightforward individual to research and write about. But no, talk about a rabbit hole.
Have you ever known someone that makes you ask, “They did what?” or “They’re where?” or “What are they up to now?”
If so, then you’ll recognize the type in this installment of People and Plants.

Friedrich/Frederick Adolph Wislizenus  was a German-born American medical doctor, explorer and botanist. The name Wislizenus traces its etymological roots back to Poland, specifically the town of Wislicza.
Friedrich A. Wislizenus is known for his printed recollections of travels to New Mexico territory and northern Mexico. He was born in Königsee, Germany on May 21, 1810, the youngest of three. The children were orphaned very young and a maternal uncle took them in. After completing “high school” at the Rudolstadt Gymnasium, Friedrich continued his studies at the Universities of Jena, Goettingen and Würzburg. In April 1833 he took a break from his schoolwork by actively participating in a revolutionary uprising against the existing German government. (Another participant of this event was Ferdinand Lindheimer.) The expected groundswell of support from the citizenry didn’t happen while a strong police presence did. In response Friedrich suddenly decided he should leave town.

He wound up in Zürich, Switzerland where he matriculated at the University of Zürich. His studies again suffered a brief interruption when he joined a movement to free Italy from monarchical rule. The expedition was disarmed by Swiss troops before reaching the border. There was nothing for our Friedrich to do but go back to the college from which he graduated in 1834 with high honors in Medicine.
Thereafter he decided to move to Paris to work but found no opportunities, so in the fall of 1834 he sailed for New York to hopefully establish himself in his profession.
By 1837 he had journeyed to Mascoutah, Illinois on the outskirts of St. Louis and was practicing his trade. Finding the practise of a country doctor’s life dull, monotonous, and lacking in remuneration, he relocated to St. Louis in 1839. 

Before settling down to resume his medical career Friedrich decided to make an extended journey into the farthest West. Scraping together his meager savings, he left the banks of the Mississippi in the spring of 1839 as a member of one of the annual expeditions of the Rocky Mountain Fur Company. His travels lead him into the far Northwest to the Wind River Mountains and then over the Rockies. Friedrich eventually reached Fort Hall on the Snake River, near the present site of Pocatello, Idaho, which at the time was the Southernmost trading post of the English who still held Oregon Territory in I839.
That’s a lot of ground to cover in six months.

From Ft. Hall he intended to cross the Sierra Nevadas and wander into California. But this dream was shattered for the lack of a competent guide. So he ventured back along the banks of the Arkansas River to the Missouri border. This voyage proved to be quite an adventure due to the inability of finding facilities, supplies, and the lack of equipment. He finally reached St. Louis in 1840. His record of this journey of almost six months duration was first printed in German in 1840. His son later translated it into English and published it along with a biographical sketch in I9I2. Its observations on the flora and fauna are quite detailed and the Linneaus binomial scientific designations are often included. Topography and geologic findings are also noted along with meteorological reports.

Friedrich resumed his medical practice and soon became involved in various civic activities. He was a regular attendant at the Western Academy of Natural Sciences where he found a kindred spirit in Dr. George Engelmann. The two were to become life long friends to the extent of taking care of the other’s patients when one of them was out of town.
In 1846, finding he could no longer ignore his “itchy feet,” he joined a merchant expedition to Santa Fe in New Mexico Territory. With a goal in mind and the necessary instruments in a horse-drawn wagon, he and an assistant intended to gather information concerning a part of the continent about which little was known.

Upon reaching Santa Fe the intrepid band found the headlines and town chatter were full of news of the Mexican-American War. Despite the situation the group determined to travel south, cross the border, and make it to the state of Chihuahua by September, which they did. Immediately upon reaching their destination the entire company was imprisoned. Not being a man to waste an opportunity, Friedrich put the several months in a secluded mountain village to good use. The enforced stay resulted in collection of notes, observations and sketches concerning the flora, fauna, topography, and weather of northern Mexico. Finally in the spring of 1847 the prisoners were freed by Colonel Alexander Doniphan. Friedrich accepted Colonel Doniphan’s offer of a temporary appointment as surgeon in the U. S. Army and continued with the soldiery to the mouth of the Rio Grande. He then returned to St. Louis via New Orleans before 1847 had ended.

