Lilacs (Syringa sp) are a favorite ornamental shrub in planting zones 3 through 7. Once established, the shrubs are easy to maintain and will produce masses of fragrant purple, pink or white blossoms each spring. Lilacs can be trimmed into hedges, used in border or foundation plantings, or as specimen plants. They prefer full sun and well-drained soil. Lilacs produce blooms on stems that are at least three years old. Regular pruning of your lilac will keep it healthy and blooming.
Cut one-third of the woody lilac branches to within a few inches of the ground. Use sharp pruning sheers, and do this in summer after the lilac has bloomed.
Trim away spent blooms in the spring. This prevents the lilac from expending energy going to seed and will encourage better blooming the following season.
Cut back one-half of the branches you didn't prune the year before during the second summer.
Cut the remaining old branches the third summer. Pruning back one-third of the bush each year keeps the lilac from getting too cumbersome and unproductive. Eliminating very thick woody branches also protects the lilac against wood borers.