Opening up a can of roots (or worms as the case may be)

Blog reader Alan Haigh asked if we could start a discussion about tree planting recommendations.  He sent along these guidelines from the Colorado State Master Gardener Program.

While I’m glad to see that the consensus now seems to be that burlap, wire, twine etc. do not belong in the planting hole, there’s still plenty of issues to contest.  Here are just a few that I found on my first read:

1)  Not mulching over the root ball;

2)  Assuming that all B&B trees are “field grown,” which I *know* is incorrect for so very, very many B&B trees;

3)  Not including the root-washing technique for B&B, which is not only research-based but is actively promoted through the International Society for Arboriculture’s workshops (see this posting for instance).  This is the only way to find and correct circling and girdling woody roots, and the easiest way to find the root crown for planting at grade.

Without root washing you’d have to dig through 10″ of clay to find the root crown (the duct tape marks the top of the clay root ball prior to washing)

I’ve written about this topic before.  And many people argue that it would “take too much time” and “be too expensive” to root wash specimens.  But when you read this publication, note that it takes 13 pages to describe how to plant containerized and B&B trees.

It takes 1 page to describe how to plant a bare root tree.

Published by

Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - "The Garden Professors" Facebook group - Books:

30 thoughts on “Opening up a can of roots (or worms as the case may be)”

  1. The root washing is interesting. It would not just reveal circling roots but also place existing roots in the new soil which I suspect could be advantageous. It’s one reason I like transplanting up to 3″ caliber trees bare root. That, and the fact it allows me to move much more root without the heavy soil.

    1. Regarding to an original post I put out there questioning “The Myth of Collapsing Root Balls”— Going to try the root washing, per Linda Chalker Scott, but am scared about it. Don’t understand really why I should be, I guess it’s all a learning experience. Planting now is probably better in the Fall, right? Still need to dig out one tree where I didn’t do anything to the roots before putting it in the ground. I liked an article regarding “Canopy,” a Dave Muffly prepared some 400 trees or something like that for a community project and got all the circling and girdling roots taken care of, practically to the bare roots before planting, so he seemed to know what he was doing. I appreciate advice because I’m on my own kinda strugling with this new information. After watching a woman (Tricia Smyth) From “Essence of the Tree”get her potted Japanese Maple ready to transplant—she washed the heck and pruned the heck out of it.

      I’m undoing a lot of things in my yard garden now, I also need to undo a huge planting bed of shade loving plants from under two trees where I piled tons of soil and amendments to make my fancy bed.
      Taking out plants, repotting plants–geeeezzz. Buzy bee.

  2. Actually, some recent research supports leaving the root ball unmulched. It’s not what I was taught when I started my career as an arborist, but, then neither was most of the things I now do when transplanting trees. Certainly I prefer it to “volcano” mulching. We’ve been seeing the negative effects of that practice for years.

  3. If you could provide more information on the research supporting unmulched root balls, I’d like to see it. In the literature review I did a few years ago mulching is always the better alternative in terms of root growth and improved soil conditions (temperature, water relations, etc.). Now if someone used a foot of compost or sawdust, that would be a problem. But several inches of coarse organic mulch has been significantly better (as reported in the scientific literature) than leaving the soil bare.

  4. Thanks for linking to my blog, Linda! The next post, ‘Root-washed tree revisited’, shows the tree a year later, and compares it to some other oaks, the same size and age planted B&B nearby. Alan’s right, too, about getting those roots into the surrounding soil — without that pesky soil-to-soil interface making it difficult for moisture and roots to penetrate, the roots can simply start growing.

    1. Okay so you have done this to your trees before planting? I’m getting ready to do that..seems radical but going to try. I guess you really don’t hurt the root ball like so many nursery’s say. Give me some tips. I have a feeling it’s going to be messy? Are you saying in your post that you get the tree back to practically bare roots?

  5. Deb, yours was the first that came up when I Googled “ISA” and “bare root.” And thanks for pointing out the update as well.
    I can’t emphasize enough how important it is to get the roots next to the native soil. Taking all of those barriers out of the way is a great start.

    1. I am trying my best to glean information from you Linda. Many thanks, do you have any other links I can read supporting this method of planting I can read?

