Cultivars of the common or French hybrid lilac (Syringa vulgaris) often do not bloom for several (five or more) years after planting. The shrubs must grow and mature before they are capable of flowering. Selecting a favorable planting site and good cultural practices during establishment encourage lilacs to flower as quickly as possible.
Lack of Flowers on Common Lilacs
Lilacs perform best in well-drained soils in full sun. Plants should receive at least six hours of direct sun each day. Lilacs planted in partial shade will not bloom well.
Good care during the first two to three years is also important. Apply a 2- to 3-inch layer of mulch around each shrub to conserve soil moisture and control weeds. Water lilacs on a regular basis during dry weather. Also, protect lilacs from browsing rabbits by placing wire fencing around the shrubs in fall.
While good cultural practices will aid plant growth, some practices may actually inhibit flowering.
It is generally not necessary to fertilize lilacs. However, lilacs can be lightly fertilized in early spring. Heavy fertilization may promote excessive vegetative growth and discourage flowering.
Pruning can also affect flowering. Lilacs bloom on the previous year's growth. The best time to prune lilacs is immediately after flowering in spring. Pruning lilacs in late summer, fall, or winter may remove many of their flower buds.
While the common lilac usually doesn't bloom for several years after planting, several other lilacs bloom when quite small. The dwarf Korean lilac (Syringa meyeri), 'Miss Kim' lilac (Syringa pubescens subsp. patula 'Miss Kim') and Preston lilacs (Syringa x prestoniae) often flower within one or two years of planting.