When to Prune Lilac Bushes?

Pruning at the right time encourages lush blossoms.

The fragrant flower clusters of the lilac bush make it an attractive addition to the spring garden. With proper pruning the lilacs retain their shape and flower their fullest year after year. Pruning must be done at the proper time to ensure the plant remains healthy. Pruning at the wrong time can damage the plant or inhibit flowering the following year.

Pruning Supplies

The proper equipment ensures your lilacs are trimmed with a minimum of damage to the plants or yourself. Use sharp pruning shears. You may also need a pruning saw depending on the thickness of the lilac trunks. Wash the pruning equipment in a solution of one part bleach to nine parts water both before and after you finish pruning. The bleach solution kills any disease organisms so they aren't spread to healthy plants. If you prune diseased wood from a lilac, rinse the tools in the bleach solution before you resume pruning. Wear heavy gloves and goggles to prevent injuries.

Winter Pruning

Also known as rejuvenation pruning, trimming the lilacs while they are dormant in midwinter helps bring overgrown plants under control. Cut out up to a third of the largest, oldest stems so only six to 12 stems remain on each bush. Prune out these old stems at ground level. This type of pruning is done over the course of three years until all the old stems are removed. Leave new stems in place unless they are also overgrown. Lilacs bloom on three-year old wood, so removing the new stems means you won't have sufficiently aged plants for flowering in three years.

Summer Pruning

If your lilacs aren't overgrown, summer pruning keeps them in shape from year to year. Prune within two weeks of the completion of flowering. Waiting until too late in summer can cause you to cut off next year's flower buds. Cut back the lilacs as desired to maintain the shape and size of the plant, removing up to a third of the plants height and width. Trim off the old flowers, as this improves the appearance of the bush.

Maintenance Pruning

Maintenance pruning is done as needed, regardless of the time of year. Remove wind or storm damaged branches, especially those that don't break off completely. A clean cut from pruning shears attracts less chance of pest or disease than a broken, torn cut from a storm. Also prune out any branches that are rubbing together, as these will eventually damage each other.

References

• University of Nebraska; Lilacs -- Selection and Pruning
• North Carolina Extension; Pruning Lilacs; Dick Bir; November 2000