  6. One addition I’d make to the guidelines would be also to remove circling or girdling roots, as well as secondary rootlets, once the excess soil has been removed from the top of the root ball. In this part of the world it’s almost a given that root flares will be buried, and taking these corrective measures will really go a long way toward letting a tree establish itself in its new home. Not removing those roots can lead to real problems in a few years.

    1. I’m just learning about where the root flare is on Japanese maples. I have a photo I took of one I uncovered from an unplanted tree out in my back yard, not sure if I’m down all the way or not. The only way I can post a pic. is in an email, Can you give me yours so you can tell me? Mine is:

  7. I wish the Col. State Master Gardener info. had gone into the reasons why you would want to leave the root ball un-mulched. It’s certainly counter-intuitive. Nope. I’m gonna mulch it.

  8. Linda I figured you would be all over the issue of mulching over the root ball but my second question is about the the idea of shaping the planting hole as a saucer rather than a cylinder or even a square. The author suggests that having the hole slope sharply upwards is entirely beneficial and I can certainly see potential advantage in steering the roots closer to the surface for more oxygen (and warmer temps). Also you could loosen a much wider diameter hole with less work. However, when I plant trees in very compacted soils I’ve worked under the assumption I could get better anchorage by encouraging deep rooting rather than shallow. Also a cylinder shaped root ball would seem to be less likely to blow over than a saucer shaped one. Blow over is always a risk when planting in wide holes that have been broken into seriously compacted soil.

  9. Alan, roots will grow only where they find oxygen, nutrients and water. Generally that’s the top several inches of soil. Heavily compacted soils don’t have enough oxygen very far down and roots won’t grow there. Mature root systems are shaped like pancakes, not coffee cans, and planting holes should mirror the systems.
    When we’ve done root washed tree installations, we’ve rarely had to stake because soil and water surround the roots and hold the tree in place. A clay root ball planted in a hole is more like a ball-and-socket joint, easily moveable and subject to blowdown.

    1. I like that analogy-thanks Linda! I’m getting more confident all the time! I was worried about that. And didn’t you say that after getting all the soil out of the rootball and pruning etc. That I should or could use this product called Myke (mycorrhize)? And I probably stake it. One gal posted a comment about Japanese Maples being different to other trees accepting this method. Same method applies, right?

  10. As someone who has tried the root washing technique for B&B trees and has lost trees doing it — while having B&B trees survive which were not root washed — I would like to review the research showing that root washing is really helpful. Most of what I’ve seen amounts to isolated testimonials. I am aware of Bonnie Appleton’s work on the subject — this quote comes from her “Caution needs to therefore be exercised when deciding whether to bare root trees at planting,
    since tree species vary in their response to bare rooting, especially relative to time of year or
    growth stage.” I couldn’t agree more. I certainly see some utility for root washing — especially for trees that have been held for too long as B&B (a year or more) — but it’s not something to be freely recommended.

    Quote comes from —

  11. You’re right, Jeff, the published research is pretty thin right now. I’m just beginning a project comparing root washed B&B and containerized maples and pines in the field to look at this over the short and long term. (You can also look at this publication for my earlier work with containerized plants: Chalker-Scott, L. and T. Stout. 2009. Bare-rooting containerized materials: a comparison of installation techniques, pp. 191-204. In: G.W. Watson, L. Costello, B. Scharenbroch and E. Gilman (eds.), The Landscape Below Ground III : Proceedings of an International Workshop on Tree Root Development in Urban Soils. International Society of Arboriculture, The Morton Arboretum, Lisle, IL,)
    Beyond that, there’s a pretty substantial body of anecdotal information from Jim Flott and the City of Spokane, who’ve been doing this for over 20 years, I think. True, it’s not scientific, but when you improve the tree establishment and survival rate from (I think) less than 50% to over 90%, it’s worth noting.
    The tree planting success rate in this part of the country is horrendous. In a relatively new parking strip (which I showcased in January, there were 7 trees planted. Five died within 2 years, one is struggling, and one survived. I would bet my paycheck that if I were to dig the dead ones up you’d find undisturbed clay root balls with virutally no roots extending from them.
    I’d be curious to hear from other arborists who’ve attended ISA’s root-washing workshops and are now following this practice.

