Lilac trees are a welcome addition to the landscape come late spring and early summer when they bloom with attractive flowers. Failure of a lilac to bloom could indicate light problems or incorrect pruning.
Tree or Shrub
While there are several varieties of lilac trees, including the popular cultivar Japanese lilac, many old lilac shrubs that have grown tall and woody are mistaken for trees. Both varieties bloom in late spring through early summer.
Failure of lilacs to bloom is most often caused by insufficient sunlight. Plants need at least five hours of bright sunshine each day to bloom well. If nearby trees or structures are reducing the amount of sunlight a lilac receives, it will not fully bloom.
Pruning at the wrong time of year or failure to prune at all can prevent lilacs from blooming. Lilacs should be pruned right after blooming. pruning any later can remove developing buds that will bloom the following year. Failure to prune older lilac shrubs will also keep them from blooming or from producing large numbers of blooms. Older lilacs should be pruned vigorously to remove old canes and to prevent crowding which prevents sunlight from reaching enough of the canes to produce blooming.