Way back in 2010 (and then again in 2012) I wrote about a bizarre belief that cornmeal could be used to treat fungal diseases, from lawn spot to athlete’s foot. Rather than rehash what’s already been written, I’ll invite readers to read those posts for background. And of course look at the comments, which are…interesting.The weird thing is that this post from 2010 is the single most popular post on the blog. (Our stats are only for the last two years since we migrated the web site – who knows how many there were before May 2017?)
The consistent popularity for the topic spurred me to publish a university fact sheet on the use of cornmeal and corn gluten meal in home landscapes and gardens. This fact sheet reviews the pertinent literature, and makes recommendations that are pretty much the same as those I made almost 10 years ago. Nothing has changed in the research world to support cornmeal as a fungicide.
But wait, there IS something that’s happened since 2010! Now cornmeal is being touted as an insecticide! In fact, if you go to Google and search for “cornmeal” and “insecticide” you’ll find thousands of hits. As you might expect, there’s no research to support this notion: researchers in Maine, for instance, found no effect of cornmeal on fire ants. However, it is used as a bait to deliver actual insecticidal chemicals.
But facts don’t get in the way of home remedies, such as Lifehacker’s eyebrow-raising advice.
By refining the search to only include university websites (use “site:.edu” to do this), and swapping out “ants” for “insecticide,” you’ll find at least one Master Gardener group happily (and illegally) recommending cornmeal as an ant killer. The popular mode of action is either (1) they can’t digest cornmeal and starve or (2) the cornmeal absorbs water in their gut and they explode.
This reminds me of yet another food product – molasses – recommended for killing ants. Since you’re already here, you might as well check out Molasses Malarkey parts 1, 2, and 3 too.
Might I recommend everyone use their cornmeal and molasses to make bread or cookies or pancakes? There are some delicious recipes on the internet.
Today’s blog post is courtesy of Mary Blockberger of Sechelt, BC. As you’ll see, Mary and I go way back. I thought it was important to our ongoing discussion to see how the industry can use the root-washing technique effectively and economically. Here’s Mary:
“Before I began managing the Sunshine Coast Botanical Garden in Sechelt, BC I had a small residential landscaping company. By small, I mean that I was the employee of the month every month of the year! One of our Garden’s mandates is to provide relevant and educational programs for our community. Dr. Linda Chalker-Scott has been one of our most popular speakers several times. One of her presentations dealt with the practise of bare-rooting perennials, shrubs, and trees prior to planting, and the tremendous advantages of following this method.
“In November, 2007 I had a chance to try this technique out. My client wanted a ribbon of Carpinus betulus ‘Fastigiata’ planted that would eventually be pleached into an interesting pattern. [Pleaching is a formal tree training technique.] There was a total of 36 trees to be planted; most were container stock as I recall but there may have included a couple of B&Bs as well. Working with another local landscaper, into a wheelbarrow of water went every single tree one at a time. The dirt was clawed away from the root balls by hand with a final spray from the hose. Honestly, it was a cold and miserable job, and I believe a few curses directed at Linda ensued. However, once the roots were cleaned of all soil planting was a breeze. It’s a lot easier moving trees without moving the soil too.
“Flash forward 12 years, and every single tree has flourished. Bare rooting allowed us to identify and correct any problems before planting, and I’m sure this has a lot to do with the trees’ success. It’s a time consuming and at times messy method, but the reward of a healthy row of trees is well worth the effort, IMHO.”
And let me add to Mary’s account that a ZERO replacement rate is going to pencil out to long term economic success. I was able to see these trees earlier this year – that’s my photo at the top of this post.
I think the blog and garden professors web page is pretty full of research and benefit descriptions of mulching, particularly with arborist chips. A little less clear is the role of amendments in garden soils. I always like to ask the “why” questions for gardening practices. Like “why” prune trees? Why fertilize, etc? Ideally gardening practices should be founded on a basis of science and inquiry as to their necessity. Poor structure early structural training or a damaged canopy may prompt tree pruning, mineral nutrient deficiency symptoms may suggest
fertilization. So why amend your garden soil? For me as a gardener you do this because your soil is not providing something you think your garden or plants growing in that soil need. This could be nutrients, or water. Amending as a soil or garden practice is best done in garden beds that host annual plants: vegetable gardens, color beds with annual plants etc. Obviously we are not going to lift all the perennials just to add some amendment under their root systems. We can also make arguments that amending soils that you are going to plant perennials in is unlikely to be helpful. So why amend?
Research on providing amendments in the holes of perennial plants has most often shown no significant differences compared to plants installed with just native backfill. There are lots of reasons for this and I can imagine some soils where amendments would give a slight boost, but these were not the soils most studies used (extreme sands). Mostly, perennial roots do not reside in the planting hole for long, so the time that amendments would be effective is very short. Since amending can also harm some plants if done incorrectly, University of California does not recommend the practice, neither did Harris for trees, shrubs and vines. Nor did we find any effect in palms (Hodel and others). For this blog we will assume that amending is restricted to annual plant beds. So why amend? The usual reason I hear is: “My soil is crap!” I think it would be interesting to survey people about their soil and see what they think about it as compared to how it actually grows. Most people seem to disparage their poor soil….So many gardeners believe that if they add something to their crap soil it will get better. Maybe, or no. Amending has potential benefits and detriments depending on what and how much you amend with.
