The movie “Field of Dreams” is a family favorite – we love how baseball and the supernatural are interwoven to create a great story. If you haven’t seen the movie, you should – and for those of you that have, you know why it was important for Ray to build the baseball field. Like the magic that unfolded once that physical space was provided, botanical magic emerges from garden soils that support mycorrhizal life. Garden product peddlers have taken advantage of the scientifically-established relationship between plants and mycorrhizal fungi by selling inoculants. And gardeners tend to focus on which of the many brands of inoculants to buy, rather on questioning their efficacy.
Choices, choices, choices
I’ve attached a link to my peer-reviewed fact sheet on mycorrhizae for a more in-depth discussion about this symbiotic relationship, but the bottom line is this: inoculants don’t work. To understand why, we need to consider a modified version of the disease triangle. Many gardeners are familiar with this concept, which depicts the three criteria needed for plant disease to manifest: the presence of the pathogen, the presence of a host plant, and environmental conditions conducive to pathogen growth. Pathogen spores are EVERYWHERE in landscape and garden soils – they just aren’t activated unless their host is present and environmental conditions allow their germination. Likewise, mycorrhizal spores are EVERYWHERE in landscape and garden soils. We can make a mycorrhizal triangle to visualize the three criteria for needed for mycorrhizae to develop.
Comparison between a disease triangle and a mycorrhizae triangle
While our understanding of mycorrhizal relationships continues
to expand, we do know some of the environmental factors needed for successful
inoculation:
Soil oxygen. Mycorrhizal fungi are aerobes,
meaning they are active when sufficient oxygen is present.
Woody debris on the soil surface. Mycorrhizal
species are also decomposers of woody material. There is increasing evidence
that a natural woody mulch (not sawdust, not bark) is required for mycorrhizal
establishment. Fungal hyphae colonize the debris, extract nutrients, and
transport them to their host’s roots. Arborist wood chips are an ideal mulch in
this regard as they absorb water and provide an ideal substrate for hyphal
development.
There is a robust body of peer-reviewed research conclusively demonstrating that commercial inoculants applied to plants in landscaped soils have no substantial effect on the development of mycorrhizae. This lack of efficacy has induced some inoculant manufacturers to add fertilizer, especially nitrogen, to increase plant growth and fool consumers into thinking the inoculant was responsible.
The image on the left is the label from a mycorrhizal inoculant. Close inspection (middle image) reveals addition of a fertilizer, which is identical in NPK content to a fish fertilizer (right image).
And here is the lesson “Field of Dreams” provides: if you build it, they will come. Build a healthy soil by mulching with a thick layer of arborist wood chips. Not only do they provide nutrients and absorb water, but their presence reduces soil compaction and increases aeration. You can be assured your plants will be successfully inoculated with your soil’s native mycorrhizal species.
This Quercus garryana seedling is already inoculated with native mycorrhizal fungi
There’s all kinds of maladies that can strike your garden plants throughout the season- diseases, insects, negligence, and more. But one common issue we are seeing more and more here in the corn belt and other places with lots of crop production is herbicide drift. Of course, you don’t have to have a corn or soy field nearby to have issues with drift – it can happen anywhere and anytime an herbicide is applied and proper precautions aren’t taken, even when you or a neighbor are just treating a small area in the yard. There are other avenues of herbicide damage on plants as well, such as using herbicide-treated grass clippings as mulch in the garden.
A wide variety of plants can be damaged by herbicide drift from a variety of different products – trees, shrubs, roses, vegetables, and more. The damage can be slight to severe, and unless the dose is large most plants will grow out of the damage. Vegetables and fruits, though, are of particular concern due to the potential food safety risk from residues of unknown herbicides on the plants. Therefore, it is especially important to be able to identify signs of herbicide drift and take the appropriate course of action which is usually and unfortunately removal of the plant from the garden.
I have to remove the plants!?!?
Yes, you read correctly, I said removal of the plant! I, along with many of my extension colleagues, encourage gardeners who have drift or herbicide damage on their plants to remove them from their gardens. Why take such a drastic measure, especially if the plant may actually recover and “grow out” of the damage? The answer is mainly one of safety. Since it is likely impossible to know exactly which chemical or product formulation was used there’s no way of knowing if the product is safe to use on consumable crops, whether its residue is safe, or whether it is systemic and has a residual effect. A gardener cannot know if there is a pre-harvest interval where the crop will be safe after a certain passage of time or if it will never be safe. And even if you do know the product (let’s say you were the one that used it or you know what is being used by the neighbors) it is likely that there won’t be safety information for use on fruit and vegetable crops, since we don’t typically apply herbicides to plants we want to keep growing. You should also remember that application of such herbicides to fruit and vegetable crops, even if accidental, technically constitutes an off-label (and illegal) application of an herbicide to a non-target crop or pest.
What are the most likely fruit and vegetable plants to be
damaged from herbicide drift?
While just about any plant can be damaged by herbicide drift if enough herbicide gets on the plant, there are a few plants that seem to be more susceptible to herbicide drift. This means that these plants exhibit damage with smaller doses of herbicides than others and will show damage while other plants nearby remain unfazed. The plant that we get the most calls about are tomatoes. This is the vegetable garden crop that is the most susceptible to herbicide drift and just so happens to be the most widely planted crop in the garden. The other edible crop that seems to be highly susceptible to herbicide drift is grape. While grapes aren’t nearly as common as tomatoes in home gardens, wineries in regions with high herbicide use rates are struggling to keep their vineyards going due to the damage.
I live nowhere near a big farm, how do I keep getting drift
damage?
Of course, drift can come from anywhere, even a small application of herbicide on a neighborhood lawn or garden. But under the right weather conditions (high temps and wind) some herbicides like dicamba can volatilize and drift for 2-3 miles or more. Even if you think you live nowhere near a farm or other area where herbicides might be used you can get drift from miles away. This makes it hard to pinpoint where the damage is coming from in order to sleuth out what exactly was used. This is especially tricky here in our area where the city of Omaha is surrounded on all sides by farmland, and even has pockets of productions fields sandwiched between residential areas. Unfortunately, one of the prime herbicide application times in our region is shortly after most gardeners plant their tomatoes so we get lots of calls and questions that end up being drift. Thankfully there’s usually still time to replant tomatoes, but it isn’t fun telling people that started plants of their favorite or special varieties that they’ll have to rip them out and go buy new plants.
