When Lilacs Fail to Bloom
> Deary Ratkins:
> My lilac bush won't bloom.
> It is 5 years old & gets a
> half-day's sun. Last summer
> I had one flower 1/2" high
> then nothing this year.
> What am I doing wrong?
The number one cause of lilacs' failure to bloom is insufficient sunlight. Ideally they have morning & afternoon sun; morning sun alone could well be insufficient. Six bright hours is the minimum, longer would be great. If the shrub isn't getting enough sun, no matter what else you do for it it won't bloom.
The number two reason for never blooming is when their narrow environmental requirements aren't met. They need very warm summers with lots & lots of sunlight, then a good solid wintry winter for dormancy; they like rather northerly climates with summer sun still shining at nine at night, followed by short winter days, like in Eastern Europe or the Pacific Northwest.
If conditions are too even year round, especially the older cultivars will forget when it's time to bloom (many newer varieties are more forgiving).So some of the commercially prepared plants are grown where they get exactly the seasons they want & are quick-shipped to market as soon as buds are big, & people buy a plant in full flower. But it's been shipped to the wrong zone & though it won't drop dead it won't easily bloom again either.
Other possibilities:
They set buds a year in advance, & untimely pruning can remove all the next year's flowers. Correct time to prune is immediately after bloom, as they set new buds the summer after blooming. Pruning in autumn, winter, or spring removes those buds.
Fertilizing with nitrogen-rich fertilizer can stop them from blooming. Kelp or bonemeal is about as much fertilizer as they can stand.
So too overwatering can stop them from setting buds. Sometimes worrying about a shrub causes a gardener to take extra special good care of it, meaning watering it way too often & overfertilizing, when it would more likely thrive on neglect.
Ours do fine in our naturally acidic soils, but sometimes they don't, & if soil is too acidic it can slow them down. Feedings of lime or wood-ash can help them flower. But don't lime the soil without knowing the pH as if it doesn't need lime it seriously doesn't need lime.
A shrub planted too deep in the ground may not bloom; it should be planted on a little hump.
It's rare that lilac buds freeze off, but if there is a harsh late freeze that hits the buds just as they come out of dormancy, they could all be killed.
There might be nothing wrong. If your shrub is really only five years old total, it would not be at all unusual that it didn't bloom until it was six years old & of substantial size, for it normally takes up to five full years before they bloom at all. Even somewhat mature lilacs pot-raised frequently take three to five full years to "settle in" from the shock of being transplanted into the garden. Six or seven years would be an unexpected length of time, but five is just within the normal range of adjustment.