So the potential benefits of amending are:
• rapid (immediate) modification of the planting bed
• potential increase of moisture holding capacity in the soil
• potential increase of nutrients and nutrient holding capacity (cation exchange capacity of the soil
• change in the soil texture, porosity
• rapid increase in soil organic matter
• suppression of soil borne pathogens
Potential detriments include:
• nutrient draw from the soil (nitrogen immobilization: see images above)
• toxicity from residual phytochemicals
• adding pests (weeds or root pathogens)
• soil structure is destroyed
• soil food web is challenged and harmed
• may increase soil salinity
• contaminants can be transferred to gardens
One of the incontrovertible facts about amending is that you have to disturb the soil to do it. Amending involves digging in, roto-tilling, soil turning with a spade, or some kind of incorporation process. Usually the more the better. This destroys soil structure and a good part of the soil food web. Beneficial nematodes are highly sensitive to tillage and many are killed by tillage, often perturbing the entire soil food web in a disturbed soil (See research by Howard Ferris). The beauty of mulching is that the soil structure is not initially influenced only assisted in its further development. The downside is that mulches take months or years to have their effect. While amending can give immediate physical, chemical and biological assistance to soil, it also may bring pathogens, salts, toxic phytochemicals or weeds to your garden depending on what you choose to use as an amendment. Soil tends to be very resilient, so structure destroyed by amending is usually back in place at the end of the cropping cycle in many cases. The need for further amending should be considered carefully after each rotation.
So you still want to amend? What do you amend with? In the case of mulching we (Garden Professors) make a strong argument for freshly prepared (not composted) arborist chips. Nothing could be worse for amending (at least in the short term). Un-decomposed substrates such as wood chips are high in carbon and low in nitrogen. They will cause the microbial community of soil to attack the carbon and utilize all the free nitrogen in the soil, screened or fine materials after composting have greater surface area and will enhance the water absorbing and nutrient holding properties they give to soil. Furthermore, well composted substrates or feedstocks will be free of pathogens and other pests so they should be “safe” for your garden. Composts that are made from plant feedstocks tend have concentrations of plant required minerals. Since composts lose about 2/3 of their carbon and moisture during the decomposition process they have a much higher mineral content than their feedstock. Manures have already been partially composted by the animals that made them. Additional composting increases their salt levels sometimes to plant damaging levels. Manures should be used with care, or in lower quantities as they can damage sensitive plants. Some manures and composts can be contaminated, since some long term soil-residual herbicides such as clopyralid are not broken down in the composting or animal eating process.
Gardeners are inventive in their use of compost and amendments, so there are many ways to amend soil. Peat moss has been the gold standard amendment for many gardens. However due to environmental damage, sustainability of peat moss use is questionable. Coco fiber or coir is a good amendment, but it can bring high salts with it depending on how it was processed. Biosolids are phenomenal amendments and often produce growth responses, but there can be issues with metals and other biological contaminants in biosolids. Home-made compost is a good amendment because you know what is in your compost, as long as it is properly prepared and cured, it can function very well. Greenwaste or yardwaste compost is a possibility, but from my experience, most of these if commercially produced are not well prepared, and are not mature (they still heat up if piled). Many gardeners like coffee grounds, and with the advent of large coffee companies, grounds may be available in bulk quantities. Be careful though as some sources of coffee are toxic to many plants and their use should be limited in any amending situation.
What about rate? In my research I have always tried to amend soils 50% by volume. So a three inch layer of amendment tilled six inches deep has been my goal. Most annual plants have their roots in the upper six inches and this strategy works well. Also, most rototillers are only good for about a six inch depth. If you intend to dig deep with a spade and incorporate to depths beyond six inches, increase the amounts accordingly.
What kind of soil needs amending? Another way to view this is, “have you tried growing without amending? Many soils grow very well with just added nutrients. Typically sands will most benefit from added amendment due to increased water and nutrient holding capacity. I also like to amend clays because they become easier to plant in over time, however the initial go round may be difficult. Clays are very nutritive so amendments may make you feel better gardening in them, but often plants grow very well without amending clay soils. Plant responses to amendments are best in sands.
How often should I amend? This is up to you, but organic matter is “burned up” by the soil microbial community rapidly because 1) you are tilling and this accelerates microbial activity; and 2) you are likely amending during the growing season when warm soil temperatures favor organic matter breakdown. Most gardeners amend prior to replanting the bed.
Ferris, H., and M.M. Matute. 2003. Structural and functional succession in the nematode fauna of a soil food web. Applied Soil Ecology 23:93-110
Harris, R.W. Arboriculture: Integrated management of landscape trees, shrubs and vines. 1992. Ed. 2 Prentice-Hall International, New Jersey. 674pp.
Hodel, D.R., Downer, A.J., Pittenger, D.R. and P.J. Beaudoin. 2006. The effect of amended backfill soils when planting five species of palms. HortTechnology 16:457-460.
“Why don’t you just plant it up against the house,” piped my mother-in-law. She was talking about a run-of-the-mill “old fashioned lilac” that we had received in the mail for our donation to Arbor Day. While I don’t necessarily think of the organized tn as a source of high-quality or novel plants, I felt beholden to make a donation since it was founded and is still located in Nebraska (and we have visited the Arbor Lodge, home to founder J. Sterling Morton and his brood of tycoons (one of salt fame – that Morton, one of cornstarch fame – ergo we have Argo, and one of the railroad). I had pawned the 10 blue spruce off to the freebie table at the office, but she wanted a lilac…and what momma-in-law wants, momma-in-law gets.
