When Is it Best to Prune Lilac Bushes?

Lilacs flower during the early spring.

Lilac bushes are a highly-scented ornamental perennial shrub that flowers in the early spring. Pruning is generally performed after flowering for these shrubs is finished. There are two types of pruning techniques which shape the lilac bushes: heading and thinning. Both pruning techniques remove damaged or dead shrub parts and encourage new growth. Angled pruning cuts promote branch healing, and the healthy buds determine the direction of the new growth.

Summer Pruning

Lilac bush pruning generally takes place during the summer months of June and July, once the bush stops producing flowers. Pruning at this time controls the shape and size of the bushes, as well as encourages flower growth during the next growing season. Hand shears such as lopping shears will remove branches up to 1 1/2 inches in diameter. Pruning saws are best for removing main branches larger than 1 1/2 inches in diameter.

Heading

Heading of a lilac bush entails cutting back the branches at an angle to about 1/4 inch above a healthy bud. The cut is made on an angle to promote healing of the pruned branch. The topmost bud should point in the desired direction in which the new growth should appear. If the pruned branch has two buds, one should be lopped off to prevent the branch from growing forks.

Ground Level Thinning

Thinning the lilac bush to ground level removes shoots, suckers and branches back to the ground to promote an even appearance. The thinning process also strengthens the lilac bush because it removes the weakest parts which drain nutrients from the main lilac bush. Thinning can promote an aesthetically pleasing lilac bush shaped like a wide-mouthed vase flaring outward with no obvious pruning stumps.

Trunk/Branch Thinning

Thinning the lilac bush to a main branch or trunk removes weaker shoots and branches that clog the bush and obfuscate the desired shape. This pruning technique makes the trunk much more prominent, with strong, raised branches that point outward from the trunk. The lilac bush has a more tree-like appearance, with the canopy in the shape of a budding tulip. There are more noticeable main branches which will highlight the next growing season's lilac blossoms.

References

• University of Missouri Cooperative Extension; Pruning Ornamental Shrubs; Christopher J. Starbuck; 2007
• Virginia State University Cooperative Extension; A Guide to Successful Pruning, Shrub Pruning Calendar; Bonnie Lee Appleton et al; 2009