How to Prune Lilacs

by Ken Lain, the mountain gardener

Young, immature plants rarely need pruning except to deadhead faded flowers or remove dead and broken branches. Once a lilac reaches a mature height, it appreciates rejuvenation pruning.

Young bushes with branched under three years old offer small flowers at best. Older branches, 5-8 years old, produce the most flowers. Branches older than 8 years in size should be thinned to rejuvenate your plant to younger, more vibrantly blooming branches.

When to Prune Lilac for Regular Maintenance

Lilacs are best pruned within two weeks after they finish blooming in spring. Lilacs form their spring flowers starting in summer that persist through winter for next spring blooms. Pruning other than late spring reduces next spring's flowers. The shrub tolerates pruning almost any time of the year, but if you want better color, it is best to prune right after their spring flush.

STEP 1 Deadhead Faded Flowers from Your Lilac Bushes

Removing all shriveled blooms as they fade. To do so, find the first pair of leaves beneath a faded flower cluster and snip just above those leaves.

STEP 2 Remove Dead, Broken, Bug Infested, or Canes that Rub

Remove canes that appear damaged or infested with pests, such as the lilac borer. Borers appear as small holes at the bases of shoots, accompanied by sawdust. Where two canes are rubbing together, remove the weakest to prevent damage to the more vital branch.

STEP 3 Rejuvenate Your Bush by Prune 1/3 of Its Old Canes

Mature bushes over 8 years old require rejuvenation pruning. Prune 1/3 of the oldest, largest branches back to the bush's base. This may require a pruning saw or bypass pruners.

STEP 4 Remove all suckers

Remove all shoots or suckers growing from the base or your lilac bush.

STEP 5 Rejuvenate Old Plants over 3 Years

Mature bushes over 8 years old need a 3-year rejuvenation periodically.

Remove another third of the old canes during the following spring, and repeat the process during the third spring season. Once all of the oldest growth has been cut out, allow the shrub to grow unchecked for 3 years, after which point you should repeat this rejuvenation process.

Best Plant Food for Better Flowers

Feed 4x Times per Year with 7-4-4 All Purpose Plant Food, Soil Sulfur, or Humic. Here's the recommendation by season:

Spring = 7-4-4 All Purpose Food + Soil Sulfur

Summer = 7-4-4 All Purpose Food + Humic

September = 7-4-4 All Purpose Food

December = 7-4-4 All Purpose Food

Lilac Jelly – If you want a fun canning project in spring try Lisa's Lilac Jelly Recipe.

Ken Lain can be found Throughout the week at Watters Garden Center, 1815 Iron Springs Rd in Prescott, or contacted through his websites at WattersGardenCenter.com or Top10Flowers.com.