September 16, 2009
Q. My two-year old lilac did not bloom this year or last year. Any ideas why?

A. This is one of the questions most frequently asked of Master Gardeners in Ontario. Here are some of the most common reasons that your lilacs didn\'t bloom:

  • You may have inadvertently pruned off the new flower buds last year. The new buds form shortly after the flowers die back. Prune in spring immediately after the blooms have faded. Cut just below the faded bloom.
  • The bush is immature. Most varieties need a few years to grow and develop, before they produce their first blooms.
  • A pH imbalance or too much or too little of certain chemicals. You might want to have your soil tested.
  • Too much nitrogen/ not enough phosphorus. Sometimes, people use high nitrogen fertilizers, especially for their lawns, which will help produce green leaves, while hindering blooming.
  • Too shady a site. Without enough sunlight, the plant often will not bloom. Lilac bushes prefer full sun.
  • Transplant shock. You may just have to give your lilacs another year to get over this.
  • Sometimes a late freeze can knock the flowers or the start of the flowers right off the bush. If your lilac bush is not blooming, you might want to think back and think about whether or not there was a late freeze. If this is why your lilac bush is not blooming, your bush is fine. Next year, you should have a ton of blooms.
  • There are some pests that can prevent lilac flowering as well. These include scale insects and borers which cause damage within the stems of the bush. You can see scale insects pretty easily on the leaves of the bush. If you see them, you will need to treat your bush so that it will do well the next lilac blooming season. If you see borer damage, you can alleviate this by pruning the affected wood. This way new growth will come back without the damage from the borers and your lilac flowering will resume the very next season.
Linda Hugli
Master Gardener