I explained to her that the labeled final size of the cultivar was 12 feet in diameter, so it needed to be at least 6 feet from the house (preferably more) and from other plants. “Nonsense!” she decried, “I planted mine close to the house. You just have to keep it pruned back. Mine did just fine….. until it rotted.” Since the right spacing would put the shrub in the middle of a narrow passage between the house and the fence, I opted to throw it into a pot since I was heading out of the country the next day for two weeks. It was, after all, a little more than a spindly twig (with roots wrapped together in a ball) sheathed in plastic.
What’s the issue?
Most gardener’s desire for instant gratification often means that correct spacing for the finished size of the plant gets thrown out the window so that the garden looks good to go from the beginning. Or even worse, plants get shoved against houses, under power lines, or in other areas where they’ll either be cramped and crowded or incessantly pruned to the point of oblivion throughout their probably shorter-than-expected lifespan. Think of it like your bubble of personal space. Just like you don’t want to be crowded, neither do plants.
In addition to the pruning and space issues, crowding can increase the likelihood of disease or other plant issues. Crowded plants reduce air flow, which aids the development of diseases by increasing (ever so slightly) the humidity in the plant’s microclimate, increasing drying times after rain or irrigation, and even allowing for disease spores to more easily settle on the plants. For perennials, and especially trees and shrubs, overcrowding can be a chronic issue since the problem can last for many, many years.
That’s not to say that spacing it isn’t a problem with annuals, either, especially in the vegetable garden. In addition to the increased possibility of disease, competition for space and for nutrients can reduce yields. Crowded root crops like carrots, beets, and radishes don’t have enough space to fill out, resulting in stunted and irregular produce. The same goes for leafy crops like lettuce or kale. Fruiting crops like tomatoes and peppers can also suffer from reduced production when plants can’t fully grow to their potential.
Getting Spacing Right: The Simple Art of Not Planting Too Damn Close
Perhaps the secret is complicated formula for figuring out the proper plant spacing? Or perhaps it is some specific planetary alignment you need to wait for? Since it seems to mystify may gardeners, spacing must be difficult, right? Au contrare!
Most plants come with the proper space printed right on the label! Think of such a novelty! That lilac my MIL wanted to plant against the house said right on the packaging that it generally grew to 12’ wide. If I were planting a bunch of them in a row (and not as a hedge), I could plant them 12’ apart. If I wanted to grow them as a hedge, I’d reduce that spacing to make them grow into each other (but it will take time for them to grow into a hedge…so they won’t be touching right away). Keep in mind that this is the genetic potential of the plant and isn’t a guarantee. Many factors, including microclimate, soil conditions, precipitation, nutrient availability, disease, etc. etc. etc. could limit the plant’s growth to that potential (or even more rarely increase it). What if I’m not planting a bunch in a row? Here’s were a teensy bit of math comes into play.
Think of plants in general terms as circles. Just look at a basic landscape architect’s plans and you’ll sometimes see plants represented generally as circles. If you think all the way back to that geometry class in high school, you’ll remember that there are several measures of a circle, including the diameter and the radius. The diameter is the width of the circle from one side to the other. The radius is the distance from the center point of the circle to the edge. So if our plant is a circle, then the listed width of the plant is the diameter and the distance from the trunk, stem, or center is the radius. So I can expect my lilac (if it reaches full potential) to grow out 6 feet from the trunk. That means I need to plant it at least 6 feet away from the wall. If I wanted to plant it in the landscape with other plants around it, I would need to figure out the radius of the plants I wanted to plant close to it and add their radius to the lilac radius to figure the minimum distance I should plant them apart. Let’s say I wanted to plant a small shrub beside the lilac with listed width of 10 feet. That means the radius of that shrub is 5 feet. Adding them together, I get a distance of 11 feet. On the other side of the lilac I want to plant a large perennial with a diameter of 4 feet. The radius would be 2 feet, so my minimum planting distance would be 8 feet. You also have to keep in mind any variation due to microclimate and environmental factors.
What about the vegetable garden?
The same concept holds true for the vegetable garden as well – think of each of the plants as a circle. Where planning the spacing is different is usually interpreting what the seed packet says in terms of in-row versus between-row spacing. The in-row spacing is based on the size of the plant, a general idea of the size of the circle the plant makes or how much space it needs between plants (some plants, like beans, are OK when they overlap a bit and share space). The between-row spacing is for human use in creating typical in-ground, large garden areas. I’ve had the discussion before of large garden area vs. in-ground beds, vs. raised beds so we don’t need to go into that detail, but the general movement is toward some sort of bed system to reduce walkways (reducing bare soil that can lead to erosion or compaction when walked on) and intensify plant spacing/output per a given area.
Taking that into consideration, use the in-row spacing as the between plant spacing in all directions. This is what the popular Square Foot Gardening method does – the spacings and number of plants per square are based on the between plant spacing and eliminates row spacing. For example, radishes and carrots typically have an in-row or between plant spacing of 3 inches. If you fit that spacing evenly within a foot row segment, you get four plants. When you make that two dimensional you get 16 plants per square foot. For four inch spacing you get 3 per foot and 9 per square foot, six inch spacing you get two and four, etc. You can fill an entire bed with plants like this without spacing between rows of plants.
Of course, the tricky thing is that, just like our trees and shrubs that are planted too closely reduced airflow and increased microclimate humidity can increase the risk of diseases in the plants. The Square Foot Gardening method by the book states that you shouldn’t plant any adjacent square with the same crop to decrease likelihood of disease sharing, but that seems sounder in theory than in practicality. I use some of the spacing (and you don’t need the book, just look at the between plant spacing and calculate. You just have to monitor, use good IPM, and treat or remove issues promptly to reduce disease issues. Using interplanting to intensively plant by mixing various space usages (tall plants with short plants, root crops with fruit crops) can also help make use of the space while mixing plants to reduce disease spread.
