What Is Root Washing – Learn About Washing Tree Roots

Tree Roots
(Image credit: Elen11)

It happens so regularly that you would think we’d grow used to it. A procedure that was drilled into our heads as being essential to a plant’s survival turns out to actually be harmful. For example, remember when experts told us to protect tree wounds with putty? Now that’s considered detrimental to the tree’s healing process.

The latest horticultural flipflop among scientists involves how to handle roots when you transplant container trees. Many experts now recommend root washing before planting. What is root washing? Read on for all the information you need to understand the root washing method.

What is Root Washing?

If you haven’t heard of or don’t understand root washing, you’re not alone. It’s a relatively new idea that container-grown trees will be healthier if you wash all of the soil from their roots before you transplant them.

Most of us were instructed firmly and repeatedly not to touch the root ball of a container tree during transplant. Botanists explained that the roots are delicate and touching them can break the smaller ones. While this is still considered true, the current view is that you can do more damage if you don’t wash the soil from the tree roots before you plant. 

About Root Washing Trees

Root washing trees is one of the only ways you can tell, before it’s too late, that your new container tree is root-bound, meaning that the roots grow in a circle around the inside of the pot. Many root-bound trees are never able to sink their roots into the soil of their new planting location and, ultimately, die from lack of water and nutrition.

The root washing method resolves this by using a hose to dislodge all of the soil in a tree’s root ball before planting. Washing tree roots with a strong spray of water gets most of the soil off but you can use your fingers for any clumps that don’t dissolve.

Once the roots are “naked,” you can determine if the roots grow in a circular pattern and, if so, cut them out. While the roots will be shorter and take longer to develop, they will be able to grow into the soil of the planting location.

Other Benefits of Washing Tree Roots

Root washing before planting accomplishes more than one beneficial end. Getting rid of any circular roots can save the tree’s life, but there are other advantages as well - planting at the correct depth, for example.

The perfect planting height is at the root flare. If you wash the soil off the tree’s root ball, you can determine for yourself the proper depth at which the young tree should be planted. Experts have long told us to set the new tree into the ground at the same depth as it was planted in the pot. What if the nursery got it wrong though?

Nurseries are notoriously busy and when it comes to getting a young seedling’s depth correct, they just cannot invest a lot of time. They may simply pop the little root ball into a bigger pot and add soil. If you get into the habit of washing tree roots before planting, you can see the root flare for yourself, the place where the upper roots leave the trunk.

Teo Spengler

Teo Spengler has been gardening for 30 years. She is a docent at the San Francisco Botanical Garden. Her passion is trees, 250 of which she has planted on her land in France.