Did you plant a lilac bush and have lovely flowers the first year and nothing since then? Or maybe you’re not getting the flowers that you used to get from your established lilacs?
According to Jack Alexander, the chief plant propagator at the lilac-magnificent Arnold Arboretum at Harvard University, newly planted or transplanted lilacs tend to have transplant sulks. Most spring-flowering shrubs, lilacs included, form flower buds the previous year. That initial display you see when you buy new shrubs was set when the lilac was still comfortably at home in the nursery. When it was moved, the disturbance set it back. Give it a bit more time, and whatever you do, don’t move it again!
Common lilacs (Syringa vulgaris) and the French hybrids based on them are especially sensitive in this regard. If you’re the type who likes to move the furniture around, try planting ‘Miss Kim’ (a cultivar of S. patula). She’s a bit less fussy about an occasional relocation.
‘Miss Kim’ is easy to find at nurseries, as are a good number of S. vulgaris varieties and cultivars. But for the widest selection of colors, fragrance, and bloom times, mail order is the way to go.
Lilacs have to grow for a few years before they start flowering. After that, they bloom in spring on year-old wood, the stems that grew from the older branches during the previous summer.
Pruning consists mainly of removing elderly trunks and clipping off seed heads within reach. But if you want to cut back young growth, the proper time is right after flowering. It should be done as soon as possible, and no later than three weeks after petal fall.
Still not getting Flowers?
If you are not pruning too late or cutting off all of the new growth, the problem may be too much fertilizer, which could push vegetative growth at the expense of flowers. Or, maybe the problem is a lack of light. Lilacs need plenty of sun to flower well, and shade is the most common culprit when mature bushes fail to bloom.
Remember, too, that if you go through a summer of little or no rain, the plant will be unable to set buds for next year so you can expect little or no flowering the year after a drought.