Lilacs tend to bloom best on younger wood. Try to prune away about one-third of the older growth each year by cutting older branches back to the ground if the plant has multiple trunks. Thin out the older branches back to the main trunk if the plant does not have multiple trunks. The best time to prune would be right after the flowering has ceased. This will encourage new growth each year that should produce flowers in future years.
Most lilac flowers are produced on the top or terminal pair of buds. If these buds are damaged by winter cold or removed by pruning before flowering, normal flowering will be compromised.
Lilac will bloom best when planted in full sun. If it is growing in the shade, this may adversely affect flowering.
