The fragrant clusters of flowers produced by lilac trees or bushes offer gardeners proof that spring has arrived. A native of Eastern Europe and Asia, lilacs grow in USDA hardiness zones 2 to 7. The trees thrive for decades with proper care, offering gardens and landscapes plenty of color and fragrance in the spring.
Lilac trees range from 5 to 30 feet tall. The trees thrive in sunny locations protected from cold, strong winds. The trees sport pale green leaves with clusters of blossoms appearing in the spring. Blossoms come in shades of purple, lavender, blue, pink, white or magenta, depending on the variety. Most of the blossoms produce a strong fragrance that smells best on a warm, sunny afternoon when the flowers open up completely. With the exception of the Manchurian lilac, most lilac trees offer little fall interest.
More than 200 lilac cultivars exist, giving gardeners plenty to choose from. The European common lilac (Syringa vulgaris), also known as the old-fashioned lilac, features purple or white flowers on a hardy, drought-tolerant tree. For year-round interest, the Manchurian lilac (Syringa patula) offers fragrant, purplish-blue flowers. In the fall, the Manchurian lilac’s leaves turn reddish-brown. For early-blooming lilacs, Hyacinthiflora lilacs (S. vulgaris x S. oblata) do well in areas where frost seldom occurs in May. The fragrant flowers bloom 7 to 14 days earlier than most other lilacs.
Lilac trees grow best with at least six hours of sun per day. They thrive if given protection from strong winds; otherwise, the flower buds may get damaged in high winds, reducing the number of blooms appearing on the tree. Some gardeners use the trees as single specimens. Others use the trees to create hedges planted 18 to 24 inches apart. A layer of mulch helps conserve moisture.
During the months of June and July, lilac trees grow better with an extra inch of water each week since this helps set the flower buds for the following year. Once August arrives, the watering may slow down, since the plant needs to harden off for the winter. New lilac trees require no pruning during the first five years or until they reach 6 to 8 feet tall. After that, the trees benefit from a pruning after the flowers fade.
Lilac borers cause problems on lilac trees east of the Rocky Mountains. Borers are moths that use lilac trunks and branches to lay their eggs in late spring. One way to avoid borers and other pests involves providing the tree with adequate watering and soil nutrients. This helps reduce stress on the tree, making it less susceptible to pests.