Q. I have a crabapple tree that constantly sprouts up around the base. Is there anything I can do to keep this from happening? I prune them off, but they seem to grow right back. I have even tried to cover them with black plastic, but they grow right through it.

A. The vigorous vegetative shoots that grow around the base of grafted trees are known as suckers. Many small ornamental trees, including crabapples (Malus spp.), are grafted onto rootstocks for a number of reasons. Rootstocks are chosen to increase winter hardiness, impart dwarf growth characteristics or even confer disease resistance. It is very common for suckers to grow from buds on the rootstock.

They should be removed frequently, both for aesthetic reasons and to keep the tree healthy. A thick growth of suckers around the base of a tree competes for water and nutrients and impedes air circulation. They are also an easy path for insects and diseases to gain entrance into the tree.

Black plastic is a useful mulch in vegetable gardens, it and can also help keep weeds down under annual flowers. It is not as good around perennial flowers or woody ornamentals. Black plastic impedes the flow of air and water in the soil, and it can heat the soil to temperatures that can damage the roots of trees and shrubs. And, as you have discovered, it will not stop those suckers from growing.

Pruning suckers in summer results in less re-growth than pruning them in late winter or early spring. If you remove suckers when they are small, you might be able to pull them off rather than pruning them. This often removes the bud they are growing from, which means that particular bud will not re-grow.

This will not completely stop the tree from suckering because there are other dormant buds present, but it helps. Also, there are products known as plant growth regulators that can be sprayed after you prune the suckers out that will prevent re-growth for about three months.

One that might be easiest for home gardeners to find is called Sucker Stopper (napthaleneacetate), made by Monterey Lawn and Garden Products. I checked its website, but it does not list any suppliers in Western Pennsylvania. It can be purchased online; you might also ask your local garden center to order it for you.

One final caution: Never spray suckers with any type of herbicide. The herbicide can be taken up by the tree and cause extensive damage, if it does not kill the tree outright.

Doug Oster writes a blog, "Growing With Doug," exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.