All lilac bushes benefit from regular attention. The purpose of pruning a lilac is to shape the plant and increase bloom quality. This is all part of regular garden maintenance.
It normally consists of removing dead or diseased branches and shaping up the shrub. Occasionally, we prune to reduce size and renew the health of the bush.
Springtime is Best
Like most spring blooming shrubs the best time to cut away branches is directly after the flowers bloom. Lilacs will begin to set buds for the following year, pruning after they finish flowering will encourage the strength of the plant to grow and set flower buds.
Lilacs will begin to set buds for the following year shortly after they finish blooming. This is why we prune immediately after flowering. All flowering branches removed after this window will diminish the flowers for the following year.
How To Prune
When too many shoots grow straight up from main branches or grow inwards, it is time to remove them. The goal is twofold: increase airflow within and the overall shape and appearance.
Remove new growth flush with the bark, older branches around a collar of where it joins into another branch. Generally cut at an angle with sharp blades which leave a clean cut.
For most shaping a hand pruner works well. I grub off very small growth along the main branches with my hand. Most large branches can be taken off with loppers
Renew an Old Lilac
If you have very old lilacs which are looking poorly, pruning the entire plant down to about 1.5 to 2 feet will renew it.
I did this with the original ancient shrub growing in my front yard. Old branches riddled with borer, and a lost center meant it needed help.
Pruning large shrubs
Overgrown Shrubs
One way to renew large, overgrown shrubs is to cut them back over a three-year period. Begin by removing one-third of the large, old stems at ground level in late winter (March or early April). The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of the new shoots. Retain several well-spaced, vigorous shoots and remove all the others. Finally, remove all of the remaining old growth in late winter of the third year. Also, do some additional thinning of the new shoots.
A second way to renew a large, overgrown lilac is to cut the entire plant back to within 4 to 6 inches of the ground in late winter. This type of renewal pruning will induce a large number of shoots to develop during the growing season. In late winter of the following year, select and retain several strong, healthy shoots and remove all others at ground level.
Head (cut) back the tallest shoots to just above a bud to encourage branching. Large, overgrown honeysuckles, forsythias, spireas, and dogwoods can be rejuvenated in this manner. Lilacs renewed by this method may not bloom for 3 or 4 years. Pink-flowering spireas usually bloom by mid-summer of the same year.
Once overgrown shrubs have been rejuvenated, pruning should be a regular part of a home gardener's maintenance program. Most deciduous shrubs can be kept healthy and vigorous by removing a few of the oldest stems every 2 to 4 years.
Thus, cut all the way back like this, it soon grew to its large proportions with lots of blooms. While drastic, this method will greatly improve the health of an ailing bush.
Summary
- It is a good idea to remove spent flowers, to encourage flower buds for the following year.
- Remove suckers and small shoots at ground level. Leave a few shoots for new growth.
- Clean out stalks that grow straight upwards and those that crowd the inside of the bush.
- Trim back awkward branches and those which mar the shape of the overall shrub.
- That's it for regular maintenance pruning. Very old shrubs may need renewal.
Lilac Pages
Spring Blooming Shrubs How to Grow Lilacs Varieties of Lilacs
