Best to replace a dying ash tree

Damage caused by emerald ash borer is becoming very noticeable in the Chicago area, with dead and dying trees in home gardens, woodlands and along roadsides. The numbers of new dead trees is dwindling, since the main wave of this insect infestation has passed.

Emerald ash borer attacks ash trees and will kill them in time. The wood of dead ash trees will dry out quickly and cause the trees to become hazards, so prompt removal of any dead trees is best.

For most local gardens, it is too late to begin a treatment program to save the ash trees. Work with an arborist to determine whether or not it is too late to start treating your trees. The treatments must be done every one to two years depending on the product you use, and you will need to continue treating your trees as long as you want to save them. Otherwise, replace your ash tree with a different type of shade tree.

The Garden's website has a list of trees that are excellent replacement trees for the Chicago area. We at the Garden are continuing a program of removing and replacing ash trees on an annual basis.

• My definition of a weed is a plant that is out of place. The rainy weather this year has brought on an onslaught of weeds. A good time to weed is when the soil is moist, because the roots come out more easily.

It's very important to get weeds out before they go to seed. A small hand weeder or trowel is helpful. Look for tree seedlings such as buckthorn, mulberry and box elder that tend to establish themselves in hedges and in the base of shrubs. If you look closely, they are easy to spot.

In areas where it is not practical to dig out the roots of these weed trees, treat the stump with glyphosate promptly after cutting to kill the root system.

• Trees planted in lawns can benefit from a mulched ring to reduce competition with grass roots and to keep mowers and weed whips from damaging trunks.

If the tree is small, mulch out to the drip line of your tree. If this is not feasible, extend the mulch as far as you can. Even a 6-inch-wide mulched saucer will help protect tree trunks from serious damage. Do not mound mulch or soil around trunks because it can cause rotting at the base of the tree.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.