Anyone who plants or cares for woody plants eventually hears the term “root flare” (or root crown). It’s easy to describe a root flare (it’s the region where stem or trunk morphs into roots). What’s sometimes difficult or even impossible is finding it in improperly planted trees and shrubs.
One of the primary causes of tree and shrub failure is improper planting depth. This is not a problem with bare-root plants, as you can easily see the region of transition. During planting you should make sure that the root flare is at grade, so that the roots are underground and the stem/trunk is above ground. The only mistake you can make with bare-root plants is to plant them upside down.
The problem really started with the advent of containerized and balled-in-burlap (B&B) plants. This technology is less than 100 years old, and before it existed everything was either planted from seed or from bare-root stock. It’s possible to use containers and B&B properly for temporarily housing trees and shrubs, but increasingly automated production methods with unskilled workers and undereducated supervisors means increasing numbers of poorly planted woody plants entering the retail market.
I’ve written earlier posts about how to select plants at the nursery. As you’ll note, finding the root flare can often be impossible without removing container media or B&B burlap. Because so many people are unaware of the problem or unwilling to disturb the root ball, these plants are then installed with the root flare still buried.
Why does it matter if part of the trunk is underground? For some species, it really doesn’t matter. Wetland species, for instance, can tolerate low soil oxygen levels and submerged trunks. But most of us are not planting wetland species, and many ornamentals are not tolerant of this treatment. Roots that are buried too deeply don’t receive enough oxygen to survive, and the plants respond by trying to create a new root system. These adventitious roots are unable to supply enough water to the growing crown, however, meaning shrubs and trees suffer chronic drought stress when the rate of evaporation exceeds the ability of these substandard root systems to supply water.
There are other problems, too. Stem and trunk tissues of non-wetland species are not adapted to being buried. The excessive moisture and lack of oxygen contribute to the attack of opportunistic pests and diseases, both of which can cause irreversible damage and eventual death. You can even see this happening to plants in the nursery.
Finally, consider this landscape evidence of the impact of buried root flares. These magnolias are all planted on the campus at Princeton University. The one of the left is significantly smaller than the other three. A close up of the trunks explains why.
If you have newly planted trees that look more like telephone poles than trees, the best thing you can do is dig them up and plant them correctly.
One of the “advantages” of being in the same office suite as me is hearing (a) that arborist wood chips are about as close to a miracle product as you can get and (b) that landscape fabric is hell on (the) earth. So my office mate Liz, either because she was convinced of the above or just wanted to shut me up, decided to rip out the landscape fabric in her ornamental bed and replace it with wood chips. She even made it a family project, somehow convincing her two young daughters that this was “fun.” Here’s her pictorial essay of the process.
Before the switch
Why on earth does anyone still believe that “weed block” fabric actually does anything remotely related to controlling weeds? It provides a great substrate for all those weed seeds blowing around, which find themselves the recipients of any rainfall or irrigation. They germinate and grow like crazy – because they are WEEDS. It’s what they do.
Worse yet for the soil – all of those pores in the fabric that supposedly allow water and oxygen to move through are soon filled with bits of soil. The resulting mat is anything but permeable. But weeds love it!
First Liz had to score some woodchips, which as you can see pretty much filled her driveway. The girls, however, thought they were a great addition.
Next, all of that fabric had to come out. This is not an easy process, because the surface of the fabric was completely colonized by weeds. A mattock is a great tool for getting this done.
Now, let’s look at the soil underneath the fabric. You can see how dry it is. That’s because even during our rainy springs in the Pacific Northwest all of the rainfall stays on top of the fabric, allowing lush weed growth. The roots of all of the landscape plants get virtually none of this, and in the summer that’s a source of chronic drought stress.
Fortunately, the soil underneath, while dry, looks pretty good. Once the shrubs and perennials are able to take advantage of the increased water and oxygen they will thrive.
Maybe you don’t like the look of arborist wood chips, but it’s certainly better than the weedy mess that used to be there. Plus, the soil benefits from the increased water and oxygen, the beneficial microbes in the wood chips, and the slow feed of nutrients as those chips slowly decompose.
If you are ready to switch from “fabric fail” to “wood-chip win,” you can start with this fact sheet which will guide you through the process.
Ok. I admit this blog is going to turn into a rant pretty quick because there seems to be a lot of ways to screw up a fairly simple horticultural practice—tree planting. Since Arbor days are happening/happened everywhere around now, its a good time to talk about how to plant trees. First let me state some simple and useful guidelines for a successful tree planting.
-When at all possible, plant trees bare-root. Even washing the container media away. This allows for inspection and removal of root defects.
-Select trees carefully that are free of defect and disease and that are adapted to your climate and soils
-Plant the youngest tree you can
-Take care in choosing the planting site.
-Avoid Root Barriers
-Plant trees so that the root flare is above ground slightly
-Plant trees in a hole only deep enough to contain the root system, no double digging.
-Plant trees in a hole wide enough to contain the root system, no wide holes (unless there is a reason for using one)
-Fill the hole with soil removed to make it. Do not amend the backfill around newly planted trees—Do not put rocks in the bottom of a planting hole!
-Plant trees without staking unless there is a reason to stake them
-Plant trees away from turfgrass or other groundcovers.
-Plant trees under the cover of a fresh layer of arborist chips.
