Gardening Q&A: Tree is down, but its roots keep sending up shoots

Q. I’ve cut down a crape myrtle tree and now I now have them sprouting up all over the place. Do you have any ideas on how can I get rid of these? — Josephine Hargrave, Portsmouth

Many trees and shrubs respond to pruning, and particularly severe pruning (as in your case, complete tree removal), by producing adventitious shoots from the trunk, the roots or both. Mechanical injuries to the crown and roots, as from lawn mowers or clippers, may also induce sprouts to grow. Plants may produce sprouts as a survival response to replace stems lost to herbivores and fire.

Though you have decapitated your tree, it is not dead; the roots remain very much alive. What you’ve done is to send your plant into panic or survival mode. Deprived of the above-ground photosynthetic apparatus that is vital to its survival — its leaves — what is left is desperately clinging to life. It is in a battle for survival and is not going down without a fight.

Because roots are out of sight, many of us don’t have a clue how important they are and how they function. And it was not until fairly recently that research has elucidated much of this.

Although the root system weighs far less than the rest of the tree (the root-to-shoot ratio for trees under normal conditions is usually about 1-to-5 or 1-to-6 by weight, according to the Journal of Arboriculture), the roots take a lot of space. They typically occupy the top 6 to 24 inches of soil and an area two to four times the diameter of the crown, according to the Colorado State University Extension. These extensive root systems anchor the tree and absorb water and nutrients. They also store carbohydrates that were manufactured by the leaves above. It is these stored reserves that give the stump and roots the wherewithal to keep fighting back.

Whether the problem is root suckers or basal sprouts (on the crown), the solution to your problem boils down to three options: mechanical, chemical or both. With a large tree, grinding out the stump and its large roots is the best route. Though it can be expensive, consider the headaches it may save you down the line.

If the tree is small, you may be able to cut it flush to the ground and keep sprouts at bay by mowing, applying chemicals, or both. Cut-surface treatments are applied by painting freshly cut stumps or stubs with a concentrated systemic herbicide. The chemical is absorbed and travels to the root system through the vascular tissues. Glyphosate, triclopyr and picloram are commonly used and sold under various trade names and formulations that fit the job. Foliar sprays can be applied directly to sprouts using those and other broadleaf weed killers containing 2,4-D.

Repeat applications, over several seasons, may be necessary until the roots are completely dead. Always take care to follow the label directions and to avoid spraying species you’re not targeting.

If you are diligent at keeping emerging sprouts from developing, eventually the roots will die, and the problem will be permanently solved. Persistence is key.

And one more thing

With summer right around the corner, unfortunately the precipitation deficit of last year continues: Each month this year has been in the minus column. Keep a good eye on all your plants, including any you put in last fall and winter.

What’s going on in your garden this year? Doing something differently or trying something completely new? Drop us a note.

Send questions to wkspen@gmail.com