Advancing the science of gardening and other stuff since 2009
Why root washing is important – an illustrated cautionary tale
I’ve promoted root washing of containerized and B&B trees and shrubs for a few decades now. The experimental science is slowly coming along – it can take several years to determine if the practice is more successful in terms of plant survival than leaving the rootball intact. But we know how soils function in terms of water, air and root movement, and we understand woody plant physiology. So it’s pretty easy to predict what will happen when trees, whose roots are held captive in layers of stuff, are then planted, intact, into the landscape.
Early in spring 2021 I purchased a couple of Japanese maples to frame our garage. As always, I root washed these specimens. Here’s a play by play of what we did, and what we found.
After more cleaning and untangling, we have a root system ready for planting. Well, almost.
If you are still wondering why this is a cautionary tale, consider what would have happened if the rootball was planted intact:
The root flare would have been buried below grade.
There would be multiple layers of stuff between the roots and the native soil (i.e., clay, burlap, and media).
The twine circled around the trunk would girdle it eventually.
The poor structural roots would not create a stable support system.
Now, one can argue all they like that there isn’t a robust body of scientific literature to recommend this practice – and there isn’t, yet. But leaving rootballs intact creates textural discontinuities between the roots and the native soil, and poorly structured woody roots are not going to correct themselves. So why not embrace a practice that removes both the soil and root problems?
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 - www.facebook.com/TheGardenProfessors
"The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors
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34 thoughts on “Why root washing is important – an illustrated cautionary tale”
Are you saying not to replant at the blue line? How deep should we plant? Thanks for clarifying.
Yes, the blue line is ABOVE the root flare. It needs to be planted so the root flare is at ground level.
What is the benefit of planting the root flare at ground level, and what is the negative effect of not planting at ground level?
The easiest thing to do is to search the archives of the blog to find posts about this. Go to the search box on the blog menu and search for “flare.”
I recommend the Blog post titled “Planting with a Flare” for a better understanding of the reasons why planting at ground level can be so important.
Thanks for this article. Unfortunately, most trees are still planted too deep, mainly because they come that way from the nursery. Your method allows the correct depth to be easily determined. I will follow your lead in the future.
It’s clear why root washing would be promoted for containerized trees. Leaving that root ball as it comes out of the pot is pretty much always a disaster. What I don’t understand is why you are proposing the same treatment for field-grown B&B trees? I always go to the nursery and tag the trees myself so I can make a good selection, locating first order roots, staying away from trees that have been headed back, etc. I also note if, as a result of nursery practices, the trunk flare is buried. Any and all such problems are then addressed in a specification that I provide to the nursery such as the requirement that all excess soil above the trunk flare be removed prior to digging so that soil is at the correct grade in relation to the flare. That way I have a tree that is properly situated in relation to the resulting ball and the tree gets the maximum amount of roots the tree spade can provide and according to ANSI Standards. I don’t think root washing should be recommended if proper procedures are in place. In addition, we know from bare root research that not every tree can be produced using bare root protocols which might also have relevance to root washing practices.
“Field grown” doesn’t mean the tree was grown from seed in the field. All of the trees I’ve purchased as “field grown” were obviously planted from containers and then finished in the field. Furthermore, if you don’t take off the clay, or find the root flare, you will have problems as outlined in this post as well as several others I’ve posted in this blog over the years.
Regardless of what ANSI standards say, they cannot change the science of soil functionality. And there is no theoretical or practical science to support the notion that root washing would work for some species but not others. What would be the physiological reason for this?
Thanks for the illustrations! It seems that all the “standard” advice about planting containerized trees is bound to fail these days because it assumes the trees are planted corrected in their pots. “Don’t break up the root ball, plant at the same level, dig a huge hole and amend it heavily”….well, good luck with that. Your methods are working for me; it’s essentially creating a bare root plant out of a containerized one. The few trees or shrubs that I have just planted pretty much “straight from the bucket” have done very poorly or even died, whereas anything bare-root is growing nicely. Planting to the root flare, not amending the soil and “mudding in” have been very valuable techniques. As is not staking the trees.
Growers pull a lot of tricks and if you don’t investigate the root ball, you’ll never know. I’ve seen where they like to put up a very small tree in a bigger pot — no roots at all in most of the soil. They bury the root flare under five inches of mulch, dirt and fertilizer. They water with drip irrigation in one spot on the side of the pot, and that’s where all the roots grow, including roots that went to the bottom of the pot, turned around and grew back up to the top! It’s stressful to buy an expensive potted tree, pull it out of the pot and then have to cut away half the roots.
But thanks again for your practical advice. The trees want to grow, we just need to get out of their way….
I’m so thrilled to read this! I have planted dozens of trees this way over the last several decades. It works! I struggled with doing my planting this way because I knew that I was going against the “standard advice” of the time, but I always have good results with bare rooting the potted specimens before planting them. Occasionally I have root washed a tree from the nursery and realized it was not worth the investment of planting that particular specimen.
Thank you so much for the work you do and communicating it so clearly!