The kicker is that drift can be random. It can be one or two plants out of a bed of
twenty, or one plant on one side of the garden and another somewhere else, or
an entire field full of plants. It just
really depends on the wind patterns and concentration of herbicide.
Is it drift? Or is
it something else?
At first glance it can be hard to tell if an issue is drift or something else since the signs can look like some other problem until you get up close. There are a wide variety of herbicides on the market and therefore there can be lots of different signs. The most common types of damage you’ll see are light/white colored and necrotic spots from exposure to broad-spectrum herbicides like glyphosate, and curling, twisting, stunting, yellowing, and epinasty from broadleaf herbicides like 2,4-D and dicamba. Epinasty is an unusual, twisting growth pattern on the leaves that result when one layer of the leaf (usually the upper layer) grows faster than the other. You can get weird strappy looking leaves, weird margins, and other irregular growth patterns. The damage from broadleaf herbicides can sometimes be mistaken for heat or drought damage, viral diseases, or even excess watering, all of which cause leaf curling of some sort. I’ll share a few tomato pictures below to demonstrate herbicide damage vs other types of leaf curling. For a great pictorial guide to herbicide damage symptoms, check out this resource form the University of Tennessee.
Symptoms of broadleaf herbicide (such as dicamba or 2,4-D) drift damage on tomato. Notice the irregular margins, strappy appearance, and curling of the leaves. The damage is usually limited to a small area on the plant. Photo: Patty Leslie
Note the irregular growth patterns of the leaves in this sample. Herbicide damaged leaves cannot be flattened out to look normal. Photo: John PorterWidespread damage, likely from application of herbicide-treated grass clippings as mulch. Photo: John PorterLeaf curling likely from excessive heat, NOT herbicide damage. Note that the leaves could be flattened to look normal. Photo: Scott Evans
Can you avoid drift?
Unfortunately, you can only control drift from the herbicides you apply yourself. Pesticides such as herbicides can be used safely and effectively if used appropriately. Reading and following the label instruction is important and is the law, paying special attention to wind speed, temperature, and application equipment, e.g., how fine of a mist does the nozzle create. Drift from the neighbors’ lawn treatment or a nearby farm is really outside of your control, so being watchful for signs of drift is important. Sheltering susceptible crops, like tomatoes, using something as a windbreak might be helpful. As this journal article points out, a windbreak or vegetative buffer around wetlands offers some protection and I noticed a similar effect recently in one of our Master Gardener project gardens. Our Master Gardeners grow thousands of pounds of produce a year for local food banks, and on a recent visit I noticed that about 25 percent of their tomato plants were showing signs of drift (and they were removed and replaced). The pattern was interesting – the only plants damaged were the ones on the outside edge of the garden and the ones along wide walkways in the garden. But plants in the interior were spared. So perhaps planting less susceptible crops on the exterior of the garden and along walkways to act as buffers might work.
And while it isn’t useful for home gardeners, specialty crop
producers (like those all-important wineries) and beekeepers can register for a
program called DriftWatch where they can
be informed when spraying will take place on local farms.
The word “sustainable” gained new life over the last few decades as the concepts of sustainable agriculture and now sustainable landscapes were developed. But what actually are “sustainable” landscapes? This is not something that is easily defined, so I offer my own ideas on the subject here. We can think about this and be thoughtful about landscapes and garden choices as we grow, plant, and maintain landscapes at home and in public spaces.
While this landscape has some of the elements of a sustainable landscape, it is very ugly, with tired artificial turfgrass. The first element of a sustainable landscape is that has an appropriate level of quality.
A sustainable landscape provides benefits
If we start with soil, and nothing growing in it, we can move forward adding landscape elements and benefits begin to emerge. Plants provide habitat for animals including arthropods. As the diversity of plants in a landscape increases, so does the diversity of visitors that use that vegetation. The sculpting of the land may create water catchment areas that help sustain soil moisture. Hardscape (walls, patios, water features and rocks) may create visual focus points. Plants provide many benefits such as sound absorption, dust collection, shade, food, and of course can also be aesthetic. The most sustainable landscape provides its benefits with a minimum input of water, fertilizer and labor to maintain.
While this landscape is visually appealing with specimen trees and broad swards of turfgrass it is not sustainable. The amount of water required to grow poorly adapted trees (some of which are now diseased) in this California climate and the energy required to maintain (mow turf) will require significant on going investments of time or money and hydrocarbons to fertilize and maintain it. Typical of many older landscapes there are no mulch zones.
A sustainable landscape is appealing
Why expend energy or
spend money maintaining an ugly landscape? Landscapes in order to be
sustained, must appeal in some way to those that use them. In some
cases plants in landscapes are adapted to their environment and
require little applied water, pruning or other maintenance in order
to survive and provide benefits.
Sometimes addition
of color to a landscape will help its visual appeal. Surveys of
gardeners suggest that colorful landscape are more appealing than
those that are only green in color.
Points of interest within a landscape make it appealing. Also, hiding the landscape with gates, shrubs or walls provides intrigue and beckons you forward to explore the unseen parts. While mass plantings of the same plant material can be stunning so can specimen trees or other plants that are strategically placed for high impact. Landscape art either man made or nature made (rocks and logs) can be become the focus of a landscape making it appealing.
In surveys of Master Gardeners this landscape is consistently rated higher than others because of its use of: color, specimen plants, attractive hardscape, presence of trees, and walls that provide some intrigue. The landscape is also easy to maintain and has a low hydrocarbon footprint
A sustainable landscape often contains trees
Trees are the workhorse of landscapes. They provide shade and thus reduce energy costs in landscapes and they are extremely visually aesthetic. Trees are very important for birds, insects, squirrels, and other animals. Trees remove carbon from the atmosphere and feed the soil food web with the captured carbon. Trees help increase the capture of rainfall and the water infiltration rate of soils. While trees do require maintenance (which can be expensive), maintenance costs can be reduced by proper selection, pruning and placement in the landscape. Trees also have proven health both (physical and psychological) benefits for people who live or reside near them.