-Irrigate newly planted trees from the surface—Do not install U tubes or tree snorkels to irrigate deeply.
I guess this rant comes from the variety of tree planting specifications I have seen over the years used by municipalities, landscape architects, nurseries and others. There seems to be a need to use the latest product, method or modification to site soils in order to make a fancy planting detail. Simpler is better and research by Universities has not verified most of the “innovative” approaches seen in planting details.
The first step in planting a tree is to chose the tree you want to plant. While this seems simple there is a lot that goes into tree selection. Setting aside personal choices, it comes down to selecting a tree that is healthy and free of defect. The potential candidate tree should have no signs or symptoms of disease, a naturally developed canopy unfettered by nursery pruning (especially heading cuts), and has few or no root defects. Initial superficial examination of the root collar in the nursery can eliminate some trees with circling or girdling roots. However, when the tree is planted root washing will reveal the entire root system and as Dr. Linda Chalker Scott has shown in this forum, root washing allows for rapid establishment in site soil. When at all possible chose the youngest tree you can for the new site. Young trees have fewer root defects, and we have the advantage of training them (structural pruning) from an early age. Young trees establish rapidly and will often outgrow older, boxed trees. The larger the specimen that you plant, the more chance for establishment problems such as settling, drying out, root rot or just slow growth. Planting trees from seed is ideal but most gardeners don’t have the patience to wait and seedlings, and seedlings do not give the option of using cultivated varieties that impart horticultural value, such as predetermined flower color, disease resistance, and known form (canopy shape and size).
Once the tree is selected, purchased and root washed, it is time for setting it in the ground. The first step is choosing a good planting site. A good site for a tree is somewhere that provides adequate soil volume for its roots to expand and for its canopy to expand. Many trees in urban settings fail to achieve their potential because they have restricted spaces to grow in. Chose a location in full sun. Unless you are planting a species that grows well in shade or needs protection from the environment, most trees will grow best in a sunny location. While trees are forgiving of most soil conditions, they will not grow well in compacted soils. If this is all that is available, break up compacted soils before planting. Consider the ultimate size of the tree you are planting, and imagine it attaining that size in your planting site. Avoid sites that have close proximity to buildings or hardscape. One of the most frequent problems with trees is that as they attain mature size they conflict with the infrastructure at the site.
Dig the hole for your tree so that the roots are very slightly above the grade. Do not double dig! While double digging has its proponents, there is no research-based reason for destroying soil structure– it is a disaster for tree planting. When a hole is dug too deeply soil will always settle after planting and irrigation resulting in the tree being planted too low in the ground. The root collar is buried and this is a predisposing factor for disease. The hole should have undisturbed soil under the roots. The hole only needs to be as wide as the root system. While many planting details show wide holes these are not necessary in most garden sites. If the site is compacted, wide holes can give temporary advantage to a newly planted tree, but the width of the hole will be the size of the “pot” the tree will have to grow in. So it is better to modify the site first to take care of compaction and then you will not need a wide hole.
Root barriers were very popular and are still specified today. They actually do not usually achieve thier goal of preventing surface roots and protecting infrastructure. Trees outgrow root barriers and they result in increases of landscape trash/pollution. Root barriers can also create root defects such as circling and girdling roots. Do not install root barriers, if you are tempted to do so you are likely not choosing a good site to plant a tree.
Cover the roots with backfill from the hole. Do not modify the backfill. Research does not support adding amendments to planting holes for trees. The native soil is what the tree will be growing in ultimately, and there is no reason to modify it. If the soil at your site is so bad that it needs to be changed, this should be a site-wide soil modification that will cover all the area the tree roots will explore up to its maturity. Most gardeners are not able to do this. Roots rapidly expand beyond the planting hole within months, so the time and benefit derived from an amended planting pit is minimal. Adding amendment, especially organic amendments to backfill can also be disastrous for trees. The organic material may utilize nitrogen in the soil and lead to a deficiency in the newly planted tree, worse, it may break down and cause anaerobic conditions in the bottom of the planting pit. Avoid amending planting holes! Never place rocks in the bottom of the hole—this does not create drainage, but creates an interface that prevents it.
If you have selected a good tree, it will stand without staking. There are three reasons for staking: support; anchorage; and protection. Support is sometimes necessary when a tree is cultivated with a long un-tapered trunk and a lollipop crown. Lollipop trees are often sold in nurseries as they resemble small trees. Trees trained in this manner, will not stand without staking. Loose staking allowing trunk movement will foster development of caliper so the tree can eventually stand without supportive staking. Anchor staking is used for trees that experience high winds and “staked out” with guy wires and a non-constrictive collar. Protective staking is analogous to placing bollards around a tree prevent impact from machinery or cars. Always remove the nursery stake at the time of planting and provide any additional support the tree may need. Many Cooperative Extension services have publications on how to stake a shade tree.
Avoid planting trees in lawns. Turfgrass and trees conflict with each other. Trees shade turfgrass which results in a thinning sward and increased disease prevalence. Turfgrass slows the growth of trees in an attempt to limit their shading effects. Turfgrass is a very competitive water user and trees will be deprived of moisture and nutrients if turfgrass is present. If trees must be planted in lawns, maintain at least a 1 yard radius around them with no turfgrass.
