Although many lilac varieties bloom in midspring commonly around May the Excel cultivar blooms as early as February or March. Typically blooming in late spring it offers the largest flowers with the best fragrance. Why Your Lilac Bush Isn T Blooming And What You Can Do About It Natalie Linda Lilac Bushes Flower Garden Care Flowers Perennials Click to see full answer. When are lilacs in season . The dense fine branches are clothed in small dark green broadly-ovate leaves that remain attractive in summer. Unfortunately lilacs back then only bloomed for a few weeks in spring. 6 Flower Type and Fragrance. Planting a variety of lilac species and hybrids can provide continuous fragrance and extend the bloom time into early summer. Lilacs need pruning immediately after blooming to promote flowering the next year. In the language of flowers lilacs hold the symbolic meaning of the joy of youth. Blooming in late spring to early summer this pretty lilac often repeats bloom i...