Keukenhoff gardens in the Netherlands is world famous and has millions of visitors while it is open each year. Keukenhoff is sustainable because of the millions of visitors and sponsors that pay for its maintenance, the plentiful rainfall in the Netherlands, and the Benefits that it provides millions of people If we remove the trees from Keukenhoff we still have the tulips, but the landscape loses much of its interest and charm.
A sustainable landscape should not consume excessive amounts of
energy
The traditional landscapes I grew up with included lawns in the front and rear of residences. This of course required frequent mowing, often with gasoline powered equipment. Shrubs were planted that required shearing with electric or gas powered hedge clippers. Since mulches were never much used, fertilizers (derived from petroleum) were used to push growth which was clipped and hauled (using petroleum to power the trucks) to a landfill. As you can imagine a lot of energy is utilized to maintain such landscaping. Much of the petroleum-based energy expenditure can be mitigated by using more mulch especially if it is produced on site, limiting the expanse of turfgrass to needed areas, and planting or utilizing adapted plant materials to the site and climate. Surround trees with tree chip based mulches, not turfgrass.
This traditional landscape requires excessive pruning of the tree and shrubs and mowing of the turfgrass. Some labor is mitigated by using stone mulch on the side of the yard. This landscape may be over-planted but use of mulch cuts down the necessity of mowing, prevents weeds, and provides a place to recycle yardwaste in the landscape
A sustainable landscape should be water efficient
For those of us in the west we continue to suffer multidecade droughts. Water use efficiency is necessary for our landscapes to be sustainable because water is expensive and limited. For those that have excess water landscapes need to manage the excess water well without suffering erosion or soil nutrient losses that compromise the landscaping.
Sustainable landscapes provide room for waste recycling
One problem with
landscapes that don’t use mulch is that there is no place to
recycle used plant clippings. If landscapes are fertilized and
irrigated to produce lush growth that is then disposed of with a
waste hauler, this is not sustainable. It is best if clippings can
be resused as mulch under shrubs or in other out of sight mulched
places.
Sustainable landscapes use adapted plants
Adapted plants are not necessarily native plants but plants that can live in the soils at the site with the amount of water that is available to them with a minimum of extra care, fertilizer, requirement of pruning or other inputs (pest management) to keep them looking good.
There are likely many other tenets of sustainable landscapes, but these are some of the key factors. The landscape should be adapted to the climate, provide huge benefits and require less maintenance and then it is, by all means and metrics, sustainable.
This landscape uses garden art, fences and a specimen plant (Dasylerionlongissimum) to achieve impact. In the springtime the Wisteria next to the residence adds color. The landscape makes efficient use of water and is adapted to survive with rainfall. Stone mulches help cover the soil.
Did it rain enough last night to water your garden? Have you started running the sprinklers and aren’t sure if they’re running enough? Perhaps you’re not sure that new drip system you installed is doing its job. Or maybe you just want to be more efficient and careful with your water use. How can you know moisture is getting deep enough into the soil to benefit your plants. Is there an easy way to find out?
Yes there is – a simple soil probe will do the trick.
A soil probe can be anything long and sturdy enough to penetrate the soil at least 12 inches (~30 cm.). Handmade soil probes, long screwdrivers, skewers, even the spit from an old rotisserie grill will all work.
A probe made of metal will work best and for safety it should have a handle of some sort. If there’s no handle you should wear sturdy gloves when using it. This set of 22″ screwdrivers was purchased at the local outlet of a national low cost tool franchise. It meets all the requirements and is inexpensive. Plus it’s a set so there’s one for you and one to share!
While you only need the probe to go 12″ into the soil it’s helpful if the probe itself is longer, if only for convenince. The probes are shown here with a yardstick for scale. (Yardstick = 36″=~91.5 cm.)
So you now have a soil probe, how do you use it to measure soil moisture depth? Easy-peasy. Insert the probe straight into the soil at the spot you want to test. You’ll need to use firm pressure but don’t force it into the soil. The probe will pass through moist soil but stop when it hits dry. And this is true for any soil type, sand, loam or clay. When the probe stops, grasp the probe right at the soil surface and pull it out. The part beyond your hand towards the probe tip shows you how deep the moisture is.
Note: if you have rocky or stony soil the probe may hit a rock and stop. Usually you can hear or feel that it hit a hard object. Just adjust the probe’s postion and try again.
For trees, large shrubs and deep rooted grasses the probe showing a 12″ moisture depth is adequate. For shallower rooted plants or annuals 4-6″ is enough. Monitoring soil moisture depth is an easy way to know if your landscape or garden is adequately watered. Water is a precious resource, let’s not waste it.
To estimate how much rain has fallen on your property, check out this site: https://water.usgs.gov/edu/activity-howmuchrain.html?fbclid=IwAR3SFjeaflrsXyCtZ_qdUUeltuK9qzYolmybq0wz5KNH2xP9KdJf1g_uckk
You may have read in the news earlier in May that NOAA has updated their “normals” for temperature and precipitation at stations around the country. In climatology, normals are the calculated averages over a specified time period. Usually, we use a 30-year period to capture what the average weather is like in a time period that is about the length of a generation, but now NOAA is also calculating normals based on other time periods like 15 years. Utility companies often use 10-year normals because electricity-generating technology and energy demand is changing so quickly that 30 years is considered too long.
Source: Marc Schloesser, Creative Commons
Why do they update the normals every 10 years?
Normals are updated every ten years, so the new period of 1991-2020 is replacing the older normal period of 1981-2010. They only do it every ten years because a lot of work goes into quality control of the data as well as adjusting for station moves, missing data, and changes in observation time. All of those events can introduce artificial “climate change” into the record, leading to averages that don’t really represent the current climate at the location of the station being described. Climatologists follow rigorous methods of making these corrections, and even scientists who are skeptical about their techniques by and large end up with nearly the same corrections if they follow scientifically and statistically accurate methods. NOAA has provided some FAQs that explain more about the process of creating the new normals if you are interested.