It has become a common practice to add irrigation or aeration devices to tree plantings. Sometimes called a tree snorkel these plastic 4 inch U tubes are buried below the root zone. Kits can be purchased from Box stores, and architectural details have been drawn specifying their use. Work by UC researchers showed that oxygen does not diffuse far from aeration tubes. So utilizing tree tubes to increase air flow is suspicious. Some planting details specify adding irrigation to the tubes to force a deep rooted condition in the tree. This places water below the root system, which can dry out and compromise establishment—not a good idea… Worse of all tree snorkels are sometimes installed with no purpose at all other than that was what the planting plan indicated. This is a needless practice and results in landscape pollution. Long term, tree snorkels are ugly, easily broken and provide no useful function to an establishing landscape tree. It is not in the nature of trees to proliferate absorbing roots deep in soil and snorkels will not change a tree’s genetics.
After the tree is set in its hole, and backfill settled in with water, apply a 4 inch layer of arborist chips as far out from the trunk as feasible—at least several feet. The chips will modify the soil improving, chemical, physical and biological properties while conserving moisture from evaporation, preventing runoff, and germination of annual weeds. Generally trees thrive under mulch as it simulates litterfall, or accumulation of organic matter under their canopies. Replenish the mulch as it deteriorates. Finally apply irrigation as needed through the mulch from the surface of the soil. This will help establishing roots, leach salts, and move mulch nutrients into the soil profile. Avoid companion plantings near the main stem of the tree and avoid piling mulch around the tree stem. Following these guidelines will lead to a healthy and useful shade tree that provides its many services for decades.
“Can I use manure to fertilize my garden?” That’s a common question we get in Extension and on the Garden Professors page. The answer is absolutely, but there’s a “but” that should follow that answer that not everyone shares. And that is…but for fruits and vegetable gardens the manure you apply could be a potential source of human pathogens that could make you or your family sick. There are procedures and waiting periods you should follow to reduce the potential risk to human health from pathogens in manure and other animal products.”
First, application of manures to garden and farm production spaces is a good use of nutrients and provides a way to manage those nutrients to the benefit of growers and the environment. Using the concentrated nutrients in the manures to grow crops reduces what washed downstream in the form of pollution. In addition to adding nutrients to the soil, application of manure and other animal byproducts (bone meal and blood meal, for example) add organic matter to the soil, which improves soil texture, nutrient retention and release, and supports beneficial microorganisms.
For organic production, both in home gardens and on farms (certified organic or not), manure and animal products are an important input for fertility. For the most part, manures offer a more concentrated (higher percentage) of nutrients by weight than composts composed only of plant residues, so less is usually needed (by weight) than plant composts to apply the same amount of nutrients.
While the nutrient levels of manures and composts can be highly variable, there are some general ranges that you can use to plan your application based on the needs you find in your soil test. (And you should be doing a soil test, rather than just applying manure or compost willy-nilly. Just because the nutrient concentrations are lower than a bag of 10-10-10, you can still over-apply nutrients with composts and manures).
So what are the hazards?
As you’ve probably realized from bathroom signs and handwashing campaigns, fecal material can carry a number of different human pathogens such as E. coli and Salmonella. The major risk around application of manures to edible crops is the possible cross-contamination of the crop with those pathogens. The number one hazard leading to foodborne illness from fresh produce is the application of organic fertilizers – mainly manure, but also those other byproducts like blood meal and bone meal. Add in the fact that the consumption of raw fruits and vegetables has increased over the last decade or more, and you’ll soon understand why Farmers who grow edible crops must follow certain guidelines outlined in the Food Safety Modernization Act (FSMA, which you’ll hear pronounced to as fizz-mah) to reduce the potential risk that these pathogens pose to people who eat the crops. Right now, only farms with a large volume of sales are required to follow the guidelines, but smaller producers are encouraged to follow them as best practice to reduce risk and liability. And while there isn’t a requirement for home gardeners to follow the guidelines, it is a good idea to understand the risks and incorporate the guidelines as best practice. It is especially a good idea if the produce is being eaten by individuals who are at higher risk of foodborne illness – young children, the elderly, or those who are immunocomprimised.
The recommendations are also suggested when there’s contamination from unexpected or unknown sources like when vegetable gardens are flooded (click here for a recent article I wrote to distribute after the flooding in Nebraska and other midwestern states).
Recommendations to reduce risk
As previously stated, while these recommendations have been developed for produce farmers, research showing the potential hazards of applying manures means that it is a good idea for home gardeners to understand and reduce risks from their own home gardens.
The set of guidelines outlined by FSMA cover what are called Biological Soil Amendments of Animal Origin (BSAAO – since we government types love our acronyms). Here’s the “official definitions” used in the rules for produce farming:
A Biological Soil Amendment is “any soil amendment containing biological materials such as stabilized compost, manure, non-fecal animal byproducts, peat moss, pre-consumer vegetative waste, sewage sludge biosolids, table waste, agricultural tea, or yard trimmings, alone or in combination”.
A Biological Soil Amendment of Animal Origin is “untreated: cattle manure; poultry litter; swine slurry; or horse manure.”
For BSAAO (we’ll call it raw manure), manure should only be applied to the soil and care should be taken not to get it on the plants. There’s also a waiting period between applying the manure and when you should harvest the crop. The length of the waiting period depends on whether the edible part of the crop comes in direct contact with the soil. Right now the USDA is still researching the appropriate waiting period between application and harvest, so the general recommendation until then is to follow the standards laid out in the National Organic Program (NOP) standards. Research shows that while pathogens may break down when exposed to the elements like sun and rain, they can persist for a long time especially in the soil.
For now, here are the recommendations:
For crops that contact the soil, like leafy greens (ex: lettuce, spinach, squash, cucumbers, strawberries) the suggested minimum waiting period between manure application and harvest is 120 days.
