Common Lilac

Common Lilac is an upright, multi-stemmed deciduous shrub that grows 10 to 20 feet tall with an irregular outline and somewhat leggy branching habit. You identify it by the large, upright clusters of flowers (up to 20 centimeters long) that bloom in May, typically in lavender or white with four-lobed, tubular blooms, each intensely fragrant. The leaves are opposite, simple, ovate to broad-ovate, dark green, sometimes almost bluish-green, and measure 5 to 13 centimeters long. As the shrub matures, secondary shoots emerge from the base and roots, sometimes producing small clonal thickets over decades. Gray to gray-brown bark is smooth on young stems but becomes furrowed and flaking on older wood, adding winter structure to the garden.

You will find Common Lilac prefers full sun for best flowering, though it tolerates light shade; avoid full shade, which diminishes bloom production. The plant grows better in colder climates and prefers neutral to slightly alkaline soil with good drainage; it tolerates clay and medium salinity. In Western Washington at the warm edge of its ideal climate, select disease-resistant cultivars where possible. The species produces hundreds of cultivars; 'Ludwig Spaeth' and 'Sensation' are available in trade and offer distinct flower forms. This shrub blooms on previous season's growth, so prune immediately after flowering through early summer to shape without sacrificing next year's buds. Watch for powdery mildew, bacterial blight, and several leaf diseases in the PNW, along with occasional pest pressure from oystershell scale and lilac borer.