Syringa

An upright, multi-stemmed, suckering deciduous shrub in the olive family, grown for its intensely fragrant mid-to-late-spring (May) bloom of lilac-purple flowers in large conical panicles. Native to southeastern Europe and cultivated in North America since the early 1600s, it matures to 12-16 feet tall with blue-green, pointed-ovate to heart-shaped leaves. It needs cold winters and cool summers — and offers few ornamental features after bloom, with leggy form, no fall color, and summer powdery mildew.

Persian lilac (Syringa × persica) is a compact deciduous lilac (Oleaceae) of uncertain hybrid origin, thought to arise from a cross between Syringa × laciniata and S. afghanica; it has been cultivated in European gardens for centuries and carries no confirmed wild native range (Wikipedia). Growing 4–8 ft tall and spreading 5–10 ft wide with gracefully arching branches, it produces abundantly fragrant pale-lilac panicles in spring and tolerates more warmth than common lilac (USDA zones 4a–7b per NC State Extension; some sources extend the warm edge to zone 9). The honest catch is powdery mildew: this lilac is highly susceptible and must be sited with excellent air circulation and pruned to an open centre, or the mid-summer foliage will be heavily disfigured — a near-certainty in humid, sheltered spots. (Note: this is the Oleaceae lilac, NOT the toxic Melia azedarach that shares the name.)