Category: Uncategorized

If you follow national news, you may have noticed that Sudden Oak Death disease caused by Phytophthora ramorum has been found again in a new state and has escaped into retail commerce and thus into gardens. This is news because the disease is a killer of rhododendron, oak, camellia and many other ornamental plants. Yesterday I was measuring trees in a research plot here in California and I found that one of my subjects had turned brown and lost all its leaves. On checking, I discovered a Phytophthora collar rot was the cause of the symptoms. Phytophthora diseases kill woody plants, often our cherished specimen plantings. This blog post is to introduce you to Phytophthora collar rots, their diagnosis and treatment.

Phytophthora means plant destroyer in Latin. It is the “deathstar” of plant destroyers and once it has infected, death is the usual outcome. All Phytophthoras are Oomycetes. These are organisms that form an Oospore. Oospores are usually produced when two strains of Phytophthora join and the sexual organs form resulting in this spore. It is thick walled and can live for years in soil without a host. Phytophthora used to be considered a fungus but this was changed some years back to put all Oomycetes in groups that are more closely allied with brown algae. Phytophthoras are not in the kingdom fungi but rather the SAR supergroup of organisms. One main difference between these microbes and fungi is that Phytophthora has cellulose in its cell walls just as plants do. There are hundreds of species of Phytophthora, most affect flowering plants especially woody plants. Very few affect grasses and monocots. There are some that affect palms and others, vegetables and herbacious plants. The late blight fungus Phytophthora infestans caused the Irish Potato famine that resulted in millions of deaths (of people and potatoes) and migration (of people not potatoes) to the United States to avoid starving further.  caused the famous Jarrah (a Eucalyptus spp.) die off in Australia, one of the largest known forest epiphytotics. Phytophthora species occur worldwide and affect plants in almost every garden.

Why are Phytophthoras so successful and how do they get into gardens? I think the answer is that they are cryptic. You can not see any of the spore stages, even with a microscope. There is no “mold-like” growth of the pathogen that you can see either in soils or on the plant. This is because the organism lives inside plant tissues and is very reduced in soils where is survives as spores. Unlike many fungi, you can’t see the mycelium of most Phytophthora species. In plants, Phytophthora usually grows in the vascular cambium of roots or stems and kills those tissues. Plants react to Phytophthora by producing phenols and other phytochemicals turning tissues brown. Brown roots or spreading brown cankers on the main stem are common. When Phytophthora kills the tissues on the main stem this often causes a basal stem canker near the soil line. Usually the plant collapses rapidly with all the leaves turning brown or falling from the plant suddenly. Sometimes basal cankers are associated with deeply planted trees and shrubs or where soil has been added over the root collar. Since basal cankers are under the bark they may not be visible while active and need to be revealed with a knife to expose the brown tissue.

Phytophthora diseases are increased by excess water in soil or on plants. Overly wet situations are predisposing to these diseases if the pathogen is present. Other conditions like reduced oxygen in the rootzone (from compaction), increased salts in soil, very dry conditions followed by very wet circumstances all promote Phytophthora. There are also some groups of plants that seem to be very susceptible—these include: rhododendron, camelia, oaks, cyclamen, most plants in the Ericaceae (madrone, manzanita, blueberry etc.), cedars, pines, and the list goes on. It is hard to avoid susceptible plants because there are so many of them.

Phytophthora species are not native everywhere but have been distributed far and wide by people. Nurseries are prime disseminators of Phytophthora infested plants. Fungicides “subdue” the pathogen but do not eradicate it. So a plant can look healthy while still being infested with Phytophthora. When the fungicide wears off, the plant may become sick if conditions are right for the Phytophthora to grow. Another reason why this type of pathogen is so successful is that a plant can have 50-75% of its roots killed before symptoms begin to show on above ground plant parts. Wilt and collapse only occur very late in the progress of the disease. Because of this, it is important to inspect plants before bringing them home. Never purchase a plant with brown feeder roots, or this could be the starting point for Phytophthora in your garden.

