Delicate and deliciously fragrant, lilac shrubs have all the hallmarks of a prima-donna plant. The flowers have even christened a color and named a fragrance. But behind the romance, abundant purple blossoms and that heady smell, they are surprisingly easy to grow and care for. If you take the time to plant your lovely lilacs appropriately, you may find that they are among the lowest-maintenance plants in the garden.
Like the song of the house finch, the scent of the lilac signals the arrival of spring. The most familiar species, common lilacs (Syringa vulgaris), are long-lived woody shrubs that put on a vibrant flower show for two weeks in springtime. They produce long clusters of gorgeous flowers, usually a shade of purple/lavender/blue. But there are 20 other lilac species that grow wild around the planet, as well as hundreds of cultivars in different hues and sizes.
Generally, lilacs thrive in colder climates, growing best in U.S. Department of Agriculture plant hardiness zones 3 through 7. They require a period of winter chill to bloom. However, breeders are working to create new varieties of lilacs that have a higher warmth tolerance.
To keep your new lilac healthy, check your cultivar's hardiness zone and make sure it is said to grow well in your region. Then select a site for the lilac. Plant it in a spot where it will get at least six hours of sun, for best flower production. Lilacs need fertile, well-drained soil with a pH close to 7.0. If your soil doesn't live up to this description, add organic compost and work it in.
Select a spot where your lilac can grow to its mature size without any obstructions. The average mature height varies between 5 and 15 feet, but individual cultivars can be taller. Some "shrubs" are as big as apple trees. When to plant? You can transplant your shrub in spring or fall, although fall is slightly better.
Caring for Lilacs
If you schedule hours of "lilac" time in the garden, most of it can be spent admiring the blossoms and scent of your shrub. That's because lilac care won't take much of your time.
In spring, apply a layer of organic compost to the soil beneath the shrub. On top of that, add a mulch like chipped bark to keep down weeds and control soil temperature. In summer, you'll need to be sure the shrub gets an inch of water a week, either through rainfall or irrigation. In late winter, feed the shrub with a handful of granular 10-10-10 fertilizer tossed on the soil and watered in.
The only type of lilac care that might take a little time is pruning. You'll want to trim your lilac shrub right after it blooms to shape it and remove dead or damaged canes. At the same time, remove any suckers growing at the base of the plant. Don't prune later in the summer, since lilacs bloom on old wood. After you prune out dead canes, remove a few of the oldest canes by cutting them off at ground level. Trim back weak branches to just above a strong shoot. Tall canes should be cut to eye level.
To rejuvenate an old, out-of-shape lilac, cut one-third of the oldest canes back to ground level. The next year, cut back half of the remaining old canes. In year three, cut back the rest. Severe pruning can cause flower loss for a few years, so save it for extreme cases. Doing regular annual maintenance pruning is easier for you and better for the plant.
From Alaska to California, from France's Basque Country to Mexico's Pacific Coast, Teo Spengler has dug the soil, planted seeds and helped trees, flowers and veggies thrive. A professional writer and consummate gardener, Spengler has written about home and garden for Gardening Know How, San Francisco Chronicle, Gardening Guide and Go Banking Rates. She earned a BA from U.C. Santa Cruz, a law degree from U.C. Berkeley's Boalt Hall, and an MA and MFA from San Francisco State. She currently divides her life between San Francisco and southwestern France.