A root shield has been placed over the cut after sucker is removed.
Closeup of hole after growing sucker has been dug out of the wood.
The shoot on its one-eighth-inch wood base.
Dealing with tree sucker shoots
Story by Michael Allen
Many trees have a tendency to send up shoot suckers through the lawn: Plums, lindens, Swedish aspens, Tower poplars, Mayday cherry and Schubert chokecherry are prime examples of such trees. Other hybrid poplars will often do the same after the tree has been cut down.
There is no easy way to eliminate these shoot suckers. You can cut them off with a lawn mower as soon as they appear, afterward locating each sucker and painting a bit of Roundup herbicide on the cut stem. Be sure not to spray the Roundup, though, as it will kill the surrounding grass.
Some people slit the grass turf between sucker shoots with a sharp spade and pull out the roots that connect the shoots. Some points of caution must always be observed when garden chemicals are being used. Do not spray when there is a noticeable breeze or wind. Protect eyes with safety glasses, hands with leather garden gloves and respiratory tracts with approved masks. Sucker shoots growing out of the base of trees like Schubert chokecherry and linden can be removed by following this labour intensive technique, which will significantly reduce the production of suckers though not completely eliminate it. Cut all the suckers as close to their point of origin as possible. Wash away the soil on top of the root crown where the suckers originated to expose the connection of the suckers with the crown. Let the root crown dry. Paint the cut surfaces of the sucker shoot stubs with Roundup.
Every second or third day over the next two weeks look for new green buds emerging either on the cut stubs or from a sharp pen knife or pruning knife dig out every visible bud, digging into the root crown at the base of the bud to a depth of one-eighth to three-16ths of an inch. Paint each opening with a tar product such as tree or wound pruning seal. Usually there is a brush applicator inside the cap of the can for this purpose. Do not use tree or pruning paint or any other type of paint as these are entirely ineffective. Be sure to cover all the cut holes. Do not cover the entire root crown. New buds will emerge later, but keep digging them out and tarring them over. Eventually fewer root crown buds will be produced in most trees.
Poplar suckers can be greatly reduced by removing the tree after all the leaves have developed in spring. At this time the roots direct their stored food to the twigs of the tree to develop new twigs and leaves. Begin the process by making two girdled cuts in the trunk with a chain saw where the tree will be taken down. These cuts should be at least the width of the chain saw blade and angled downward into the trunk. Make the two approximately parallel cuts about a foot or so apart. Into the lower girdled cut spray Roundup.
Use a plastic spray bottle with a long but narrow applicator neck so that it can be inserted into the girdled cut. Spray the Roundup uniformly throughout the cut. Wait at least a week before having the tree removed including the stump and nearby surface roots.
The two girdled cuts help stop the downward movement of sap from going into the roots. Trees tend to release their sap quickly from the top parts of the tree when they are cut. The Roundup in the lower cut will be drawn back into the roots, killing or weakening many of them. This will reduce the energy of root suckering after the poplar tree has been cut down.
Mike Allen is a consulting urban forester, certified ISA arborist and owner of Viburnum Tree Experts. He provides advisory services on tree and shrub problems. You can reach him at (204) 831-6503 or www.treeexperts.mb.ca.