Lilacs are one of the most cherished and adored of all flowering shrubs. They are noted for their beautiful blossoms and fragrance. Lilacs are available in a wide range of colors. Though they offer mainly one season of interest, their spring flower displays are greatly appreciated after a long, hard winter.
If you have lilacs or are interested in planting one, there are several factors to consider.
Lilacs are adapted to USDA Hardiness Map zones 3, 4, 5, and milder areas of zone 2. They thrive in sunny sites with good air circulation. Lilacs on their own roots are far more hardy than grafted lilacs. Lilacs need at least 4 to 6 hours of sunlight a day for best flower production. These suckering shrubs tolerate a wide range of soil conditions but grow best in moist, well-drained soils. Excessively wet conditions are not well tolerated. Depending on the species, blooms begin in late April and early May and continue through mid-June. Shrubs should be spaced between 10 and 15 feet apart for specimen displays and 5 to 8 feet apart for a hedge effect.
The spent flowers on lilacs aren’t very attractive. Removing the spent flowers (deadheading) improves the appearance of the shrubs and prevents seed pods (capsules) from forming. Deadheading allows the lilacs to use much of their energy for next year’s flower bud development rather than seed pod formation. As a result, lilacs that are promptly deadheaded after flowering often bloom more heavily the following season than those that are not deadheaded.
When deadheading lilacs, make the pruning cut at the base of the flower cluster and just above the uppermost leaves.
While deadheading is beneficial, removing spent flowers may be challenging for home gardeners with large numbers of lilacs. Shrubs will still bloom in subsequent years even when not deadheaded.
Lilacs set their flower buds for the following season in mid-summer, not long after the spring blooms fade. Pruning shrubs immediately after flowering is the best time to prune lilacs and will help the lilac produce the most flowers the following spring.
Lilacs respond best to the removal of select branches at their point of origin or entire branches from the base of the suckering shrub rather than with shearing or clipping. This strategic removal of branches preserves the shrub's natural shape. Removing the oldest and largest branches within 6 to 8 inches of the base every 3 to 5 years can also reduce the overall size of the shrub and promote new growth that blooms better than older stems. Large old branches can be removed immediately after flowering or in late winter (March or early April). When pruned in late winter, some blooms will be sacrificed, but larger branches are often not as floriferous, and it is much easier to see and remove the branches when the plant is dormant and without leaves.
When lilacs become large and overgrown, the pruning requires more consideration. Learn more about pruning overgrown lilacs in this article: Pruning Large, Overgrown Shrubs.
Lilacs offer gardeners a large variety of plant shapes, sizes, and flower colors. Hybridizers have worked extensively with the common lilac resulting in over 1000 different varieties. There are seven color classifications for lilacs: white, pink, violet, blue, magenta (reddish-purple), lilac, and purple. Flowers are also available in single and double forms.
Many are familiar with the common lilac (Syringa vulgaris), but several other species and dozens of cultivars are available to gardeners. Some species will bloom as early as late April and early May; others can flower as late as mid-June. Learn about the many species and types of lilacs that can be grown in Iowa in this article: Lilacs Species for Iowa Gardens.
Overall, lilacs are easy to care for and problem-free shrubs. Occasionally, problems arise like failure to bloom, flowers opening out of season, powdery mildew, and other disease or insect issues.
Learn more about how to solve potential problems growing lilacs in this article: How to Manage Potential Problems Growing Lilacs.
Lilacs are best propagated by softwood cuttings. Softwood cuttings are taken in late May through early July from the current season’s growth. More information and step-by-step instructions on how to propagate by softwood cuttings can be found in this article: Propagation of Deciduous Trees and Shrubs from Softwood Cuttings
- A lilac that was planted three years ago has never bloomed. Can I do anything to encourage the lilac to flower?
- Why is my lilac blooming in fall, instead of spring?
- The leaves on my lilac are covered with a white substance. Is this a serious problem?
- I have oystershell scales on my lilac. How can they be controlled?