The lilac (Syringa spp.) is a classic shrub known for its fragrant display each spring. Although these flowers are often associated with summer, traditional varieties do not bloom continuously throughout the warmer months. This article clarifies the typical bloom cycle of common lilacs and introduces modern cultivars engineered for extended flowering.
The Standard Bloom Period
The common lilac, Syringa vulgaris, is known for its relatively brief flowering period. In most climates, the standard bloom lasts only two to four weeks, typically beginning in mid-to-late spring. This short duration is dictated by the plant’s natural biology and how it develops flower buds.
Traditional lilacs are classified as “old wood” bloomers, meaning they produce flower buds on the growth from the previous year. Immediately after the current season’s flowering concludes, the plant begins forming the buds for the following spring. This cycle prevents the shrub from sustaining blooms all summer long.
Once spring flowering is complete, the plant diverts energy into vegetative growth, producing new leaves and stems. This new growth initiates the next set of buds for the following year, preventing the production of new flowers during the current summer.
Lilac Varieties That Rebloom
Fortunately, plant breeders have introduced modern cultivars that overcome the short bloom cycle of traditional varieties. These re-blooming lilacs offer a solution for those who desire flowers beyond the spring flush. They achieve extended flowering by having the genetic ability to bloom on both old wood and new wood.
The most recognized examples are varieties in the Bloomerang series, such as ‘Dark Purple’ or ‘Dwarf Pink’. These lilacs produce a strong first bloom in the spring, similar to traditional types. After this initial show, the plant rests briefly to establish new growth.
Once that new growth matures, the shrub produces intermittent, smaller flushes of flowers from mid-summer and often continues into the fall. This ability to bloom on the current season’s growth effectively extends the lilac season by several months. These cultivars tend to be smaller than the common lilac, making them excellent choices for smaller gardens or container plantings.
How to Maximize Your Lilac’s Flower Production
Regardless of whether you grow a traditional or a re-blooming lilac, proper care maximizes the flower display. Sunlight is a primary factor, as lilacs require a minimum of six hours of direct sun exposure daily for optimal flower production. Planting the shrub in full sun is essential for a healthy, floriferous plant.
Proper pruning technique is also important, and the timing depends on the type of lilac. For standard Syringa vulgaris, pruning must be done immediately after the spring bloom fades. Delaying pruning into the summer or fall removes the newly set flower buds for the next year, resulting in no blooms the following spring.
Removing spent flower heads, known as deadheading, is another helpful technique. Cutting off faded flowers directs the plant’s energy away from seed production and toward developing the following year’s flower buds. This practice is beneficial for younger shrubs or any lilac where flower production is a priority.
Lilacs are generally not heavy feeders, and excessive fertilization, especially with high-nitrogen formulas, can suppress flowering by promoting leafy growth. If you choose to fertilize, apply a balanced formula or one higher in phosphorus, which supports flower development, in the early spring before the buds swell. Ensure the soil is well-draining, as lilacs do not tolerate wet conditions.