Lilacs blossom late spring through early summer, thrive in full sun in USDA Plant Hardiness Zones 3 to 7, and appreciate some lime in their soil. Newly planted shrubs begin blooming within 2 to 5 years. While they may flower profusely some years and not others, judicious pruning is essential for abundant bloom, shape, vitality, and blossom production.
Lilacs flower on old wood, so they should be pruned immediately after flowering, or else next year's flower buds will be cut off. Remove two-thirds of the suckers and shoots near ground level, keeping a third to mature into future flowering branches. Cut larger stems from the center to allow sun and air circulation to avert disease. Sever awkward limbs to create a well-balanced, rounded shrub. If the lilac is grafted, always remove any shoots arising from the rootstock, below the graft union, to maintain the desired cultivar's flowers. Deadheading spent flowers keeps seeds from forming but is tedious and not absolutely necessary.
All are cultivars of the common lilac, Syringa vulgaris, and except for the late-season ‘Andenken Ludwig Spaeth’, they bloom in midseason. The name of the breeder and date developed follow the cultivar name in parentheses.
- ‘Edith Cavell’ (Lemoine, 1916), ultimate height 12 feet, double white
- ‘Miss Ellen Willmott’ (Lemoine, 1903), 10 feet, double white
‘Mme. Lemoine’ (Lemoine, 1890), 6–10 feet, double white
- ‘Belle de Nancy’ (Lemoine, 1891), 10–20 feet, double pink
- ‘Edward J. Gardner’ (Gardner, before 1950), 8–10 feet, double pink
- ‘Virginité’ (Lemoine, 1888), 10–20 feet, double pink
- ‘Katherine Havemeyer’ (Lemoine, 1924), 10 feet, double pink/lavender
- ‘Victor Lemoine’ (Lemoine, 1906), 10 feet, double lavender
- ‘William Robinson’ (Lemoine, 1899), 10 feet, double lavender
- ‘Adelaide Dunbar’ (Lemoine, 1916), 12 feet, double dark purple
- ‘Andenken Ludwig Spaeth’ (E. H. Wilson, 1883), 10–12 feet, single deep purple
- ‘Charles Joly’ (Lemoine, 1896), 8–10 feet, double deep purple
- ‘Olivier de Serres’ (Lemoine, 1909), 6–10 feet, double violet blue
- ‘President Grevy’ (Lemoine, 1886), 10–20 feet, double blue
- ‘President Lincoln’ (Dunbar, 1916), 10 feet, single blue