Numerous species, hybrids and cultivars of lilac (Syringa spp.) are grown for the clusters of lavender, purple, pink or white flowers they produce. Most lilacs grow best in U.S. Department of Agriculture plant hardiness zones 3 through 7 and may suffer from reduced vigor and flowering in USDA zone 8 and warmer, although some lilacs, such as cultivars and hybrids of early lilac (Syringa oblata) can grow well in warmer areas.
Lilacs grow as medium to large shrubs or small tree, reaching a height of 4 to 20 feet, depending on the species and cultivar, and generally having a similar spread. These plants are deciduous, meaning they lose their leaves annually. Lilac bark is greenish-brown when young and becomes grayish-brown as it matures. Leaves are cordate, or heart-shaped, and 2 to 5 inches long. Lilac flowers are fragrant, appear in large panicles at the ends of branches and range in color from white to dark purple. Flowers develop into brown, woody capsules that contain flat, tannish seeds.
Lilacs prefer a planting site that receives at least six hours of full sun daily. They can grow well in a variety of soil types as long as the soil has good drainage. Working an organic amendment, such as well-rotted compost or aged manure, into compacted sites or clayey soils can improve drainage, as well as fertility. Lilac shrubs also prefer slightly alkaline soils.
Lilacs benefit from regular water at planting and during establishment, as well as during bloom, heavy growth periods and extended dry spells, although they are fairly drought-tolerant once established. Regularly pulling weeds from around the lilac reduce competition for water and nutrients and maintaining a 2- to 4-inch layer of organic mulch will conserve soil moisture, regulate soil temperature and suppress weeds around the lilac. Apply a balanced, slow-release granular fertilizer over the root zone of established lilacs in late winter before new growth emerges to encourage vigor. Prune lilacs each year to maintain an attractive form. Pruning is best done shortly after blooming has finished and should serve to remove spent flowers, diseased or damaged branches, a few of the oldest stems, overly vigorous or twiggy growth and all but a few of the strongest new shoots growing out of the base of the lilac.
Potential Pest and Disease Problems
Various pests and diseases can potentially prove problematic for lilacs. Both soft and armored scale insects, which appear as immobile bumps on lilac bark and leaves, suck out plant fluids, causing leaf yellowing and drop and slowed growth. Other lilac pests include mealybugs, leafminers, the lilac borer, nematodes and the Fuller rose beetle. Some pests excrete honeydew, a sticky, sweet substance that appears shiny, attracts ants and hosts the development of unsightly sooty mold. Lilac pests are generally controlled by naturally occurring predators and parasites unless these beneficial insects are disrupted by ants, dusty conditions or the use of broad-spectrum pesticides. Diseases that may bother lilacs include foliage diseases, like powdery mildew, leaf spot, botrytis blight and bacterial leaf blight, and wood diseases, such as verticillium wilt, oak root fungus and wood decay. Good sanitation practices, including removing fallen leaves promptly, avoiding overhead watering and pruning to remove infected portions of the lilac can limit the presence and impact of disease.
- University of California Statewide Integrated Pest Management Program: Syringa, Lilac, Japanese Tree Lilac -- Syringa Spp.
- Washington State University Spokane County Extension: Lilacs
- North Dakota State University Extension Service: Common Lilac
- North Carolina Cooperative Extension: In Search of Lilacs for the South
- University of Idaho: Lilac
- Cornell Cooperative Extension of Chemung County: Growing Lilacs
- University of Nebraska-Lincoln Extension: Lilacs -- Selection & Pruning
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