Due to the efforts of Senator Thomas H. Benton, whom he’d become acquainted with, Wislizenus was summoned to Washington, D.C., and requested to publish his recollections, Memoir of a Tour to Northern Mexico in 1846 and 1847 by A. Wislizenus, M.D. This volume corrected many erroneous views of the western country and provided detailed descriptions (with maps and sketches) of the lands near the Rio Grande. The Senate ordered printing of 5,000 copies, which was a lot for the time, for distribution.

Among the trophies brought from his travels were many new plants, both as samples and sketches. These were later studied by his good friend and colleague Dr. George Engelmann who named many of the specimens after Wislizenus.
Dr. Wislizenus also has a lizard named after him. The animal was first documented by Friedrich in Santa Fe, New Mexico Territory.

The next several years saw Friedrich getting married, becoming a father and traveling the world, including Turkey, a visit to his hometown, Panama and finally getting to visit the West Coast of America. He returned to St. Louis in 1852 and spent the rest of his life there. He pursued scientific and civic interests, being one of the founders of the St. Louis Academy of Science and the Missouri Historical Society. He continued to indulge his love of meteorology and botany as long as his failing eyesight would allow. He died in September 1889 and he and his wife are buried on their estate near Kimmswick, Missouri on a high bluff overlooking the Mississippi River.

Dr. Wislizenus’ writings are available here:
https://www.biodiversitylibrary.org/creator/253456#/titles

To see list of plants attributed to Dr. Wislizenus go here:
https://tropicos.org/specimen/Search and type Wislizenus in the Senior Collector box and click on Search.

If you find yourself singing “How Dry I Am” these days, you might be under the influence of a large, stationary area of high atmospheric pressure. This past month, most of the eastern United States has been trapped in this pattern, with warm temperatures, clear skies, and no rain at all for most of the past month. In fact, many cities are on the verge of setting new records for low or no precipitation for the month of October, and some may even break records for the driest month ever. In this post, I will discuss what high pressure is, how it affects precipitation and health, and what impacts these may have on your gardens.

What is atmospheric pressure?

Pressure is a measure of the force of the atmosphere pushing down on the surface of the earth. This is caused by the weight of the air above that surface. As you go up in the atmosphere in an airplane or as you climb a mountain, the amount of air that is above you decreases and the pressure goes down. Pressure also changes horizontally as differences in the temperature around you cause variations in the density of the air, leading to areas of high pressure where the air is more dense and low pressure where it is less dense. Wind is just the movement of air in response to differences in pressure as the atmosphere tries to equalize pressure everywhere horizontally. In the vertical, the pressure gradient pulling air up is balanced by gravity pulling the air down. The wind at the surface is controlled not only by the variations in pressure at the surface but also by friction and the revolution of the earth around its axis, which diverts moving air to the right of the original movement in the Northern Hemisphere and to the left in the Southern Hemisphere (we call that the Coriolis force). Because of the combination of these forces, air tends to spiral into the center of the lowest pressure and spiral out of the center of the highest pressure.

How does atmospheric pressure relate to precipitation?

As the air moves into the center of low pressure, it meets in the middle and rises up, since it cannot go down into the earth. Rising air cools off as the pressure decreases and eventually the water vapor in the air condenses and forms clouds and sometimes precipitation. In the middle of high pressure areas, the air sinks, leading to air that is heating up and evaporating any clouds that might have formed elsewhere. Skies may be bright blue due to the lack of water vapor in the descending air. A complete circulation is formed when air at the surface of the high moves out away from the center towards areas of low pressure, then rises up and spreads out away from the surface low, moving into the top of the high pressure column and sinking towards the surface. You can see this schematically in the diagram below.

When an area of high pressure persists over an area for a long time, the sinking air leads to persistent sunny skies and low humidity, making it very difficult for clouds and rain to form. In summer, these long-lasting high pressure centers can lead to heat domes and oppressive and dangerous conditions such as occurred in the Pacific Northwest a few years ago. In the winter, high pressure is often associated with cold outbreaks of frigid, dry and dense air moving south from the Arctic (in the Northern Hemisphere). Those conditions lead to freezes caused by temperatures that fall to 32 F (0 C) or lower due to low winds and no clouds to trap the heat near the surface.

