Lilacs not Blooming?

Your lilac plant appears healthy but had little or no flowers at blooming time.

Here are some possible explanations for its lack of bloom:

• Your plant is too young and may require two or three years to become mature.

• Inadequate sunlight. Lilacs need as much direct sun as possible to ensure mature growth to flower.

• When removing flowers, you may have cut back too far. Only cut as far as into the second pair of leaves from the tip of the branch.

• Inadequate fertilization. Use an all-purpose fertilizer (high in phosphorus and potassium) just after blooming. Avoid excessive use of high-nitrogen fertilizer or other materials that create too much leaf growth.

• Root damage due to planting, construction or nearby digging.

• Drying out. Try to keep plants evenly mulched and watered.

• Biennial blooming. Flowering in alternate seasons may occur with different cultivars.

• Plants are too old. They may need a rejuvenating pruning to encourage young flowering wood. Cut back your lilac hard to within two feet of the base and thin out any weak stems. It will take a couple of seasons to recover but you will wind up with more flowers and they will cover your lilac.

• Insect or disease damage. Control accordingly.

• Cold winter. The cold may have damaged young flowering shoots.

Conway Lum is a horticulturist at Mandeville Garden Centre in Burnaby. Questions can be emailed to him at clumATcanadawideDOTcom.