  12. Sorry to be slow to respond, I’ve been out of the office over the past few days.

    The recommendations to not mulch over the root ball comes from research work by Dr. Ed Gilman at the University of Florida (his website in tree planting is found at He has presented these finding a couple of time at the International Society of Arboriculture Annual Meetings and folks seem to be on board with it.

    Until his work came out, the GardenNotes advised folks to mulch over the root ball (with the thought that it will help stabilize the soil moisture, reducing surface evaporation. I made the change a couple of years ago to not mulch over the root ball, but rather just over the backfill based on his work. In his research, he found no growth benefit of the mulch over the root ball, but rather just mulching over the backfill and beyond. Depending on the type of mulch used, it can intercept some of the moisture in a rain or irrigation event. If the rain event is minimal (as would be typical of Colorado summer storms), the soil below the mulch could remain dry. I’ve looked at this closely under Colorado conditions and he is correct, we often only moisten the wood chip mulch with little getting into the surface soil with a typical Colorado storm. If your typical summer storms are heavy downpours that soak the soil deeply, it would be totally different situation.

    In his research, non-established recently planted tree pulls all available moisture from the root ball so quickly what surface evaporation from the root ball is insignificant. (I was surprised with the findings, since I generally think of mulch as a way to reduce surface evaporation and save on water needs. But is makes perfect sense when I look carefully at the data. Water for the newly planted tree is coming from the root ball, not the backfill soil.

    The saucer shaped planting hole comes from Principles and Practices of Planting Trees and Shrubs by Gary W. Watson and E.B. Hemelick (I
    SBN 1-881956-18-0). This is the ISA manual on tree planting. Folks have traditionally dug the hole with vertical walls. If the soil is compacted and clayey (and most Colorado soil are clayey with compaction), the roots begin to circle the planting hole when they CAN NOT penetrate the site soil due to low soil oxygen. This leads to trunk girdling roots several years down the road as the trunk gets to a significant size.

    Root spread following the path of low resistance. With the sauce shape, WHEN the roots CAN NOT penetrate the site soil due to compaction (low soil oxygen) the root will follow the texture gradient of the saucer UP and OUT rather than circling the planting hole. As it come up and out, the oxygen levels will increase to a point where the roots can penetrate the compacted site soil and continue outward growth.

    To help the tree anchor, it sits on un-dug soils. IF the bottom of the root ball is slightly curved, firm soil around the base of the root ball to stabilize it before backfilling the hole. With this planting methods, the tree does not rock in loose soil but rather sits firm on the solid bottom. The trick is to rest on the root ball on the solid bottom rather than loose soil in the bottom of the planting hole allowing the tree to rock in the wind.

    David Whiting
    Extension Consumer Horticulture Specialist
    Department of Horticulture & LA
    Colorado State University

  13. Purely anecdotal observations here…
    During the recent winds from Hurricane Irene, we had 16 trees (80 to 100 year old white oaks, chestnut oaks, and red oaks) that either blew down or had to be taken down because they were endangering our house. All that blew over had pancake shaped root systems averaging 12″ to 15″ thick. Those that we removed because of large limbs hanging over the house or that were leaning toward the house but had not blown over, had deeper and more robust root systems. I don’t know if this “proves” anything or not except the fact that our soils are very shallow and have hard, compacted clay at about 12″ depth. Obviously, some of the trees had overcome the compacted layer while others had spread their roots on top of it. It doesn’t say anything at all about root washing prior to planting, but it might give a little hint about the future for trees planted in saucer shaped holes in clay soils. Or then, it may not. Testing seems to be in order to prove or disprove these theories. And it would need to be done in a variety of soils to give satisfactory answers for the diverse soils across the country. Anybody up for a 100 year experiment?

  14. Arborists here in Massachusetts are beginning to rough up the sides of a B&B root ball (after which they cleanly cut the ends of any torn roots), to help make a more hospitable soil-to-soil interface for roots to cross. Those cuts on the larger roots should face down, so that the regenerative root sprouts that come from the end of a cut root will be more apt to grow out and down — with a straight vertical cut, the new root sprouts tend to grow upwards. Putting the tree well just outside the root ball, rather than on top of it, and then watering thoroughly inside the well, also helps water penetrate into that interface and so encourages roots to grow outward.