If you are an avid gardener who likes to try new plants all the time, then your future encounter with Phytophthora is likely inevitable. You can do things to limit its development.

-Plant on berms or mounds while avoiding planting in low or poorly drained places
-Use wood chip mulches from freshly chopped tree parts
-Add gypsum to soils as part of your mulching protocol
-If you irrigate your garden allow drying out periods between irrigations
-Plant “high” so that the root crown is clearly exposed
-Do not volcano mulch or cover the root crown with anything at all
-Avoid planting woody perennials in turfgrasses or lawns

Fresh wood chips are often broken down by fungi that release cellulase, this enzyme is toxic to all Phytophthora’s, and the reason why FRESH mulches are so important to create soils with cellulytic enzymes that destroy this pathogen. As gypsum dissolves it provides a slow release source of calcium ions which are also toxic to the swimming spores of Phytophthora. While fungicides can also help limit Phytophthora development, the cultural practices listed above will be just as important in preventing and limiting root and crown rot disease in your garden.

About this time last year I posted photos of the installation of my new pollinator gardens (all perennials). As you can tell from the photos below, all of these plants have not only survived but thrived with their midsummer rootwashing.

The only ones that didn’t make it were the six Lavandula stoechas ‘Bandera Purple’ (see above). They did fine through the summer and well into winter. But with our surprise snowstorm in February (along with a 20-degree temperature drop in one night – from 33 to 14F), all but one of these marginally hardy plants (USDA zones 7-10) gave up the ghost. I won’t make that mistake again. But I will continue to root wash ALL of my perennials before I plant.

And since it’s Independence Day here in the US, I thought I’d continue with the “free your roots” theme and discuss the medieval torture system that passes for recommended B&B tree installation practices. I’m talking about the burlap, the twine, and the wire baskets that are left on the root ball and cunningly hidden underground to do their damage over the years.

There is a great deal of disagreement about what to do with all the foreign material that’s used to keep tree root balls intact during shipment. To be clear, that is the ONLY thing they are intended to do. There is no research that shows leaving them on benefits the tree at all. The reason they are left on is because it’s more economically feasible for the installation company to do it this way. Personally I think that’s a pretty crappy reason, particularly when you are looking at trees that can cost hundreds or thousands of dollars.

Most studies that have addressed the issue have been short term: two or three years, rarely longer. Irreversible damage to roots can take years to develop. It’s useful, therefore, to look at the landscape evidence to see what happens with all these barriers to root growth and establishment.

Arborist and landscape designer Lyle Collins recently excavated the remains of trees that had been installed in 1991. The trees had died years ago and certainly hadn’t grown much as evidenced by their trunk size.

But while the trees didn’t survive, the burlap, wire basket, and webbing were all still there almost 30 years later.

The clay rootballs are nearly intact as well. That’s not what you want to see. Roots must establish outside the rootball into the native soil, or they won’t survive.

Eventually I’m convinced long-term research will show the folly of leaving foreign materials on the rootballs of B&B trees. In the meantime, I’ll continue to plant trees in a way that ensures their roots are in contact with the native soil and free from any unnatural barriers to growth.

The dog days of summer are here and as we approach the longest day of the year (summer solstice is June 21st), we are also feeling the advance of high summer temperatures. Long days mean more evapotranspiration and water withdrawal from the soil. During these long days, plants photosynthesize more, grow more, and use the most water during the month of June.  In fact evapotranspiration looks generally looks like a bell shaped curve when plotted by month (figure 1).  Soils dry quickly and irrigation or rainfall may not keep

up with plant demands for water. This can bring some very real stress to garden plants and turfgrasses.  If you live in a place that does not receive summer rainfall you will certainly need to increase irrigation to reflect day length at this time of year.