How are the normals changing?
Determining what a “normal” temperature is when the temperatures are relatively stable is easy, because you can use any long-term average to describe the expected temperature. But when the climate is not stable but is changing over time, what you think of as “normal” weather changes as cooler decades get replaced by warmer decades. For example, here is a graph of the annual average temperature for the Midwest with 30-year normals plotted on it for 1961-1990 (green), 1971-2000 (blue), 1981-2010 (violet), and 1991-2020 (yellow). Early in the record, the 30-year averages (not shown for the early time periods) did not change all that much from one decade to the next because there was no trend towards warmer conditions. But now, every new set of normals gets warmer. We are not living in the climate that our parents or grandparents grew up in! This Washington Postarticle by Bob Henson and Jason Samenow provide an excellent overview of all the changes that we are seeing and why those changes are occurring. We can expect the next set of normals to be even higher as the temperature continues to rise.
The annual average temperature is not changing by the same amount everywhere. The map below shows that even though most of the lower 48 states are getting warmer, the upper Great Plains got cooler when the latest normals were calculated. Western Texas and parts of New Mexico had the largest increases in temperature. NOAA also has these maps for select months.
Of course, it is not just the annual average temperature that is changing. The minimum temperatures are increasing at almost twice the rate that the maximum temperatures are rising. Most but not all monthly temperatures are rising at many stations. The precipitation is changing in northern and western high-elevation areas from snow to more rain. Most parts of the US are getting wetter, but the Southwest is getting drier. And the rain is coming in higher intensity bursts, with longer dry spells between precipitation events in many areas.
As temperature and precipitation change, other variables that are related to heat and moisture are also changing. The length of the growing season is increasing in most of the country, allowing gardeners to plant new varieties of heat-loving plants but stressing plants that prefer colder temperatures. This is a concern for peach farmers in Georgia, for example, since peach trees need a certain number of hours below 45 F to set a good crop of fruit. As the temperature rises, it becomes harder for the trees to get the cold weather they need to produce enough blooms. Other plants like lilac, which I enjoyed every spring when I was growing up in Michigan, do not grow in Georgia because of the heat and may someday be scarce even in the Midwest. Growing degree days (a measure of the amount of time above a base temperature, commonly 50 F, used to track plant development) are increasing, affecting the growth patterns of commercial crops as well as garden plants. Humidity is also rising, leading to more fungal diseases and more oppressive working conditions for gardeners and farm workers who are affected by both the higher moisture levels and more frequent extremely hot days. At the same time, higher evapotranspiration from plants accelerates the water cycle, making droughts (and floods) more likely.
Where do you find your local normal weather?
If you are interested in finding your new “normal”
temperature and precipitation and comparing it to the old values at your
location, you can find instructions at my daily blog.
Of course, there are many other places to find it as well—just do a search
online and several sites should pop up. If you want to do an average over a
different set of years, you can use the Custom Climatology Tool from the
University of Nebraska-Lincoln to do those calculations.
Ultimately, the changes in the climate reflected in the new
normals will show up in other garden-related values such as the USDA Plant
Hardiness Zone, although it’s hard to know exactly when those values will be
updated. Even without knowing exactly what zone you are likely to be in over
the next decade, with the continuation of rising temperatures that we expect,
you can try out plants that are just on the warm side of your current zone to
see how they do. Of course, your local microclimate will also affect their
ability to thrive, so don’t forget to consider that too.
Should we just get rid of “normals” since they keep
changing? I don’t think so, since they do provide useful information about what
we expect over a number of years. You can use normals to determine what clothes
to have in your closets, how much heating and cooling you need for your homes,
and what to plant in your garden. Just be aware– “normal” is no longer normal
in a changing climate.
A seedling with green cotyledons and emerging radical
Most of us have witnessed dicot seed germination at some point in our lives – watching the coytledons transform from seed halves to green, photosynthetic structures, while the radicle developed into the seedling root system. This seedling root – or taproot – is important to seedling survival as it buries itself in the soil to provide structural support and to give rise to fine roots for water and nutrient absorption. But that’s where much of our visual experience ends – because we don’t see what’s happening underground. Without additional visual information we imagine the taproot to continue growing deep into the soil. And while this perception is borne out when we pull up carrots, dandelions, and other plants without woody root systems, the fact is that woody plants do not have persistent taproots – they are strictly juvenile structures. Understanding the reality of woody root systems is critical in learning how to protect and encourage their growth and establishment.
Mature carrots have taproots. Mature trees do not. Photo courtesy of Pixnio.
Trees, shrubs, and other woody perennials all have juvenile taproots just like their herbaceous counterparts. But these long-lived plants develop different morphologies over time, which are primarily determined by their soil environment. Water, nutrients, and oxygen are all requirements for sustained root growth. Gardeners always remember the first two of these needs, but often forget the third. And it’s oxygen availability that often has the biggest effect on how deeply root systems can grow.
Roots grow where they can. Sometimes that zone can be very shallow, as this coastal forest photo shows.
Whole-plant physiologists have known for a long time that “roots grow where they can” (Plant Physiology, Salisbury and Ross, 1992). But this knowledge has become less shared over time, as whole-plant physiologists at universities have been largely replaced by those who focus on cellular, molecular, and genetic influences (and can bring in large grants to support their institution). Sadly, many of these researchers seem to have little understanding about how whole plants function. Simply looking at the current standard plant physiology textbook (Plant Physiology and Development, Taiz et al., 2014) reveals as much. (To be fair, there is now a stripped-down version of this text called Fundamentals of Plant Physiology, [Taiz et al., 2018] but even this text has little to do with whole plants in their natural environment.) If academics don’t understand how plants function in their environment, their students won’t learn either.
The Table of Contents for Plant Physiology and Development. You won’t find a discussion of woody root ecophysiology in here.
Well. Time to move on from my soapbox moment on the state of higher education.
Roots grow where oxygen is plentiful. It becomes a limiting factor as soil depth increases. Photo courtesy of Wikimedia.
