Problems with Planting Trees

 

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.

An old planting detail from “a book of trees” . Several myths here: rocks at the bottom of the hole, amended hole, nursery stake still there when it does not need to be, etc.

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 do not function well in most landscapes and lead to the development of landscape trash. They can also create root defects

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.

A “lollipop” Tree.  Note the very skinny un-tapered stem, lack of temporary lateral branches and retention of the nursery stake–all bad…. Also note the tree snorkel lurking to the left. Kudos for keeping turf away but not far enough away.

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.

Providing a No Turf Zone around trees will aid in their establishment

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.

Aeration/Irrigation snorkel tubes do not help trees and result in landscape pollution. Note the original nursery stake still in place and the supportive stakes should have been removed long ago. Mulch needs to be replenished.

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.

Published by

Jim Downer

Dr. Downer has 34 years of experience as a horticulture and plant pathology Advisor with the University of California Cooperative Extension in Ventura County. Dr. Downer’s academic training is from California Polytechnic Univ., Pomona, (BSc. horticulture & botany, 1981; MSc. Biology, 1983;. In 1998 he earned a Ph.D. in plant pathology, from University of California, Riverside. Dr. Downer’s research is focused on mulch, soil microbiology and disease suppression in mulched soils, diseases of shade trees and cultural practices to maintain landscape plants. Dr. Downer is a member of the American Society of Horticultural Science, the American Phytopathological Society, The International Soc. of Arboriculture, and the Western Chapter of the ISA, and the International Society for Horticultural Science. Dr. Downer is an Adjunct professor at California Polytechnic University in Pomona. Dr. Downer serves on the Board of the John Britton Fund for tree Research as the chair of the research advisory committee, and currently chairs the regional conference committee for WCISA. Dr. Downer has a love of shade trees, Shinrin roku (forest bathing/walking) tree work, wood working, horses, gardening, horticulture and the study of plants and their biology.

27 thoughts on “Problems with Planting Trees”

  1. Ann Arbor has had an aggressive street tree planting program the last several years. At first they hired a contractor to water the trees and trees were planted with an odd green bag around the bottom of the tree. I found these online and they claim to be a slow drip water delivery system. These always looked suspect to me and more recently they are simply asking residents to water new trees.

  2. How does this advice change when you are planting a replacement ahead of time? I have 2 Arizona Ashes that are almost 40 years old and I’ve been told I need to get a replacement (not another AA) in the ground now. I’ve been told I should plant 10 feet away in order to preserve the shady canopy in my Austin,, TX yard.

    1. In Austin, planting season is ending now. Our mild winters and hot summers make fall planting best. It’s probably a good idea to have an arborist prune the ashes back from the new tree, both to increase light and reduce the chance of a branch breaking and crushing the new tree. Otherwise, plant it the same as any other.

  3. “Plant the youngest tree you can.” I had to smile when I read this because it’s the first time I’ve ever read such advice as my father used to give in the 1950s
    . . . his argument was that a young tree will be the same size as an older one within a few years . . . so why go to the trouble and expense of putting in a larger one?

  4. Do you have a citation to support digging a hole only slightly larger than the root ball? The International Society of Arboriculture still recommends digging 3x the width. If this is verifiably unnecessary or detrimental, I’d like to see them update their recent.

      1. 3 times the width is ridiculous whether that is the ANSI standard or not. Why? It is impractical. OK, it is fine for a smaller tree but we recently moved a tree with a 70 inch root ball. 6 feet. The standard would say to dig a hole 18 feet wide. Really? I have found very good small tree establishment when breaking up soil in a wide area in chunks, maintaining soil structure, but that is admittedly not replicated, peer reviewed research.

  5. What do you recommend if you need to add more soil to the hole? For example, my soil has a lot of rocks in it, and if I don’t put them back in, I need to put *something* in. Should I just find an empty spot somewhere in my yard and scrape up some extra topsoil?

  6. Wow! What a refreshing article. I’m new to both your blog and to your FB website. As a MG for only three years, I need to live till I’m 100 to just begin learning all I want to know. I’ve seen many methods to plant a tree that are so complicated, and it’s great to see one that makes sense. Howard Garret in the Dallas area was the first I knew to advocate no staking of trees. I have to admit I’ve been guilty of adding “enriched” soil to a tree planting hole. I’m reformed now, though. I’m presently shopping for a paw paw tree (native to my area of Missouri) that I’ll be planting in an open section of the woods around our house; your article came just in time.

  7. “Dig the hole for your tree so that the roots are very slightly above the grade. Do not double dig!”

    Wish I had found your site before planting 2 cherries and 1 plum around my yard two weeks ago because I made many rookie mistakes… First off I dug the hole the depth of their containers, approx 14″, added bagged topsoil to make up for the removed stuff; then they were placed so that the graft was approx 2″ above the soil, instead of focusing on the root collar; I turned to roots so that they fit in the hole, and put some rocks at the bottom of the hole for drainage in the compacted soil. OH there is more but I am going to end this with a question…If I remove the trees, compact the origional soil into the hole until i get the depth right for the collar, should I use some of the bagged topsoil to finish off the planting? My concern with using the origional soil is that it might leave a void directly under the tree where I cannot pat the soil to contact hair like roots.

    1. If you dig up and replant, don’t compact the soil. Dig a new hole adjacent to the old one, dig it to the appropriate depth and wide enough for the roots, add soil and water until you have standing water (meaning air pockets are gone). The water will drain through the soil, retaining pore space for oxygen. Use the bagged soil on top as I’m guessing it’s NOT actually soil but simply potting media, which contains no soil but is a good source of organic material. Make sure you mulch well with a coarse woody mulch (like arborist wood chips).

  8. There should probably be clarification on removing all the soil and washing the roots before planting. If this is done when the tree is out in full leaf, you will soon have a dead tree. The roots will be too disturbed to support all the leaf growth.
    You would have from mid April when frost is out of the ground to about the end of May to get all the trees in. Forget fall planting, trees have to be dormant which doesn’t happen until late October. Then take into consideration that many trees cannot be transplanted in the fall or they won’t survive
    If nurseries could root prune their trees before potting or lining out to grow for caliper, please expect to pay more for the tree.
    Architects and city planners all spec 60mm or 2.5 in caliper for street tree planting. I agree that a smaller tree does better but we live in a very impatient society that doesn’t want to wait the few extra years.
    Also, in Ontario, Canada, contractors are expected to maintain and warrantee a newly planted tree for 2 years from planting date. Plan to babysit the tree for 2 years to make sure it it watered, not climbed on, no insect or rodent gets to it , oh…. bid against each other for the lowest price possible that you almost make no money.

    In a perfect world, I can agree with most of what is written in this article, but we don’t live in that world

    My 2 cents…

  9. Hope I’m not too late to these comments/questions. A group is having quite a discussion about a tree and grade issue. There is a need to raise the grade in an area. There is a mature tree that can’t be moved in the area where the grade needs to be raised. It was proposed that they raise the grade gradually several inches over a course of time (say, 3″ per year) allowing the tree roots to “rise” to new grade levels. If this is done, you can’t have a deep ring around the trunk…would you add the soil up to the trunk as well so it can adjust? Or, what is the best method to preserve a tree when raising a grade? If using mulch, could you raise the grade 6″ per year? We can’t seem to find references for this situation.

Leave a Reply to Yvonne Cancel reply