Transpiration is water loss through leaves and is not  part of photosynthesis, but it is critical to cool the plant. As soils dry out, the level of abscisic acid produced in roots increases and translocates to leaves resulting in the closing of the pores called stomates. Closed stomata reduces transpiration, but only at a steep cost to the plant. That cost is heat build up. Since this is also the time of the hottest weather it is not long before leaf temperatures rise to lethal levels and sunburn results. Sunburn is always seen as damage in the middle of the leaf because that is the hardest spot to dissipate the heat. The edges that lose heat rapidly are usu

ally not burnt (Figure 2).

Short of applying water properly, what else can be done?   Mulches are a great way to avert drought stress since they reduce water loss from the soil surface. The effect is greatest where sun hits the soil. So in new gardens or gardens without a lot of shade, mulches are essential during hot weather to reduce plant stress. Wood chip mulches are particularly helpful in that wood does not reflect, hold or emit heat as much as soil, so it protects adjacent plant surfaces from heat.

How about water absorbing polymers or hydrogels? While much of the allure of these “water crystals” has worn off, it is still good to remind that polymers don’t change evapotranspiration rates of plants so even if they did all the things they claim to, they won’t get plants through a hot summer any better than if they were not present in the soil.

With the longest days come warming soil temperatures.  Hot soil can affect plants especially perennials.  Ground that is not mulched will radiate infrared onto plant surfaces, this can increase stress. This is yet another reason to employ wood chip mulches around perennials.

So when it is particularly hot and dry how can we get plants through this stressful time? Running sprinklers (where practical) will increase humidity and if soils are dry reduce stress (Figure 3).  For annual plants, some shade is often helpful. Applying shade cloth to sensitive or newly planted/emerged plants can cut stress dramatically.  As plants establish, the shade can be gradually removed.  Keep irrigation even so moisture is always there to maintain transpiration — this  is essential during warm weather and long days. For perennial plants there is not much to be done. While pruning will reduce the amount of surfaces that lose water, pruning (thinning) will also lead to temperature increases in the plant canopy since the evaporative surface area of the plant is decreased. So while soil water is saved, canopy temperatures may rise, this may be a poor trade off in the hottest months of the year.  Over-pruning opens plants up for sunburn on stems which can lead to fungal canker infections by pathogens like Botryosphaeria. This is very common in Apples.

Another treatment you may have heard claims for are anti-transpirants. These are products that are sprayed on plants to create a film that will cut water loss from leaves. Taken from a recent Amazon search I found the following product description recently… “Product is a water-based, semi-permeable polymer coating that can minimize the damages from climate related stresses, such as frost and freeze, heat stress and sunburn, drying winds, and transplant shock. Applied as a foliar spray, Product provides a unique non-toxic, biodegradable, elastic membrane over the plant surface to reduce moisture loss and insulate the plant.” While there may be an application (such as freeze protection) that makes sense for this kind of product somewhere, I don’t see it in your garden during hot weather. Cutting transpiration (“reducing moisture loss”) will increase the heat on leaves, so one of the common side effects of using these products is hot weather is damage or phytotoxicity.  Like polymers the fad is faded.

Sometimes the dog days of summer bring insurmountable challenges. In early summer of 2018 in California, temperatures reached record levels of 115-120. Even in irrigated situations plants were damaged, short of providing immediate shade, there was nothing to be done and many plants were injured, even native plants are not adapted to such high temperatures. If these conditions occur in your garden, you may not be able to limit damage, but there are considerations for after care when this kind of blitz occurs. Don’t prune anything immediately, let the leaves fall and buds form because stems may be intact. Prune away injured plant parts after regrowth begins. If injury is severe, cut back on irrigation. Injured plants don’t require as much water because there is less functional  leaf area. This is why root root rot often follows this sort of severe injury. The summer solstice is here—I can already feel the shortening days of fall some distance away.

Reference

Costello, L.R., E.J. Perry, N. P. Matheny, M.J. Henry, and P.M. Geisel.  2014.  Abiotic disorders of Landscape Plants.  University of California Division of Agriculture and Natural Resources Publication #3420.

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.

References

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.

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.