Question: Our lilac bush receives sunlight for about half the day and bloomed in the past, but not much. Now it does not bloom at all, though the foliage is healthy. It is planted in well-drained soil, and other lilacs in the neighborhood are doing well.
Lilacs are deciduous shrubs that produce clusters of flowers in mid-spring. There are several factors that could keep the plant from flowering, but the most common is the lack of sufficient sunlight. Garden experts who favor lilacs insist that they really need full sun – six or more hours of direct sunlight – to bloom.
As gardens grow and change over the years, the nature of the sunlight the garden receives may also change – trees grow taller and wider and filter more of the sunlight that gets to your garden. Could that be a factor in your landscape?
Lilacs also need adequate water in summer – not just a sprinkling around the roots, but the entire ground, says gardener Anne Owen, who has several years’ experience with growing lilacs in Middle Tennessee.
One other thing to consider is whether the plant needs pruning, which could encourage the setting of new buds and flowers next year (lilacs bloom on the previous year’s growth).
And as always, consider testing the soil. If a soil sample from your garden bed test low in phosphorous, the lilac may respond to an application of fertilizer.
In general, here is what lilacs need to grow well and bloom each spring: Full sun, well-drained soil that is lightly alkaline or neutral pH, regular water. Be aware that they are prone to developing powdery mildew. Also note that lilacs bloom best where winters are consistently cold, and they suffer in long, hot summer nights. If you live in the Southern U.S., garden expert Felder Rushing suggests planting lilacs in well-drained soil on the north side of a building, where it might be colder in winter, and hope for cool August nights.