Let’s look at what happens with a young tree as it develops. The taproot grows as deeply as it can, but eventually runs out of oxygen so vertical growth stops. At the same time, lateral root growth increases, because the levels of oxygen closer to the soil surface are higher. These lateral roots, and their associated fine roots, develop into the adult root system, continuing to grow outwards like spokes on a wheel. When pockets of oxygen are found, roots dive down to exploit resources. These are called sinker roots and they can help stabilize trees as well as contribute to water and nutrient uptake.
Gardeners and others who work with trees and other woody species would do well to remember that woody root systems, by and large, resemble pancakes rather than carrots. These pancakes can extend far beyond the diameter of the crown – so this means protecting the soils outside as well as inside the dripline.
Typical root structure of a mature tree in its natural environment. No taproot here!
Given the growing (haha) popularity of vegetable gardening over the last several years, which has gone into overdrive during the pandemic, more and more people are looking for innovative ways to grow in all kinds of spaces. Container vegetable gardening can be as simple as popping a tomato into a bucket, but there are lots of different ways to successfully grow crops in small, mobile containers. It is possible to grow full sized crops in containers, given a large enough container and space to grow. But more and more plant breeders have been developing small and dwarf cultivars of lots of different kinds of crop plants to meet the burgeoning interest in container and small space gardening. Let’s talk a bit about growing in containers, about some of those crops that do well in containers (including some dwarf/small cultivars, and even some design to make those vegetable containers attractive on your patio or porch.
Container Culture
Growing vegetables and fruits in containers follows the same general rules that ornamentals and houseplants follow. We’ve covered several container questions here on the GP blog, which you can find here. Probably one of the biggest questions (and myths) that we encounter is the placement of rocks or other items in the bottom of pots for drainage. It is a common question over on our social media. So to just get that out of the way, don’t do it – it actually makes drainage worse. The only exception might be if you are using a really large, deep pot and need to fill it with something so you don’t have to fill it all the way with soil – but you still need to ensure that the soil is sufficiently deep so that you don’t end up with waterlogged soil in the root zone.
Here are some other best practices to keep in mind:
Use only good quality potting mix, not garden soil, top soil, or “bargain” potting mix. Container culture means that soil needs to be “light and airy” to ensure proper balance of soil, air, and water.
Leafy greens can be grown in shallower pots than bigger crops like tomatoes and peppers.
Choose the right size and shape of container for the job. You have to look at container diameter for the plant size, but also ensure the proper depth and volume of soil to support root growth. Small crops like leafy greens can make do in a shallower container, but large rooted plants like tomatoes and peppers will require a larger volume. For example, you can grow one tomato plant in a five gallon container (if you’re a “thrifty” gardener, this means you can drill some holes in the bottom of a food-safe 5 gallon bucket). But you can also grow 12 carrots in the same size container, given that the soil is deep enough to accommodate the carrots. For a good size and spacing chart for “standard” sized crops, check out this table from UF Extension.
Drainage is a must. Make sure your containers have good drainage holes (and don’t add rocks!). If your containers are in an area exposed to rain, it would be best not to have saucers under them so that they don’t sit in water.
Make sure the containers are food safe. This isn’t an issue if your using just about any purchased container meant for container gardening, but if you’re repurposing containers you want to make sure they won’t breakdown or leach chemicals into the soil. Some plastics will break down in sunlight, but most should be food safe. The one big exception is plasticized (softened) PVC. Hard/rigid PVC is OK, but the softer plasticized versions can release dangerous phthalates when breaking down. You can look for the number 3 in the recycling symbol to know if you have PVC, and if it is soft and pliable don’t use it. Galvanized metal is another risk, as it can release zinc or cadmium into the soil both of which are harmful to humans. This is alarming as metal containers and raised-bed garden kits have been hitting the market and lots of people grow in galvanized livestock tanks. Be sure if you are using metal containers that they are either not galvanized or are sealed (or you create a barrier) if they are.
Make sure the light is right. Growing in containers doesn’t mean that tomatoes and cucumbers will become shade-loving plants. You’ll still need a minimum of 6 (preferably 8-10) hours of full sun for most fruit or root crops. You can grow shade tolerant crops, like most leafy greens, in shaded areas such as covered porches and under trees.
Nutrients are limited to what is in the potting soil, so keep an eye out for signs of nutrient deficiency and fertilize accordingly. Most potting soil comes with an initial dose of fertilizer, but you’ll probably need to add more through the season.
Keep on the lookout for insects and diseases – they still happen in container plants, too.
Little Plants for Big Flavor
It is possible to grow most standard vegetable plants in containers, save for maybe giant plants like pumpkins and some squashes. However, breeders have been developing numerous crops in small, container-ready sized plants over the last decade or so. These cultivars can let you grow more plants in smaller containers. For many, the fruit or harvestable portion is similar to that of the standard sized plant, but for others the edible parts are miniature themselves. These plants are not just cutesy wootsy (though they really are that), but they are also great alternatives to pump variety into any sized garden.
As a trial judge for the All-America Selections program, I’ve had the pleasure of trialing several plants over the last few years that are great for containers, including the 2021 AAS regional winner Pot-a-peno jalapeno pepper bred by Pan- American seeds. I’m excited that this year, a new trial has been added to the program to specifically trial plants for container growing, so be on the lookout for more container garden winners in the future.
Container-sized vegetables come in all shapes and sizes. Some of my favorites are ‘Patio Choice Yellow’ Tomato, which grows 18 inches tall and produces numerous yellow cherry tomatoes and the 2-ft tall ‘Patio Baby’ eggplant that produces 2-3″ eggplants (both plants are AAS winners). There’s the cucumber with only 3 foot long vines called ‘Patio Snacker’ and a 4 inch cabbage head named ‘Katarina’. You can find a fairly good list on this document I put together for my container vegetable gardening workshop:
Mini varieties of plants have even created some community-driven projects, like the Dwarf Tomato Project that uses a co-op type process where home gardeners are crossing plants in their own gardens to develop new dwarf cultivars of tomatoes.