  15. I do a lot of fall transplanting from my bearing age fruit tree nursery here in southeastern NY. The research David mentioned was by one person and entirely in Florida. Here in Z6 mulch is about much more than slowing evaporation and fall planted trees need to be mulched to insulate the roots when they are in a light potting mix or if snow is not there to protect them they could freeze. I also believe that freeze-thaw can push a root ball out of the soil if it is left uninsulated.

    There is no way I’d run with the research of a single person in a single location and probably a single soil type- especially when all those factors are much different then where I’m doing my planting.

  16. Let’s all get to the root of the source. Root washing works. Yes it is based on a few research studies with Bonnie Appleton, some research on container washing by Chalker-Scott and decades of field use originally in Nebraska before taking it west to Spokane. Most of the trees we planted in the city program were root washed fully or partially. My failures have occurred from correcting root problems found and removing defects during root washing leaving so little of the root system left that chances of survival are slim. On the other hand if we do not fix the root system at the time of planting these problems manifest later and after much investment in the tree.

    I agree more research needs to occur on species phenology for bare root transplanting. The transplant lists available to us now are merely anecdotal developed from tradition and not much research to support categorization of easy, moderate, or difficult to tranplant.

    Also when comparing root washed trees vs. traditional B&B planting it is critical to compare the quality of the root system and how can one do that on a B&B tree if it is not visible. Hard to evaluate as we know all root systems are not created equal particularly what we are receiving from the nursery industry. What is the quality of the root system left after root washing, once all the defects are corrected. If those same defects occur on B&B trees I would expect the trees to survive longer than a root washed tree that had substanial root mitigation to correct problems. What happens down the line to those B&B trees that look fine the first few years–the defects begin to show up.

    I don’t claim 100% survival with root washing but neither can you with traditional B&B or container planting. What I do claim is it is a technique for fixing poor quality root systems. Sad but it is the nature of the products produced currently.

    Also we are moving large diameter (6 inch to 20 inch DBH) trees bareroot–nothing new. It was done that way long before the advent of containers and B&B dug trees. Some have been moved in full leaf without missing a beat in July.

    1. WEll Hello Jim Flott–I just tried to email you via the Community Forestry Consultants to inquire on this very subject and here you are. But this was way back I see 2011, hope you re reading you posts on this website. if not can anyone give me a direct email to you?

      I have two Japanese Maple trees I dearly want to make it, and so I have been gathering data and will soon begin this washing of the B&B tree. (I also have a potted tree I planted previously.. and will have to dig it back up to open up the root ball). I guess being gutsy with the root systems is not a laughing matter since nursery’s in Kansas City tell me to just bury it & that’s it. I really want to understand this and have been enjoying the learning process..

  17. 6 to 20 inch caliber trees moved bare root in July?!!! No wilt or growth lag whatsoever?!!!

    Time for me to start my nursery in sand- just dig up the trees with some kind of power fork or an air or water spade and move them with the roots in a slurry to their new site. Reduce shipping costs by at least 50% and production by about the same (no soil replacement needed).

    If this is doable you’d think the industry would be all over it. If this is doable.

  18. This post is quite disappointing. Rather than being fact based, the information and follow up comments by the writer sound much more like someone with an extreme bias. It does not take 13 pages to describe how to plant a B&B tree, and you can be certain that 13 pages could be written to describe root washing. The comment that there is only a 50% survival rate for planting B&B trees is laughably inaccurate, and far below the standards of this site, as is the evidence that 5 of 7 trees planted in a parking lot died.

    When root washing is addressed there seems to be a common belief that the root flare of all B&B trees are buried by tree nurseries. Certainly I have seen this, but the problem is evident in a small percentage of trees, not the majority.

    If this was my first time reading this blog I wouldn’t be back. I don’t doubt that root washing should be considered, but I have not seen adequate information thus far. Misinformation and stubborn i
    nsistence that “my way is the only way” with implied criticism of all who disagree will not forward this cause.

  19. Dave, I fail to see any stubborn insistence that “my way is the only way” or any implied criticism here- at least up until your blast where you seem to be doing just those things. Relax, we are not discussing life and death issues here for anything but trees. We have two colleagues who disagree about the efficacy of a new method that both believe still needs further study- big deal. Why not just point out statements that you feel are inaccurate?- all intentions here are positive. I agree that the rates of mortality for trees I see planted produced by the nursery industry are not bad and that there may be some exaggeration of the percentage of commercial nursery stock that is planted too deep or kept in pots too long. I would like to see some serious data on this to back some of what I’m hearing. That might be a nice research project if it hasn’t already been done.

