Last fall, I transplanted some lilacs from a friend’s yard. In the spring, new leaves appeared, but only on the tips of the branches. It is now past time for pruning lilacs, but I didn’t dare do it. There would have been hardly any leaves left! What should I have done?
Danielle Nolin, Quebec
We gardeners have this unfortunate habit of always wanting to prune things, but in fact, pruning is rarely necessary. In the case of the common lilac (Syringa vulgaris), which is almost certainly the one you dug up, there are essentially three kinds of pruning you could do, none of which is absolutely necessary. And most certainly, none applies to a lilac planted less than a year ago. The only pruning such a young plant might possibly need would be removing any dead branches that occur.
3 Types of Pruning
Here are the 3 types of pruning lilacs may need and when to apply them.
Deadheading: pruning faded flowers
Deadheading sounds dramatic, mais simply means removing faded flowers. That will be unnecessary in your case, because your lilac is unlikely to have bloomed yet. You can expect the first blooms when it is about 4 to 7 years old. This kind of pruning is popular with many gardeners, as it fulfills our need to prune something. Anything! However, it’s not terribly useful. In fact, even the International Lilac Society admits that this popular practice is essentially useless.
In theory, it’s mainly done to “stimulate better flowering the following year” by keeping the plant from going to seed. The idea is to cut back the flower spikes before they start to produce seed capsules. However, whether you remove the seeds or not, lilacs all tend to follow a major flowering season with a weak one. So, deadheading really doesn’t improve bloom. The removal of faded flowers is therefore strictly a matter of aesthetic concern, for those who find the seed pods unpleasant to the eye.
If you insist on doing it, you must remove the flowers in June, immediately after flowering. That’s the pruning you were concerned about. August is indeed far too late now. But again, this doesn’t even apply to your baby lilacs. They didn’t bloom and you can’t deadhead a plant that doesn’t bloom! Simple!
As for renewal pruning, this is done by removing the oldest branches every two or three years to make room for the youngest. You would do this to well-established lilacs, not young ones like yours. Your lilac won’t need renewal pruning before at least four or five years.
The same is true rejuvenation pruning, where very old lilacs are cut down almost to the ground to stimulate recovery from the base. These two prunings can be practiced in any season … but a freshly transplanted young lilac absolutely does not need them.
So, just let your young lilac grow on its own for the moment. Any pruning is many years further in the future!