The common lilac (Syringa vulgaris) is a popular, fragrant flowering shrub known for its dense clusters of blossoms that herald the arrival of spring. This beautiful plant, a member of the olive family (Oleaceae), is often grown as a specimen shrub or used in hedges. Lilacs are not evergreen; the entire Syringa genus is composed of deciduous woody plants.
Lilacs Are Deciduous
Lilacs are classified as deciduous shrubs, meaning they naturally shed all of their leaves each year, typically in autumn. This contrasts with evergreen plants, which maintain green foliage year-round. Seasonal leaf drop is a survival mechanism that allows the plant to conserve resources and prepare for dormancy. This adaptation prevents excessive water loss when the ground is frozen, allowing lilacs to thrive in cold climates, withstanding temperatures as low as -40 degrees Fahrenheit. The lilac requires a substantial period of winter chill to properly set its buds for the following season. Without this cold period, the plant’s flowering potential is significantly reduced, but this natural cycle ensures robust blooming once late spring returns.
The Annual Cycle of a Lilac Bush
The lilac’s annual cycle begins with fragrant blooms in late spring, followed by vegetative growth throughout the summer. As daylight shortens and temperatures drop in the fall, the shrub begins senescence, preparing its leaves to drop. Unlike some deciduous plants that display vibrant fall colors, common lilacs often show little change before the leaves brown and fall away. By winter, the lilac bush is reduced to bare stems, confirming its deciduous status. During dormancy, the next season’s flower buds are already formed and visible on the branches. These small, rounded buds are distinct from the smaller, more pointed leaf buds.
Dormancy and Winter Care
The dormant period is a time of reduced metabolic activity for the lilac. Preparing the shrub for winter ensures its survival and promotes a strong bloom the following spring. Before the ground freezes completely, provide the shrub with a deep watering to ensure hydration. Applying a three to four-inch layer of organic mulch around the base of the plant helps regulate soil temperature. This mulching prevents “winter heave,” which is the exposure of roots caused by the repeated freezing and thawing of the soil. Pruning for rejuvenation is best done immediately after the shrub finishes flowering in late spring, as winter pruning removes the upcoming season’s buds. However, removing any dead or damaged branches can be done at any point during the dormant winter period.