(Question)
I have two lilac bushes about 5 years old. 3 and 4 years ago they produced many flowers. Two years ago no flowers. This year, two flowers. I have carried out minor pruning after the flowering season each year. What else would you suggest?
Thanks
(Answer)
Thank you for contacting the Toronto Master Gardeners concerning your lilac.
There are several possibilities why your lilac had few blooms this year. For example:
- During pruning last year new buds might have been cut off in error. Lilacs need be to be pruned soon the flowers fade. Cut just below the faded bloom.
- Using a fertilizer with too much nitrogen and not enough phosphorus on the shrub or the lawn produces green leaves, while hindering blooming. I suggest using a high phosphorus fertilizer, something with a higher middle number (5-30-5 as an example).
- This year there was a late freeze in Toronto which could have knocked the flowers or the start of the flowers right off the bush.
- Older lilacs lose their vigor and number of blooms as they age.
- Some insects such as scale insects and borers damage the stems. Have you seen evidence of the insects on the leaves of the lilac?
- Have you amended the soil? It is ideal to add organic material in the fall (compost and shredded leaves) and to mulch in the spring.
For more information about blooming problems with lilacs please see:
https://landscapeontario.com/qa-why-are-there-no-blooms-on-my-lilac
https://www.chicagobotanic.org/plantinfo/faq/lack_flowers_lilacs