This fall has been a textbook case of a strong high pressure that has parked over the eastern half of the United States, causing day after day of warm and sunny weather and almost no rain at all. I often think that a drought is just too many days in a row of nice weather (assuming you prefer sunshine, which not everyone does). Fall is the time of year when we tend to have the longest periods of dry weather in the Southeast, but the dry spell does not usually last as long as it has done this year. If you enjoy warm and quiet weather (or sometimes cooler and less humid weather if some dry air has moved in from the north), fall is the time for you to really enjoy your garden before it shuts down for the winter. The dry conditions are good for many farmers too, because the harvest of commodity crops like cotton are easier when the plants dry up. Grape growers also appreciate the dry conditions because it concentrates the sugar in the grapes, leading to more tasty wines. Large-scale areas of high pressure around 30 degrees North and South latitudes are related to the formation of deserts like the Sahara and the Desert Southwest in the United States because the sinking air prevents the occurrence of precipitation, although it can rain there too when the monsoon blows moist air into the region and heat makes it rise to form clouds and rain.

How does high pressure relate to health?

Air pressure variations can lead to health issues in some people. Most people seem to be affected by low pressure, which can cause sinuses and ears to hurt and bother some people’s joints. Changes from high to low pressure associated with the movement of cold fronts also bother many people with arthritis and can cause headaches in some sensitive people. In high pressure areas, most people feel more alive and active. It is hard to know how much of that is due to the pressure and how much is due to the persistent sunshine and lack of rain, though. Interestingly, there is some evidence that more women give birth when the air pressure is low, especially when there is a big change due to an incoming tropical cyclone.

Sinuses, inversions and trapping of aerosols

Air quality also suffers under high pressure because the sinking air traps pollutants near the surface of the earth. This can include soot, smog, and even pollen. The temperature of the air above the surface often rises with height before cooling off as you go higher in the atmosphere. We call this an inversion because we normally expect temperature to decrease as you rise away from the earth, and instead it rises over a layer near the ground before cooling off above that layer. Farmers spraying some herbicides are not allowed to spray when there is an inversion because it can lead to concentration of the chemical near the ground and drift into neighbors’ fields, causing damage to the plants there. This can also happen in home gardens if you have a neighbor that uses a lot of chemical sprays in his or her yard. In the worst cases, a strong and persistent inversion can lead to dangerous levels of pollutants that can cause harm to people with lung conditions like asthma. Smoke from wildfires can also get trapped under the inversion, adding to the pollutant load.

How you can plan for high pressure impacts

If you know that high pressure is forecast for your area, you can use that information to plan for the kind of weather you are likely to experience while it is in place. If it persists over the area, it will be dry and you may have to increase your watering. Plants may get dustier and could be affected by trapped pollution and chemical treatments, leading to spotting or discoloration of the plants and eventually death as the pollutants affect the soil. If you need to work outdoors during persistent high pressure, make sure you monitor the air quality levels so you do not irritate your lungs or dry them out in the low humidity of the sinking air.

Enjoy the days of high pressure as you work in your gardens in the sunny conditions. Low pressure will soon come and bring rain and clouds. We need both to keep our gardens and our gardeners happy!

While the onset of autumnal leaf color change reminds us that winter is coming, there are many other reasons why leaves turn red. Knowing why and how leaves turn red is key in accurate diagnosis.

These are examples of leaf reddening misdiagnosed as phosphorus deficiency:

These leaves are not phosphorus deficient, either.

Congratulations to accurate diagnosticians at UCANR! This is indeed phophate deficiency. Damage is not localized as in the previous images.

Here are some other underlying causes behind leaf reddening.

If you’re interested in learning more about how and why leaves turn read, be sure to download my most recent factsheet, appropriately titled “Why do leaves turn red?” ] It’s peer-reviewed and relevant to any part of the world.

Enjoy this Halloween treat!

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.