For crops that do not contact the soil (ex: staked tomatoes, eggplant, corn) the suggested minimum waiting period between manure application and harvest is 90 days.
For farmers following FSMA, the waiting periods could change when the final rule is released – some early thoughts are that it could increase to 9 – 12 months if the research shows a longer period is needed.
What about composted manure? Is it safe? The guidelines indicate that there isn’t a waiting period between application of manure that has been “processed to completion to adequately reduce microorganisms of public health significance.” But what does that mean? The guidelines lay out that for open pile or windrow composting the compost must be maintained between 131°F and 170°F for a minimum of 15 days, must be turned at least 5 times in that period, must be cured for a minimum of 45 days, and must be kept in a location where it can’t be contaminated with pathogens again (animal droppings, etc). Farmers have the added step of monitoring and thoroughly documenting all of the steps and temperatures. Now we know that that’s a bit of overkill for home gardeners, but suffice it to say that the cow manure that’s been piled up to age for a few years that you got from the farm down the road doesn’t meet that standard.
“Aged” manure ≠ “processed to completion to adequately reduce microorganisms of public health significance.” So unless you know for sure that you’ve reached and sustained the appropriate temperatures in your compost, you should assume that it would be considered a BSAAO subject to the 90/120 waiting period. Bagged manure you buy at the garden center is likely to be composted “to completion” or may even have other steps to reduce pathogens like pasteurization. Sometimes the label will indicate what steps have been taken to reduce pathogens, or even state that it has been tested for pathogens.
The recommendations also specifically mention compost teas and leachates (a topic we handle with much frequency and derision here at the GPs, since there’s not much science to back up their use and I mention here with much trepidation). For the sake of food safety, any tea or leachate should only be applied to the soil, not the plant. And for home compost that doesn’t even contain animal manure the 90/120 day waiting period should still be observed in most cases since some of what goes into home compost is post-consumer. Since we put pieces of produce in there that we’ve bitten from or chewed on (post-consumer), plus some animal origin items (eggshells) there’s the potential that we could contaminate the compost with our own pathogens – and the environment is perfect for them to multiply.
The Bottom Line
While these guidelines and rules for farmers may just be best practice recommendations that we can pass on to home gardeners, common sense tells us that taking precautions when applying potential pathogens to our edible gardens. An ounce of prevention is worth a pound of cure, especially when were talking about poop.
Over the last couple of weeks I’ve been in London having some unforgettable garden experiences. Thanks to the generosity of my UK colleagues Glynn Percival and Jon Banks I was treated to Kew Gardens, RHS Wisley Gardens, and Windsor Castle. I hope to construct several blog posts from these visits, but today’s post is an homage to the English garden meadow. Instead of monocultural turf lawns, mowed and sprayed into submission, why not consider a more biodiverse and visually pleasing approach to groundcover?
As the title of this post suggests, this is not a new topic in our blog. (You can read other related posts here, here, and here.) What was so stunning about these garden meadows (meadow gardens?) was the scale and effortless beauty. For instance, consider this tree-lined parkway at Kew, covered with English daisies.
I saw my first honest-to God cowslip in a meadow garden at the British Museum of Natural History.
How about these adorable tiny daffodils and checker lilies?
And here they are en masse.
This isn’t to say that the formal lawn isn’t a thing in England, It is.
But unless you have a castle, a baseball diamond, or a putting green to manage, why not consider something more appealing, not only to the eye but to your beneficial wildlife?
Understanding the mysteries of plant diseases: Prevention, Control and Cure (Part 3 of 3 in this blog series)
You’ve done your research and made a diagnosis—now what? Sometimes the plant has to be removed and never planted there again. Start over, do something else.
Controlling plant pathogens or abiotic disorders can be daunting, frustrating, even impossible. As I mentioned in the last blog early detection gives more options for control because the disease has not advanced to a degree where it can not be controlled. Controlling plant diseases is not just palliative (treating your plant’s pain) it involves understanding where pathogens come from, stopping their movement, arresting their development and preventing their spread. Understanding genetics of resistance can offer amazing control of diseases, and finally biological control limits the development and spread of many pathogens.
What Can What Can’t?
There are some battles that can’t be fought or fought easily with plant pathogens. When plants are infected with viruses, there is almost no control option but removal (roguing). All plants likely contain some kind of plant virus; but not all viruses in plants cause symptoms of disease. Dangerous viruses like tomato spotted wilt, impatiens necrotic spot virus, cucumber mosaic virus, or many others, are devastating to their hosts and once infected there is no controlling these. Removing infected plants at the first symptom of viral involvement is prudent but often infections have already spread. Viral pathogens almost always infect without significant symptoms, and become systemic in the plant before their more
devastating effects become visible. By late season, in most vegetable gardens, viral titre (concentration) is very high in solanaceae plants (pepper, tomato etc) and in cucurbits, both groups are highly susceptible. When perennial plants get viral pathogens there is no cure, and symptoms will increase over time. In orchids, viruses can sometimes be avoided by tissue culturing the meristem (which is usually virus free) to clean up a rare plant worthy of salvation. Sometimes plants are already dead but don’t look it. In the case of root rotted trees and shrubs, leaves may still hang from the tree, may still be green but the tree is beyond salvation, control may not be possible. In general control measures are best conducted early. And by early I mean before you obtain your plant!
