Q • My lilacs, which are in their third year, did not bloom at all despite beautiful displays in our neighborhood. They otherwise seem to be in good health and have leafed out well. What is the cause of the lack of bloom? They are common varieties, one white and two purple.
A • Young common lilacs (Syringa vulgaris) are sparse bloomers until they are mature. This may take till the age of 7 to 10 years for some individual shrubs. All lilacs bloom best when grown in full sun. Make sure you’re not pruning them too late in the year. By June, buds for next spring’s flowers are already being set, so summer, fall, winter or early spring pruning may eliminate flower buds.
The proper time to prune a lilac is immediately after flowering, usually early- to mid-May in an average year in the St. Louis area. Apart from all of these points, flower buds are occasionally damaged by sub-zero winter temperatures, or more frequently, late winter/early spring frosts that strike after lilacs break dormancy. Looking toward the future, as long as your plants remain healthy and receive enough sun they will eventually flower normally for you.
Write to Chip Tynan of the Missouri Botanical Garden at firstname.lastname@example.org or Horticultural Answer Service, 4344 Shaw Boulevard, St. Louis, 63110.