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.

Maple newly purchased from nursery.

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.

Container removed, exposing fine roots. Some of the media has fallen away and is at the bottom of the wheelbarrow.
Since we can’t see the root flare, we mark the point at which the trunk and soil meet.
As we remove the container media, we find burlap and twine. And under that, a clay root ball. There is a root crown somewhere…
Some beating on the clay rootball helps create some cracks where water can then help with the process.
Into a nice soaky bath to loosen up that clay. The longer it sits, the more clay will slough off.
We speed the process along with a directional spray of water.
Jim gets his fingers into the wet clay to pry it away from the roots. Still no root crown, but you can see the Sharpie line on the trunk a couple inches above the clay.
Eureka! A root flare several inches below the original media level.

After more cleaning and untangling, we have a root system ready for planting. Well, almost.

We have roots, but we still have some problems.
It’s got some pretty crappy roots (from not being potted up properly at the nursery), and the remanent of a stake next to the trunk (about 4 o’clock). But there is a nice structural root to the left, with healthy fibrous branches.
“Knee roots” have to go (I call them “knee roots” because they are at 90 degree angles). They have poor structure and will only continue that downward growth pattern, rather than growing outwards. The easiest thing to do is sever them when they turn downward at 90 degrees – don’t worry about removing them if they are too tightly entwined. New root growth at the cut will be directed outwards.
We neglected to get “beauty shots” of our maples through the summer, but you can see one of them to the left of the New Zealand flax plant in the pot. Both maples established their root systems quickly and grew vigorously throughout the summer.
Now in late October, the maples are turning color. Note the distance between the trees and the garage – this ensures that we will have little branch/building conflict as the trees grow in height and spread.
Here’s one of our beauties getting ready to shut down for the winter. They thrived throughout the summer, even when we reached record high temperatures. We look forward to their continued success in years to come.

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?

Caveat emptor!

What’s wrong with my tree? You won’t find the answer in a book.

This tree suffers chronic drought stress every summer. Why?

It’s the middle of summer, and maybe you’re wondering what’s wrong with your landscape tree (or shrub) that just doesn’t seem to be putting on the growth that you’d expect this time of year. Before you take any “corrective” action, let’s figure out what the problem might be. Here’s a short checklist that we will start with. (NOTE: This is just a start. You can go so many different directions once you have some specific concerns to explore.)

Do you have one of these? If not, you can’t adequately diagnose problems.
  1. Soil information. Have you had a soil test done in the last few years? If so, are there any nutrient toxicities indicated? Has the soil been significantly disturbed or modified in the last several years? Have you recently added any chemicals (fertilizers and pesticides, organic or otherwise) or amendments?
  2. Plant information. When was the plant installed? Was it in a container or in a burlapped rootball? If so, were all materials removed from the roots by root washing before planting?
  3. Planting information. Did you amend the soil (i.e., add anything to the backfill) prior to planting? If so, what did you add? Did you mulch it afterwards? If so, what is your mulch material? Did you ensure that your plant was set at grade in the landscape? (“Grade” means that the root flare is at the soil surface.) Did you water it in well and avoid compacting the soil? Are new plantings adequately irrigated during their first year in the landscape?
  4. Environmental information. Have there been unusual weather events between time of planting and now? Is there sufficient irrigation and drainage?
  5. Symptoms. What are you seeing that concerns you?
Intact clay rootball after 28 years (and yes, the tree died long before this photo was taken).

At least 95% of the landscape failure cases I’ve diagnosed over the last 20 years can be traced back to improper planting methods. You simply cannot pull a woody plant out of a pot and stick it in a hole. There are three major factors at play here to consider when rootballs are planted intact:

Think that this root system can straighten itself out? Think again.
  1. The textural and structural differences between the soilless media around containerized roots (or the clay in a B&B rootball) and the soil in the landscape are significant enough that they will impair water, air, and root movement across the interface. This means roots have a difficult time establishing outside the planting hole.
  2. Any structural flaws in the root system created during improper potting-up at the production nursery, such as circling or J-hooked roots, are undetected and uncorrected. And these woody roots will stay in a death spiral after planting.
  3. If you cannot see the root flare of your plant, then you cannot plant at grade. Most trees and shrubs that are buried too deeply will generally fail to thrive and eventually will die.
If you can’t see the root flare, you’ve got a problem. See the next photo.

If you’re like the majority of people who are seeing problems this time of year, you know that improper planting or severe soil disturbance is to blame. But now is not the time to fix it! You’ll need to wait until the fall, when the crown has gone dormant, to dig the plant up and take corrective action. (The “corrective action” has been discussed in this blog before; you can explore the archives or wait for an upcoming post).

These are the roots of the tree at the top of the post. No root flareNo surprise that it’s chronically water stressed in the summer, given this pathetic root system.

What you want to do right now is keep your plant as healthy as possible by mulching with coarse wood chips (not bark) and supplying them with adequate water. You DO NOT want to prune them, because that just uses up stored resources as the plant then replaces pruned material with new shoots and leaves. You DO NOT want to add fertilizer, unless you know that you have a nutrient deficiency (which you can’t know unless you’ve had a soil test. And no, those cute little diagrams of what nutrient deficiencies look like in corn leaves are worthless. You’re not growing corn here.) And DO NOT add any pesticide of any sort, even if you see signs of insect or disease damage on the foliage. With few exceptions, pesticides are broad-spectrum and you will kill beneficial species as well as any possible pests. Opportunistic pests and disease attack stressed plants, and that’s why you are seeing them.

Crown pruning just results in more crown growth. Don’t do this if you are planning to move a woody plant during the current year.

In the upcoming months, I’ll do some follow up case studies that can help you learn how to diagnosis problems. If you’re interesting in having your tree or shrub problem diagnosed and can supply sufficient information (as outlined above) and clear photos, leave a comment on this post and I’ll contact you.