Vegetable Garden, but make it Pretty
Gardens like this tomato, pepper, basil and flower combo are common on places like Pinterest
Many who grow container gardens like to make attractive gardens to decorate their porches, patios, and decks. Vegetable gardens can range from the utilitarian (like a tomato plant in a 5 gallon bucket) to the beautiful. There are lots of ways to mix plants to get a good container design if that’s what you’re after. Mixing color, shape, and form of plants can be done just as easily with vegetables as it can be with petunias and geraniums. You can add in flowers for extra pops of color as well. All one needs to do is search the internet (especially places like Pinterest) to find ideas for dressing up container gardens. I talk about container designs with vegetables in my recent talk (recording shared below) and the plant list I shared above.
Last month in my blog My Soil Is Crap Part I, I tried to dispel the myth that you can diagnose soil problems by just looking at your soil. While the color of a soil does impart some diagnostic qualities, most soils are not easily analyzed without a soils test. A complete soils test will give a textural analysis including useful information about water holding capacity and a variety of chemical analyses. Soil reaction or pH is an essential component of any soil test (and is often unreliable in home soil test kits). Soil reaction affects the availability of plant required mineral salts. Most soil tests give a measure of the salinity sometimes call TDS, or total dissolved salts (solids). Finally specific mineral content of soil is usually analyzed – in particular macronutrients are usually quantified. With these data a great deal can be predicted about the “grow-ability” of your soil. Soil tests can also help guide attempts to modify soils. The biology of soils is not easily or routinely analyzed through soils tests.
Soil Harm
Soil can be “harmed” in several ways–making it less able to grow plants. Or another way to look at this is that soil can be enhanced in several ways to grow plants better. First let’s examine the harm. Soil can be physically harmed by tilling with a rototiller. Tillage destroys structure and the natural clods and peds that form over time because of a soil’s innate qualities. Structured soils support plants and help prevent disease. Tilled soils will in time resume their native structure, but the amount of time required is quite variable depending on soil type. Soil structure can also be squished– this is compaction. Compacted soils hold less water, take water in slowly (so more runoff) and have less air space for gas exchange. In severely compacted soils roots have difficulty penetrating so plants don’t grow well or at all in compacted soil zones. Compacted soils are common in parks, school yards and public areas. Finally soils can be damaged chemically and biologically. Excessive salts from fertilizers applied in excess can compromise roots causing fertilizer burn. Soil residual herbicides from overapplication can have toxic effects on plants growing there or nearby. Herbicides and salts often accumulate along roadsides where they are used to melt snow and ice or control weeds.
Compacted, saturated or layered soils can build toxic gases that reduce metals in the soil, creating hazardous conditions for plant growth
Climate affects on soil
Climate can modify soils making them less than optimal for growing plants. In areas of high rainfall, soils may become deficient in certain ions such as metals, which tend to leach from soil, leading to increased acidity because these ions help maintain pH neutrality. In areas where precipitation is less than evaporation, salts tend to accumulate in soil and soil reaction rises above neutral. The ideal soil pH for most plants is 6.8. At this pH, most plant-required minerals are available for absorption by roots. As pH moves above 8 or below 5, soils are said to be alkaline or acid and various minerals are less available to plants. Soil reactions between pH 6.8 and 7.2 usually pose few problems for most plants. Some plants that are “acid loving” like blueberries are adapted to grow in low pH soils where nutrients are supplied by decaying organic matter. For these kinds of plants, some soil modification may be necessary (unless you live in a climate where such plants are natives). Testing your soil pH is very important to understand nutrient availability in general.
Amending vs Mulching
Arid soils are usually low in organic matter. In climates with more rainfall where forests or grasslands naturally occur, soils have higher organic matter content. Typically organic matter ranges between 1 and 5% of total soil solids. Organic matter supplies carbon for soil microbes and is necessary to promote soil structure. Organic matter can hold and release positively charged (cations) soil mineral nutrients used by plants. Organic soils have the highest cation exchange capacity (CEC), a measure of soil fertility. Soil organic matter tends to bring soil pH back toward neutral. Very acid or alkaline soils can be modified by adding organic matter. Finally, organic matter may contain nutrients that help plants grow. Sometimes amending with a nutrient-rich compost will give annual plants quite a boost (see Calendula images below) While arborist chip mulches yield nutrients to soils slowly over years, composts provide nutrients immediately, and they can be easily over-applied depending on what is required for a given soil to grow the intended plants. If you are going to amend a soil, be sure that the amendment has enough nitrogen in it. Well-formed composts, high in plant required mineral nutrients but not overly salty, make excellent amendments.
Adding amendment to planting holes of perennials is not recommended because it has little long term effect
Perennials, including all woody plants, generally do not benefit from amending because they rapidly grow out of the amended zone in the planting hole. Unless you amend an entire site, not much will happen. Also, once perennials are set in the ground you can’t amend again. Mulches of arborist chips, fresh or aged, are best for perennial plantings. Mulches can be replenished as needed without disturbing root systems. Raised beds are often amended heavily, and rightly so, since these planting situations amount to large containers that need a more porous “soil”. Since raised bed plantings are usually annuals, amendment can be added again as needed between crops. Composts make suitable amendments. Compost qualities, especially salinity, should be carefully measured or monitored before using, or through a bio-assay as detailed in my last blog.
Compost applied to clay soil.
No compost on a clay soil
Calendulas left and right are the same age
Adding minerals and fertilizers
Gardeners generally buy and add fertilizers without concern to harming their plants. This is a big NO. Excess levels of phosphate can interfere with uptake of other needed minerals. Applying fertilizer to landscapes above what is needed can pollute creeks and other bodies of water. It is important to let your soil test guide fertilizer applications. Usually there are enough fertilizer elements in most soils that landscapes can remain unfertilized, especially if leaf litter and mulches are utilized. If plants show deficiency symptoms be sure to check your soil reaction to make sure that the pH is in a growing range for the plants you are cultivating. If the pH is right but you still have symptoms, then consideration of fertilizers based on soils tests is appropriate.