So, if you previously planted a tree (Spring 2020 and 2021), without root washing, when should I dig them up to redo? Both are apple trees and leaves are just coming off. One was severely damaged by hail this summer. Manitoba Canada.
Do the wiggle test to find out. Search this blog for “wiggle test.”
Coincidentally, I’ve been watching your series available on Amazon Prime. I’ve done a lot of fall planting and have practiced this method now. I also dug up some trees planted earlier this year and made sure the roots were treated correctly. Previously, I would simply scour the root ball minimally and plant but never removed all the organic matter that comes from nurseries.
I have established junipers and other leafy shrubs, that I would like to dig up and move to another location in my yard. Would you also apply root washing in those situations too?
Mike, it depends on if they are doing well. If you dig them up and they have a vigorous root system, you don’t need to do anything other than move them. If they come up easily and don’t seem well established, I would wash, correct, and replant.
Thanks for the response. They are well establishes, but would it harm them if I still went ahead with the root washing in order to reduce the moving weight?
Oh sure, shake off or brush off extra soil. I would not wash in situ, as you will make a muddy mess of your site soil and it will become compacted. If you need to wash, put it in a tub.
Thanks. Much appreciated. I will do that!
Just chiming in to point out the potted plants are Cordyline and not Phormium
Interesting! They were labeled otherwise, and I am not a taxonomist by any stretch. But that explains why they get so tall – and don’t die off in the winter! Thanks for the correction.
Thank you. Interesting words.
I have done the same thing for years after losing many trees and shrubs due to a root bound and hardened “root ball” that would not allow moisture and nutrients to penetrate it once planted. I have consistent success with this method! Thanks for publishing the method and logic behind it.
Extraordinairyily helpful! Sending it out to both my Garden clubs. Not too sure if I understand ‘Knee Roots’ though; cut where they go 90 deg. down,, but in the photo it looks as if they angle suddenly to the left ??
Yes, they can go any direction. It’s what happens when a young root hits the edge of a container and is left in said container for months after.
I came across another good reason for root washing as I finally got around to planting the nursery plants I’d accumulated over the summer. I started with what looked like a multi-stemmed camellia planted too deep, and found three distinct plants! Same thing happened with an Oregon grape (four plants, one was not even the same kind of Oregon grape) and an evergreen huckleberry (two plants). Apparently nurseries may not be bothering to cull their seedlings.
I was a bit stumped as I bare-rooted a Western azalea because it looked like several plants growing tightly together. I ended up leaving them all together. How can a gardener tell whether we’re dealing with one multi-stemmed or clumping plant, versus multiple plants that need to be separated?
You can’t tell until you get it unpotted. It’s best to separate them, as otherwise they compete with each other and nothing does well.
Look at it as a bonus.
(See a related post on this blog – five little lavenders.)
Hello ! We have to remember that horticulture is big business . And big business is out to make big money. The growers rarely care or are knowledgeable about absolute appropriate care for optimum growth. They care about fast production, to the market, and “nice looking plant “for the gardeners, who in turn can investigate and perform all the steps we’ve seen here -if at all informed , or interested–and incidentally, I do this to tropicals oh so often! And do any of us suspect for a minute, that landscapers take the time , or even care about this ? I was a contractor for almost 30 years , and am well trained in horticulture and landscaping prior, and KNOW these things. But never could I afford the processes involved to do this to every plant we installed. That is not to say I am always watching and aware of potential problems. So , these procedures are for the individuals totally interested , and having so much time to do this. So for correct procedures to REALLY have an effect on plant growth , it as to start from the very beginning . A very good place to start !! Cheers ! Allan , Bsc., O.D.H.
Hi I have a magnolia tree, after poor flowering erratically I’ve been told I’ve planted it too deeply , I planted it in the container it came in from the nursery, so most likely it was done incorrectly. Its 10 years old now, still a very small tree, could I dig it up in the fall when it’s dormant and root wash it or will it damage it.
Sure, if it is still alive it’s still able to regenerate a decent root system. I would certainly try.
Thank you I will try this in the fall when it’s dormant.
I wonder about subjecting Arbutus menziesii to root washing treatment. It is notorious for hating transplanting anyway. Would there be woody plants with roots so sensitive to damage that this treatment would be detrimental?
There’s not really much difference among woody plants physiologically (until you get into ecosystems like wetlands or deserts). Arbutus is no more difficult to root wash than anything else – I’ve done them myself. The reason they have a reputation for being difficult to transplant is that many people, especially restoration ecologists, don’t plant them correctly.
I was told by a grower not to Nate root plant while a tree has leafed ou? Only do with dormant trees?
If you use the search box and look for “root wash” or “bare root” you will find other posts that discuss timing (like this one: https://gardenprofessors.com/set-your-roots-free-on-this-independence-day-week/_). Bottom line: you can do this any time of the year, but the short term result will be leaves that are stressed or die. They will be replaced, especially if you are vigilant about providing consistent irrigation and a thick layer of arborist chip mulch. If you have to do this in the growing season (which is not the ideal time), be sure to do the work in a shaded, cool, and moist environment. Keep the root ball in water at all times that you aren’t actively pruning.