  20. It would be really interesting to plot on a map of North America where people are encountering too-deep root balls or overly constricted containerized roots, and where they are not encountering those problems. Here in Massachusetts I see a significant percentage of woody plants that require root remediation before planting. The thing is, rooting problems may not manifest as problems until several years after a guarantee period has passed; it’s only when a plant dies and someone digs it up and does a little forensic work on it that the circling/girdling/crossing/secondary roots become visible. Elsewhere, this issue may not be an issue. Here, it is, and it’s causing problems throughout the designed landscapes of the state.

    Moving plants bare-root is a great way to go in many instances. If you want to move a large mature tree with minimal tree stress, air tools can make that possible — provided that the movers know how to do it and the tree species is one that permits it. Tender-barked trees may present problems (magnolias, cherries), while trees with fibrous roots can do very well (Japanese maples tend to be tough as nails for instance). The thing is, no one has yet done controlled by-species studies of what trees move best bare-root. It seems that a hybrid move — blowing off the outer third of the root mass and leaving a large slug of soil and roots directly under the tree, rather than polishing the roots clean) gives the best results over the widest range of species. As for nursery production, bare-root still is a great way to plant a tree, but as Alan points out, bare-rooting large quantities of larger trees may not be cost-effective for the growers. The techniques that may be best for the plants may not be what’s best for a grower’s most immediate bottom line (which, to circle back to my first point, is why we wind up with buried root flares and circling roots — production techniques are often set up for speed, rather than for the long-term health of a plant.)

    Interesting can of worms/discussion, though.

  21. Deb brings up really good points. When I researched the Shigo method in college I found that there are so many variables in what makes a pruning cut a good one: type of tree, time of year, etc. These variables sometimes supported the Shigo method and interestingly, sometimes they did not. With regard to the current discussion, Prof. Gilman has great research but my north Georgia red clay, zone 7b is not the same situation as Gainesville, Florida. Besides zone (hardiness) there are obviously factors with regard to soil, heat index, rainfall and growing conditions via the grower. This is why I love horticulture: it really is a science based art, as these garden professors themselves have said on previous posts as I recall.

  22. Because I have a small nursery of only fruit trees, I certainly get to see the variability of response to BR transplanting, albeit a limited number of species. Here’s some observations I’ve made transplanting thousands of trees over the years- much of it bare root. For those not interested in the specifics I’ll just summarize by saying that species response does vary greatly, IME, and anyone interested in details can continue reading.

    Pear trees are the most sluggish to recover from root disturbance and suffer so much that I’ve stopped sizing them up and then digging them up BR to put in containers or field bags as I do with other species. I put them in grow bags from the first, when I receive them as BR whips.

    Incidentally, most nurseries that produce pear trees for commercial fruit production reject Carl Whitcomb’s conclusion that severely pruning back trees is never helpful towards their transplant recovery and some will not guarantee pear trees that haven’t been severely cut back when planted. I believe this might be an example where research is sometimes only relavent to the specific species or even cultivar studied.

    No matter how carefully I dig pears- especially large trees, bare root, I suffer a high mortality rates and consistent growth set back. Pears moved with a large ball of earth do much better.

    Japanese plums are on the opposite side of this equation, recovering so well from bare root transplanting that they usually get vigorous growth their first season of being moved. Prunus species in general seem to move particularly well bare root although peach roots are very brittle, so great care must be taken with them to avoid snapping roots. Contrary to what was noted by Deb, the kinds of cherries I move transplant very well bare root- including larger trees. I don’t see why ornamental varieties would be more difficult as they have similar looking roots.

    As a general rule, fibrous rooted species transplant bare root best (or just with the soil that sticks to the roots).

    I suspect that using root washing with pear trees would be extremely counter productive when transplanting as would be the case for species with similar non-fibrous root systems.

    A last point I’d like to make is that not only is the type of plant an issue but also the maturity, as plants that have begun producing flowers, fruit and/or seeds are less amenable to the stress of transplanting. Significant energy is being syphoned towards fruit and/or flower production at the expense of roots.

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