Root Washing

Why on Earth would you want to wash off a plant’s roots? Don’t roots prefer being covered with soil?

Well, they do. But root washing is an excellent way to really see what the root system looks like and it allows you to correct problems before they become fatal. Root washing can provide a tree, shrub, or other woody plant with a new start on life. While the delicate roots of tender annuals and seedlings should always be handled with care, woodier roots can withstand a surprising amount of harsh treatment and are often healthier as a result.

​Wash roots to inspect packaged plants
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There are many reasons why root washing is a good idea. Being surrounded by the wrong sort of soil, arriving in the mail packed in foreign soil, or being unloaded off of a truck, wrapped in burlap, can all lead to problems. 

Hazelnut seedling with exposed roots (PickPik) Public Domain

Very often, mass-produced trees, shrubs, and other woody plants are root bound by the time they reach market. Roots can often be seen circling around the inside of the container, looking for a way out. Left uncorrected, these roots can girdle and kill the plants. Washing the roots allows you to identify the primary roots and to correct any problems.

Root pruning
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Root pruning stimulates growth the same way aboveground pruning does. Washing off the roots allows you to see them clearly and completely. Remove any dead, damaged, mushy, or circling roots. Other things to look for when inspecting root systems are knotted roots, J-hooked roots, and other deformities. J-hooked roots are roots that make a sudden turn, creating a J-shape. These roots are likely to cause problems later in the plant’s life. Once a root system has been inspected and pruned, it is time to replant it in new soil, to avoid soil interface issues.

Root bound containerized plant

Soil interface

​Soil interface refers the what happens to roots when they come into contact with a different type of soil. Very often, the soil used in mass-produced plants is a soilless mixture that contains a lot of pumice and organic material. You might expect that plants would simply move into the new soil in search of food and water, but they often don’t.  When this happens, the plant usually dies. The same thing can happen when you transplant summer annuals from high quality potting soil into more compacted, residential soil. [Believe me, I speak from experience!] Washing off the roots and installing the plant in new or resident soil eliminates this problem. You can do the same thing when planting vegetable and flower seedlings, just be very, very gentle.

Planting depth

Root washing helps you to replant the newest member of your garden or landscape at the proper depth. Bagged and packaged plants are often surrounded with extra soil. This soil is often assumed, incorrectly, to mark the proper planting depth. Planting trees at the incorrect depth is one of the most common causes of tree death. You want to be able to see the outward flare of the trunk above the soil line. Slightly too high is far better than too low.

Very often, planting holes are dug too deeply and not widely enough. Trees and their roots are best pictured like a goblet on a plate. The goblet represents the aboveground portion of the tree, while the plate represents the root system, spreading out laterally. The crown and any grafting union should always be above soil level and soil amendments are not recommended. If you suspect deficiencies in your soil, get it tested before adding anything, because too much of a good thing can be a bad thing.

How to wash roots

Now that you understand why root washing is a good idea, how do you do it?

1. Remove any container, burlap, or other packaging.
2. Shake as much soil loose as you can.
3. If necessary, soak the root ball in water to loosen the soil.
4. Gently hose off the remaining soil with a garden hose.

That’s it. Now you can inspect, prune, and replant.

Finally, rather than watering your trees and shrubs (and other plants) on a calendar schedule, invest in an inexpensive moisture meter. Containerized plants should be allowed to dry out to the point that soil pulls away from the edges of the container slightly, then water thoroughly. The water-stress symptoms of overwatering look very much like the symptoms of not enough water. Don’t guess.

Help your plants thrive with root washing and proper planting depth.