There is some confusion about use of minerals as amendments. Lime is used to raise pH and often brings soils back into production in high rainfall areas where soils are too acid. Gypsum does not alter pH of soils but is often called things like “clay buster” or “compaction reliever” This is because salt affected clay soils have too much sodium which is replaced by calcium when gypsum is applied to a sodic soil relieving some of the particle dispersion. Most gardeners do not have sodic soils (which are greasy and poorly productive) but just plain old clay or clay loams. Gypsum supplies sulfate as an anion and calcium as a cation and if sulfur or calcium are deficient gypsum can be helpful. Gypsum is not needed in most gardens. Gypsum does have a fungicidal effect against root rot organisms (Phytophthora) and can be added to reduce root rot hazard. Epsom salts (magnesium sulfate) are often recommended for rose culture, but there is no research showing any benefit from their application to roses. In our trials in California, application of Epsom salts had no effect on rose bloom quality or quantity. Some soils low in magnesium could benefit from magnesium sulfate but these are fairly rare.
Some Soil changes are not long lasting
The textural nature of soil (i.e., relative amounts of sand, silt and clay) does not change over time. While we can add organic matter, it breaks down and disappears rapidly. Water quality, evaporation, and rainfall drive soil change. These factors tend to bring soil back to its “native” conditions. Irrigated soils may be affected by the quality of the irrigation water. So if you are trying to grow blueberries in Las Vegas, this will be a challenge that likely can’t be met by soil modifications. Growing plants adapted to the type of soil and climate you have is best. Growing exotics that require a different soil formation process will always be an uphill battle better suited to container culture.
References:
Blakey, D. 2021. Adjusting soil pH in California Gardens. UCANR publication 8710. https://doi.org/10.3733/ucanr.8710
Downer. A.J. and B.A. Faber. 2021. Organic Amendments for Landscape Soils. UCANR publication #8711.
Downer, A.J., and B.A. Faber. 2019. Mulches for Landscapes UCANR publication #8672.
Faber, B.A., A.J. Downer, D. Holstege, and M.J. Mochizuki. 2007. Accuracy varies for commercially-available soil test kits analyzing nitrate nitrogen, phosphorus, potassium and pH. HortTechnology: 17:358-362.
Messenger, B.J., Menge, J.A., and E. Pond,. 2007. Effects of gypsum on zoospores and sporangia of Phytophthora cinnamomi in field soil. Plant Disease 84(6): 617-621
If you’ve been around as long as I have, you will no doubt remember the Creedence Clearwater Revival song “Have You Ever Seen the Rain”. This week I want to talk about sensing the rain using radar and how you can use it to provide you with local rainfall information if you don’t have a rain gauge of your own.
Source: Brocken Inaglory, Creative Commons
How does radar work?
Radar is what scientists call an active sensor, because it sends out a beam of electromagnetic radiation that is reflected back to the radar if it hits something reflective like raindrops or hail (it also works on birds, insects, and cars traveling along interstates, but that’s another story). By detecting how much of the original beam is returned and how long it takes to get back, the radar can determine how much precipitation there is and how far away it is falling. The radar emitter usually rotates around a circle to provide a 2-dimensional picture of the precipitation in the area around the radar instrument. They can make it 3-dimensional by tilting the radar up at different angles to see different levels in the atmosphere. Now, the newest doppler radars used by the National Weather Service can also sense the size of the falling particles and how fast they are moving towards or away from the sensor. The radar displays that are usually used on television or online show a color-coded map with the brightest colors corresponding to the highest radar returns and thus the heaviest rain rates.
Source: Environment Canada
Radars can be used to estimate rainfall, but some assumptions must be made about the rain to get a good estimate. The major estimate that is needed is what size or sizes are the raindrops and how many of them are present. That will allow the radar software to calculate the volume of water that is falling and relate it to the strength of the return “echo” of the radar beam.
But how do they know the distribution of raindrop sizes in a rainstorm?
Source: Jason Zhang, Creative Commons
I learned this week in a video on raindrop shapes that the first person to measure rainfall size distributions was William Bentley, a citizen scientist in Vermont who is best known for his spectacular photographs of snowflakes. Bentley used a tray filled with a shallow layer of flour and exposed it to falling rain. The drops landed on the flour and dried into balls that provided a measure of how the size of the drops varied in the storm. Of course, now there are more sophisticated ways of determining this using optical sensors and other devices, but this was surprisingly good for its time.
William Bentley, photographer (public domain)
Today, by measuring the amount of radar emissions returned to the sensor and calibrating it to rain gauge measurements at the surface, atmospheric scientists have been able to provide good estimates of the rain falling across the region that the radar is able to sense. That is usually within about 120 miles before the radar beam overshoots most of the rain clouds due to the earth’s curvature. Fortunately, with a network of radars across the country, we can get a pretty good estimate of rainfall that is spatially much more detailed than we can get with a network of surface observers from the National Weather Service, state networks like the agricultural weather network I manage at the University of Georgia, or the volunteer corps of observers in CoCoRaHS (for more on this network, see https://gardenprofessors.com/the-weather-where-you-are/). That allows us to have a pretty good sense of how the rain is varying across fairly short distances and provides a reasonable estimate of the rain at your house if you don’t have a rain gauge available.
Radar-estimated rain where you are
To find the rainfall estimates for your location, the easiest way to do it is to use the National Weather Service’s Advanced Hydrologic Prediction Service. This website provides a daily rainfall amount based on radar estimates for the period currently from 8 AM EDT on the previous day to 8 AM on the day of the map. They are usually available an hour or two after that time period ends so they can receive the data and perform quality control before releasing the maps. You can zoom in on the maps to your location and add county outlines or other backgrounds to help pin it to your exact location. The site also allows you to look at 7-day, 14-day, and longer accumulation periods and to compare those to normal or expected precipitation. The map below is one I created for a heavy rain event in Georgia this past week on April 25, 2021, where a few locations in southern Georgia got up to 10 inches in just a few hours, causing problems for farmers there due to standing water, erosion due to runoff, and scattered loss of seed and fertilizer.
Radar-estimated rainfall for 24 hours ending at 8 am EDT on April 25, 2021.
