Choose lilacs carefully, or end up with high-maintenance shrub – Chicago Tribune
The sight and fragrance of lilacs, blooming in shades from deep violet-purple to pink to white, are among the splendors of spring.
If you’d like to have that splendor in your yard, be careful about the lilac you choose, said Julie Janoski, Plant Clinic manager at The Morton Arboretum in Lisle. “They’re glorious for about two weeks in May, but the rest of the time, old-fashioned lilacs can be a lot to handle,” she said.
The most familiar species is common lilac (Syringa vulgaris), a plant from the Balkans that is popular around the world and has been planted in Chicago-area gardens since the 19th century. Many decades-old lilacs survive today.
Mature shrubs are often 15 to 20 feet high and just as wide. “They are vigorous, spreading shrubs that need a lot of space,” Janoski said.
If a lilac needs to be pruned, do it soon after the shrub finishes blooming. “If you wait too long, you will reduce the spring bloom next year,” she said.
That’s because lilacs develop next year’s flower buds over the course of each summer. “You have a window of three or four weeks to prune,” Janoski said. “After that, you’ll be cutting off next spring’s flowers.”
Lilacs try to form clumps by sending up new shoots from spreading roots. “Prune out the suckers to keep the lilac under control,” she said.
An old lilac often becomes a dense tangle of thick, gnarly old stems, dead wood and new shoots. This crowding can impede circulation and encourage powdery mildew, a common problem with older varieties of lilac. Opening up the interior of the shrub by pruning can improve air flow and restore vigor.
There are two ways to tame a tangled old lilac: renewal pruning and rejuvenation pruning.
For a gradual approach that keeps lilac blooms coming every spring, try renewal pruning. First remove all the dead wood, cutting dead stems as low as you can. Then remove the thickest, oldest living stems, pruning them off within 1 or 2 inches of the ground. “Take out only one-third of the living stems,” Janoski said. The remaining stems will support the shrub with their sun-gathering leaves and will bear spring blooms.
In each of the next two years, remove one-third of the oldest stems, and keep removing dead wood. By the fourth year, all the stems will be younger and more vigorous. “After that, check each year and prune as necessary to keep the big tangle from returning,” she said. “Always remove the oldest stems, and make sure you never take out more than a third of the plant.”
For a more drastic, less painstaking approach, try rejuvenating the shrub. Cut off all the stems — the whole plant — within 1 or 2 inches of the ground. Next year, new stems will sprout, but they won’t have blooms. “You’ll lose a year of flowers,” Janoski said. The first blooms will appear the following spring, and it will take a few years for the shrub to get back to its full size.
Not all lilac problems can be solved by pruning. For example, it won’t restore bloom to a shrub that is in too much shade.
Lilacs in nature only grow in full sun in well-drained soil, according to Kris Bachtell, vice president of collections and facilities at the Arboretum. Without full sun, they won’t bloom.
In gardens, old lilac shrubs that were planted in full sun may now be in shade because trees have grown overhead or newer buildings now block the sun’s rays. “There’s nothing you can do to make a lilac bloom if it doesn’t have enough sun,” Janoski said. “It’s just a large nonflowering green shrub.”
For gardeners who don’t have the space or patience for an old-fashioned lilac, several more manageable species and cultivated varieties are available. These smaller lilacs usually do not require as much pruning as old-fashioned lilacs, needing only occasional pruning for shape.
Meyer lilac (Syringa meyeri) grows 6 to 8 feet high and wide. Although it blooms best in full sun, it can tolerate part shade. It blooms slightly later than the common lilac. The most common cultivar is Palibin.
Manchurian lilac (Syringa patula) is known mainly for one cultivar, Miss Kim. It has fragrant light purple flowers that fade to light pink on a plant that is 5 to 8 feet tall.
Reblooming lilacs are hybrids that bloom again in late summer or early fall, although not as lushly as in spring. The Bloomerang series includes several cultivars, including Bloomerang Purple (Syringa ‘Penda’); Bloomerang Dark Purple (Syringa x ‘SMSJBP7′); and Bloomerang Dwarf Pink (Syringa x ‘SMNJRPI’). They are all smaller than the common lilac, but sizes vary among cultivars, so research each plant and choose the right size for your yard.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or firstname.lastname@example.org). Beth Botts is a staff writer at the Arboretum.