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How to Prune Lilac: Right After Flowering

How to prune lilac: right after flowering, deadhead at the base of the flower cluster, remove one-third of the oldest stems each year, and what Bloomerang changes.

Iris BellPublished Oct 25, 2026 · Updated Oct 25, 2026 · 2 min read
Common lilac shrub with purple flower clusters
Photo: GT1976, CC BY-SA 4.0

Prune lilacs immediately after they flower: Iowa State says that is the best time and helps the lilac produce the most flowers the following spring. The reason is bud timing. Iowa State says lilacs set their flower buds for the following season in mid-summer, not long after the spring blooms fade, and Penn State says that pruning branches later in the year will remove future flowers. This guide sits under our lilac care guide.

Timing: why right after bloom

Right after flowering

Iowa State says this is the best time to prune lilacs and will help them produce the most flowers the following spring.

Later in the year

Penn State says flower buds form the summer before they bloom, so pruning branches later in the year removes future flowers.

Late winter

Iowa State says some blooms will be sacrificed, but larger branches are often not as floriferous, and it is much easier to see and remove branches while the plant is dormant.

Late winter is the trade-off option: you lose some flowers, but you can see the branch structure.

Deadheading

Iowa State says that when deadheading lilacs, you should make the pruning cut at the base of the flower cluster and just above the uppermost leaves. It adds that lilacs that are promptly deadheaded after flowering often bloom more heavily the following season than those that are not.

How much to remove

Every year (Penn State)

Remove one-third of the oldest stems. Penn State says this prevents your plant from becoming tall and leggy.

Every 3 to 5 years (Iowa State)

Remove the oldest and largest branches within 6 to 8 inches of the base. This can also reduce the overall size of the shrub and promote new growth that blooms better than older stems.

The two sources give different cycles: a steady one-third each year, or a larger cut every 3 to 5 years. Either keeps the focus on the oldest wood.

  1. Deadhead right after the bloom fades. Cut at the base of the flower cluster, above the uppermost leaves (Iowa State).
  2. Pick out the oldest stems. They are the targets for renewal (Penn State, Iowa State).
  3. Remove about one-third of the oldest stems. Penn State’s yearly rule.
  4. Or take the oldest, largest branches to 6 to 8 inches. Iowa State’s 3-to-5-year option.
  5. Dip pruners in alcohol between cuts. Penn State says this avoids spreading infection.

Bloomerang lilacs

NC State says Bloomerang lilacs bloom on both old and new wood. If pruning is necessary, NC State says to do so immediately after the first bloom in early spring.

Mistakes to avoid

TimingPruning after buds setBranches cut later in the year carry the next season’s flower buds (Penn State).HygieneSpreading infectionPenn State says to dip pruners in an alcohol solution between each cut.

For sun, spacing and problems like powdery mildew, see the lilac care guide. The same rule applies to forsythia.

Frequently asked questions

When is the best time to prune lilacs?

Iowa State says immediately after flowering is the best time and helps the lilac produce the most flowers the following spring.

What happens if I prune lilacs in late winter?

Iowa State says some blooms will be sacrificed, but it is much easier to see and remove the branches when the plant is dormant and without leaves.

How do I deadhead a lilac?

Iowa State says to make the pruning cut at the base of the flower cluster and just above the uppermost leaves. Lilacs that are promptly deadheaded often bloom more heavily the following season.

How do I renovate an overgrown lilac?

Penn State says removing one-third of the oldest stems each year prevents a tall, leggy plant. Iowa State says removing the oldest and largest branches within 6 to 8 inches of the base every 3 to 5 years reduces the shrub's size and promotes new growth.

Are Bloomerang lilacs pruned differently?

NC State says Bloomerang lilacs bloom on both old and new wood. If pruning is necessary, do it immediately after the first bloom in early spring.

Sources

  1. Growing Lilacs in the Home Garden, Iowa State University Extension and Outreach
  2. Lilac Care, Penn State Extension
  3. Syringa Bloomerang Group, NC State Extension Plant Toolbox