Lilacs range in size from large shrubs to small trees. The leaves are opposite (occasionally in whorls of three), deciduous, and in most species simple and heart-shaped, but pinnate in a few species . The flowers are produced in spring, flowers can be white, pale pink or more generally purple, with four petals. The flowers grow in large panicles, and in several species have a strong fragrance.

Lilac bushes can be prone to powdery mildew disease, which is caused by poor air circulation.