Sharon Nies, sales associate at Hinsdale Nurseries, Willowbrook

Joel Barczak, co-owner of Blumen Gardens, Sycamore

“Usually when lilacs don’t bloom they’re not getting enough sun. Another possible cause is incorrect pruning. Lilacs should be pruned right after they bloom. There’s a 2-week window when this can be done. Often a landscaping company will come in and prune everything in the fall. If you do that with lilacs, you’re cutting off the next season’s bloom.”

“My experience is that lilacs need a certain amount of maturity before they bloom. Also, over-feeding with a high nitrogen fertilizer would produce leaves at the expense of flowers. They bloom on old wood, so pruning in the fall or early spring would cut off the flower buds. Shade will diminish the amount of bloom but not totally eliminate it.”

Wally Schmidtke, garden center manager, Pesche’s, Des Plaines

Bob Waterman, Director of Gardens and Grounds at Cantigny Gardens, Wheaton

“I’m a firm believer that lilacs have to be pruned as soon as the flowers dry up. Lilacs love our clay soil, but many people prune them in the fall, which cuts off flowering buds and may confuse the plant for a couple years afterwards I’m also a fan of organic fertilizer, sprinkled around the base of the plant in early spring and again in fall. Don’t use a weed-and-feed fertilizer on the nearby lawn. It gives them too much of a nitrogen blast. “

“We have a variety of lilacs at Cantigny, and when people ask us about their very old lilacs that have stopped blooming, we recommend the 1/3 pruning technique. Let’s say you have
a shrub with 12 stems. Take out the four largest and cut them right down to the ground. Do this in late spring or early summer.”