Lilacs typically bloom in late spring, usually around May, with the flowering period lasting from two to six weeks depending on the species and geographical location. Some early blooming species may flower as soon as spring begins, while late-blooming varieties can extend into early summer. Lilacs need cold winters for proper chilling to develop flower buds, full sun exposure (at least six hours per day), and proper pruning shortly after blooming to promote healthy future blooms. Re-blooming varieties like Bloomerang lilacs can bloom again from mid to late summer into fall.