A lilac shrub is a woody, deciduous, flowering plant of the olive family. Lilac flowers range in color from snow white to deep burgundy, however, the vast majority are a delicate, light purple. Generally a hardy plant, lilacs will usually do well in any setting that has good soil drainage, frequent watering, and full sun. While they will tolerate warmer climates, lilacs are naturally a cold-climate plant, and usually require at least a moderately cold winter to produce flowers.
Lilac shrubs belong to the genus Syringa. Within this genus, there are about 25 species that exist in the wild, all of which are native to Europe and Asia. From these few wild species, horticulturalists have cultivated as many as 1,600 varieties. While the majority of these mature to be medium-sized shrubs, dwarf varieties reach as little as four feet (1.2 m) and some tree varieties can grow up to 60 feet (18 m.)
The fragrant blossoms appear as clusters — termed thryses — that can reach up to 8 inches (20 cm) in length. Each cluster contains multiple four-petaled flowers. The petals of each flower fuse to form a long, tubular base. Within the flower, both the pollen-producing anther and the pollen-accepting stigma are housed, making the lilac a perfect, or bisexual, flower. This arrangement allows the lilac shrub to self-pollinate if necessary, producing offspring that are an exact genetic replica of the parent.
Lilacs typically grow best in plant hardiness zones three, four and five. While they are capable of growing, and even thriving, in areas warmer or cooler than this, a particularly hardy cultivar or favorable micro-climate is usually required. Flower buds, produced in the fall, require a lengthy dormant period to form blossoms in the spring. For most regions, a lengthy winter fulfills this need. In warmer climates, some varieties of lilac have been shown to bloom following an extended drought period.
Generally speaking, a lilac shrub will do best if planted in a site with sandy, loam soil at a slightly alkaline pH. Other site requirements include good sun exposure, with full sun preferred, and a steady water supply. Lilacs require little in the way of feeding. A moist mulch of compost applied just after blooming is normally sufficient. Overfeeding, feeding too late in the year, or using a fertilizer too high in nitrogen can potentially discourage blooming, or leave the lilac shrub susceptible to disease.
While usually a hardy, low-maintenance shrub, lilacs are prone to both powdery mildew and bacterial blight. The best way to avoid these common plant diseases is to keep the lilac shrub well-maintained and healthy. Powdery mildew can usually be treated using a light sulfur spray, however, bacterial blight can sometimes require total removal of all affected foliage.