How to Prune Lilacs for More Blooms and a Bounty of Butterflies

Do You Need to Prune Lilac Bushes?

Lilac bushes are hardy flowering shrubs that bloom each spring to support butterflies and other beneficial pollinators. But alas, learning how to prune lilacs for optimal growth will take a bit of extra effort on your end…

Lilacs need proper pruning to maintain their form and flowering capabilities.

Regular pruning helps lilac bushes maintain better health, appearance and bloom production:

To keep lilacs looking their best, two types of pruning are recommended:

• Maintenance pruning involves removing spent flowers and thinning out some older stems to encourage new growth.
  
• Rejuvenation pruning is for overgrown lilacs. This involves cutting old stems to near ground level. This stimulates new shoots (suckers) to emerge, so the shrub produces blooms the following spring.

Lilacs generally respond well to pruning. Annual pruning ensures your lilac flowers will continue to bloom beautifully for years to come. Here’s what you’ll need to get started…

Tools Suggestions For Pruning

For pruning lilacs effectively, you’ll need one or more of the following tools:

• Bypass Pruners (Hand Pruners): These are essential for cutting smaller stems, typically up to 3/4 inch in diameter. Bypass pruners make a clean cut and are less likely to crush the stem, which is important for plant health.
  
• Loppers: For branches that are too thick for hand pruners (usually 3/4 inch to 1 3/4 inches in diameter), loppers provide longer handles for leverage and larger blades for cutting.
  
• Pruning Saw: For larger, older, or thicker branches (over 1 3/4 inches in diameter), a pruning saw is necessary. There are various types, including curved blade saws and folding saws.
  
• Hedge Trimmer: While these are not generally recommended for pruning lilacs, we’ve used this on our dwarf lilac bushes with great success. Using the trimmer is a big time saver too.
  
• Garden Gloves: Heavy-duty gardening gloves will protect your hands from getting scratched up by branches.
  
• Safety Goggles or Glasses: To protect your eyes from flying debris or snapping branches.
  
• Rubbing Alcohol or Disinfectant Wipes: For cleaning your tools before and after pruning to prevent the spread of diseases.
  
• Sharpening Stone or Tool Sharpener: Keeping your tools sharp makes clean cuts and reduces effort.
  
• Tarp or Drop Cloth: To collect pruned branches and make cleanup easier. (for large lilac bushes)
  
• Netting: For the lilacs towering over our water feature, we put netting over the feature so we don’t have to fish branches out of the water.
  
• Bucket or Wheelbarrow: For transporting pruned material. (for large lilacs)
  
• Hydrogen Peroxide: if you have issues with fungus on lilacs, spraying a hydrogen peroxide mix on the remaining leaves and stems can kill potential pathogens

No matter which cutting tool you choose to prune your lilacs, make sure the blades are sharp to make clean cuts and prevent disease.

Maintenance Pruning (Annual Shaping and Health)

• When to Prune Lilacs: maintenance pruning should be done in late spring or early summer. Lilacs form their flower buds for the next year very shortly after the current year’s flowers fade. If you wait too long (late summer, fall, or winter), you risk cutting off those developing flower buds, resulting in fewer or no blooms the following spring.

• Dead, Damaged, or Diseased Branches: Cut these back to their point of origin (where they connect to a larger branch or the main stem) or to healthy wood. Make sure your tools are clean and sharp to prevent disease spread.
  
• Crossing or Rubbing Branches: Remove one of the branches that are crossing or rubbing against each other. This prevents wounds that can become entry points for pests and diseases.
  
• Thinning: To improve air circulation and allow light into the center of the bush, remove some of the inner, weaker, or overcrowded branches. Cut these back to their point of origin.
  
• Shaping: For general shaping, cut back to an outward-facing bud or a side branch. This encourages the plant to grow in the direction you desire and prevents inward-growing branches that can lead to a dense, unhealthy interior. Make cuts at a 45-degree angle to prevent water from collecting on the wound.

Rejuvenation Pruning (for Overgrown or Neglected Lilacs)

• When to Prune Overgrown Lilacs: also immediately after flowering in late spring or early summer
  
• The “Rule of Thirds”: This is the most common and recommended method for heavily overgrown lilacs. Over three consecutive years (pruning after bloom each year), remove about one-third of the oldest, thickest stems right down to the ground. These oldest canes often have scaly, cracked bark and are less productive. This gradual approach allows the plant to recover and avoids shocking it, while encouraging new, vigorous growth from the base.
  
• Drastic Renovation (less common): In extreme cases, you can cut the entire plant back to within 6-12 inches of the ground in late winter/early spring. However, this will result in no blooms for 2-3 years and can lead to a flush of suckers that will need management. This method is generally not recommended unless absolutely necessary.

If you want to attract and support spring butterflies and other precious pollinators, learning how to prune lilacs will go a long way toward achieving this goal…happy pruning!