An old adage goes: “An ounce of prevention is worth a pound of cure” This is especially so when there is no cure!. Prevention as a control technique really involves several factors such as exclusion, quarantine, and maintaining plant health so that plants are not predisposed to disease. The first tenet of control is exclusion. Don’t bring pathogens to your garden. Gardeners are their own worst enemy where plant diseases are concerned. Since pathogens can be seed-borne, come with insects, be already infected in the nursery, or resident in soil, care must be exercised when new plants are selected for your garden. Practice safe plant swapping! Gardeners sharing plants with each other may also be sharing their respective plant diseases! Be careful where you buy plants, sloppy nurseries with their plants on the ground in standing water is a red flag. Also be on the look out for weeds in nurseries since they can harbor insects that vector virus diseases. Plant debris left on the ground and not cleaned up, can be a source of fungal spores. So consider the source when selecting plants for purchase. Inspect plants carefully before purchase, especially slipping the container off to look at the root
system. I don’t purchase anything (even boxed trees) without doing this first. If you are satisfied that you have a healthy plant then you are ready for the next phase of disease control.
Plants are often quarantined before they are released for cultivation or planting. When you bring your plant home, leave it in the pot for some time. Even bedding plants if purchased young can grow for a bit in containers. Remember lack of growth is a symptom of incipient disease. Observe your new purchase of a few days or even weeks depending on the plant. If normal growth is occurring then move on to garden placement and planting. A little time set apart from other plants, and careful observation, will possibly prevent bringing something bad to your garden.
Once disease is established, and symptoms are apparent, gardeners often turn to pesticides to try to provide therapy. Sometimes fungicides applied to a plant post infection will slow down the spread of the pathogen within or on a plant. Therapeutic approaches can also turn on plant defense systems or enhance them so that the plant can limit the progress of disease. Therapy is usually not an option with most diseases because the pathogen has often gone beyond the point of stopping it by the time disease is recognized. Some fungicides applied early, can be very therapeutic in turfgrass diseases, blights and powdery mildew diseases. The key to therapy as a control option is to detect the disease early and use an efficacious material that is labeled to control the pathogen you think is causing the disease on a given plant. All this should be on the label.
An immediate response of many gardeners when disease is discovered is to kill the pathogen. This is eradication. Eradication takes several forms. There are eradicant pesticides, that kill the pathogen on contact. Usually these cause some degree of harm for the host since most pathogens have a host relationship that is destroyed when the pathogen is killed. Eradication can also be or removing plants from the garden that are a source of disease. Picking up and disposing of fallen plant debris is eradicating a source of potential inoculum from the garden. Pruning cankered branches from a tree is a form of eradication.
One of the best forms of disease control is resistance. Selecting plants that resist disease is built in control. Diseases such as rust and powdery mildew have wide ranges of interaction with their hosts. By selecting plants that are resistant, there is no need for other control measures such as sprays. Resistance to plant disease comes as two types. Horizontal or multigenic resistance is partial or incomplete resistance and is conferred by several genes or their interactions in the host with the pathogen. Vertical or complete resistance is resistance conferred by a single gene in the host. Plants with horizontal resistance will get some of the disease but it won’t be overwhelming, often in grains, lack of resistance will result in complete crop failure. Plants with vertical resistance show no symptoms and are completely immune to the pathogen. While this complete resistance is appealing, it is only conferred by a single gene, and the pathogen can easily break down this resistance and cause disastrous disease. Horizontal resistance while not complete, is called “durable” resistance because it takes more time to overcome resistance conferred by multiple genes. The nature of resistance in garden plants is rarely detailed by growers or seed sellers. Often we are lucky to see any labeling for resistance. Crops like rose, crape myrtle and snap dragon are often sold as resistant to powdery mildew or rust and in some cases plant breeding programs strive to incorporate disease resistance into their breeding lines but then fail to label the product as disease resistant!
Cultural control is using good horticultural practices to limit the development of disease. Since many plant pathogens require a host to be predisposed, we have the opportunity through good horticulture to avoid the disease development. Planting woody ornamentals at the right depth is a cultural control of Phytophthora collar rots. Appropriate application of water, reduces stress and prevents plants from being predisposed to both root rots and canker diseases. Correct pruning cuts limit the development of decay in trees. Appropriate horticulture as discussed in the Garden Professors page will go far toward cultural control of common garden maladies. Proper plant selection is also a form of cultural control. Choosing plants adapted to the growing area climate, and soils selects plants that are less likely to be predisposed to disease. Poorly adapted plants are more susceptible to pathogens and thus more likely to become diseased.
Biological control is the effect of one organism limiting the development of another thus preventing disease. Classical bio-control is when an exotic pest is introduced and there no natural enemies or parasites to regulate it. The pest/pathogen multiplies rapidly killing or affecting a large plant population. Research in the native range of the host looks for native organisms to control the pest. They are brought to the infestation, released and the pest/disease is brought into control. This works well with insects and the damage they cause. It has also been achieved with exotic plant pathogens. For our native pathogens, there may already be a community of organisms that limit its development. This is especially true for soil-borne pathogens. This is why the GP professors so often recommend fresh wood chips as mulch. Fresh wood chip mulches supply carbon for organisms in soil that interfere with soil-borne pathogens; a kind of mulch-mediated bio control for root diseases.
I find controlling diseases is a lot more difficult than understanding or identifying them. Usually by the time you have observed disease in the garden it is too late to stop its progress. You can take mental notes not to plant that variety again, or prune more diligently etc. but diseases are largely regulated or advantaged by the environment and our good or bad gardening practices. Of course the pathogen has to be present for biotic disease to happen, as we know that organisms don’t spontaneously generate. Disease control starts with identification then research and finally gardening actions that help prevent, limit or eradicate disease propagules.