I have a lilac tree, I.e. Only one trunk coming up from ground. It has been among trees which have now been removed and the lilac is very straggly. It is in flower now and after it has finished flowering I’d like to prune it quite hard. Can I do this and still get flowers next year? How is the best way to go about it please?
Right after the plant stops flowering, cut back the blooms (to prevent them from going to seed) and prune back around one-third of the branches (no more than that). Start by removing dead/diseased stems and thin shoots (suckers) that are sprouting from the main trunk or the ground. Lilacs bloom on last year’s growth, but pruning right after flowering should permit new shoots to develop blooms for the next year. If you prune too late in the season, you will kill developing buds.
Is your plant a tree or a bush? For the purposes of pruning, it does not matter – these recommendations also apply to lilacs that look more like trees than bushes. However, it is important to know if your plant has been grafted, as cuts must be made above the grafts and rootstock shoots should be pruned off (as they will not produce the appropriate flowers). See also Nebraska Extension’s Lilacs – selection & pruning.
We have a lot of information already posted to our website about pruning lilacs, including:
- Pruning lilac: this also contains a few good links that provide more detailed information.
- Pruning a standard lilac tree-grafted standard lollipop shape: This includes a link to Fine Gardening’s Pruning lilacs, which discusses the importance of inspecting your lilac to determine if it has been grafted.
- Lilac candidate for rehab: This includes a link to a helpful article “Pruning lilacs – how and when to prune lilacs” from About Home.
- Lilac tree near end of life? This summary highlights that lilacs are long-lived, and also provides pruning basics.
Another excellent resource is the University of Maryland Extension’s Lilac Pruning , which provides a link to a terrific video at the University of Maine Cooperative Extension – How to prune a lilac bush.
Finally, Professor Leonard Perry of the University of Vermont, in his “Pruning lilacs properly” sets out clear “do’s and don’ts” for pruning lilacs.