The radar maps are not perfect. You can only zoom down so far, and the smallest unit is still at least a few kilometers or miles on a side, so you will never be able to distinguish the exact edge of a summer thunderstorm that drops rain on one side of the road and leaves the other side dry. The estimates also tend to be too low in high-intensity rainfall because the relationships that the radar software uses to estimate the volume of water don’t work very well when it is raining harder than normal. But by calibrating the rainfall to observers’ reports, they are usually pretty reasonable. If you are not in the United States, you will need to check with your own nation’s weather service to see what radar information is available.
Coming in May…
Speaking of “normal”, in May NOAA is expected to update the normals for temperature and precipitation for the US from the 1981-2010 values to the 1991-2020 values. The new temperature values will be higher than the previous ones due to the upward trend in temperature in the US and the globe over time. Rainfall will also change but it will go up in some places and down in others due to wet and dry spells in different parts of the country over time. I will talk about the new normals and how they are created in my blog post in late May.
Masses of spring bulbs transform this lawn. Photo by Charlotte Scott.
Nothing seems to take homeowners more time, or generate more frustration, than maintaining their lawns. In addition to mowing, fertilizing, and applying pesticides for weeds, insects, and diseases, gardeners fret about removing thatch and aerating the soil. Commercial interests have taken note and pedal various “aerifying” products like soap (cunningly described in non-soap terminology), spiked sandals, and thatching rakes. Previous posts (here and here) have addressed ways to decrease fertilizer and pesticide use. This post will look at the science behind aeration of home lawns.
Iron maiden torture devices in sandal form
More lawn torture via thatching rakes
That first ingredient in this aerifying product? It’s soap.
The home lawn care industry is lucrative and full of questionable things.
First, let’s acknowledge that most research has focused on maintaining turf on golf courses and playing fields. Neither of these are good models for home lawn management because home lawns have different functions. The turf that one might find on a putting green, for instance, is devoid of most life except for closely mown monocultural (or oligocultural) grasses. The management of these grasses is chemically and physically intensive to preserve a completely unnatural system. Yet these management techniques, including core aeration and vertical mowing (aka verticutting), have seeped into the lucrative home lawn maintenance market, especially to address the dreaded thatch layer common in many home lawns.
Live and artifical putting green turfs look alike. Neither is a good substitute for a home lawn.
What is thatch?
Briefly, thatch is caused by organic material accumulating at the base of grass plants. (It is NOT caused by lawn clippings, which are small and nitrogen rich – they are broken down quickly.) Accumulation of thatch is said to lessen lawn resilience and increase disease, but this appears to be a classic CCC (correlation conflated to causation) error. I’ve seen nothing in the literature to suggest that thatch causes these problems. Instead, I see evidence that thatch is yet one more negative result of poor lawn management. Removing thatch, without addressing the CAUSE of thatch, is an exercise in futility.
Lawn with thatch layer
Natural grassland
Look at these two images of grass-covered soil: one is a typical lawn, and the other is a natural grassland. There are no roots extending below the “thatch” layer in the lawn, while grassland soils support deep and extensive root systems. The problem with the lawn is that the system is not well aerated, meaning that the grass roots are shallow and contribute to the buildup of thatch. Lack of aeration also inhibits a robust community of microbes, which are necessary to decompose the organic material that makes up thatch.
If you have standing water on your lawn, there is no oxygen in the soil beneath.
So, lack of poor oxygen and water movement between the grass layer and the underlying soil creates a dead zone in that soil, with life restricted to those few inches of soil where oxygen and water can penetrate. Thatch accumulates and underlying roots from nearby trees and shrubs are forced upwards into the lawn to obtain water and oxygen. This is where lawn maintenance companies promise to fix the problem through core aeration or verticutting.
It’s not goose poop. It’s core aeration.
Vertical mowers look impressive but do they work?
Popularly recommended gadgets and gizmos
Does core aeration and verticutting improve home lawns?
While there is scant research on home lawns, the results are fairly uniform: core aeration does not reduce thatch accumulation and does not improve grass coverage. Verticutting can decrease thatch slightly but decreases grass coverage and reduces turf quality. Several quotes from published research stand out:
“All cultivation practices [which included core aeration and verticutting] resulted in some quality loss at various times during the spring transition period compared to the control.”
“Thus, under homelawn conditions, core aeration and vertical mowing should only be used if a specific problem exists and not as routine practices to prevent thatch accumulation.”
“After two years, no treatments consistently reduced thatch accumulation compared to the non-cultivated control.”
There is no published research, anywhere, that supports these techniques in maintaining healthy home lawns. So, it’s time to stop using these heavily promoted products and practices and instead focus on why lawns accumulate thatch in the first place.
It’s all about the oxygen!
There’s no question that lawns can be heavily compacted, but it’s not because grasses can’t tolerate foot traffic. Think about those hundreds of thousands of bison that use to roam the Great Plains grasslands. Even modern cattle ranching, done sustainably, does not damage pastureland by compacting the soil. There’s something else going on in home lawns that creates compacted conditions and the cascade of negative effects that follow; it’s improper soil preparation and management.
Pastureland dosen’t become compacted despite the significant pressure cattle exert on the soil.
When sod is laid for home lawns, several inches of compost are tilled into the soil bed. The tilled soil is then flattened with a roller, and then a layer of sand is applied. Then the sod (which consists of grass and growing media and a mat of some sort) is arranged. And voilà! You have a turfed landscape that more closely resembles a five-layer dessert than a functional grassland. Those layered materials restrict the movement of water and oxygen, and this restricts root growth into the underlying native soil. Not only do these barriers create a shallowly-rooted turf, they compound the problem by stimulating ethylene gas production in grass, further inhibiting root growth. To top it off, the anaerobic conditions in the lower layers restrict microbial decomposition. As decomposition and root growth slow, thatch accumulates. And homeowners despair.
All of these practices are bad for soil structure and function, and over time will result in an unhealthy lawn.
So, thatch serves as a warning sign that soil conditions are poor – and any attempts to permanently remove thatch without addressing poor soil preparation and management are going to fail. Possible corrective actions to improve soil structure and function are beyond the scope of this column; over the years we’ve had blog posts touching on this topic and I encourage readers to explore our blog archives.
