Flower bulbs, Gardening tips, Plants,

Prune lilacs like a pro! A step-by-step guide

Lilacs are stunningly beautiful butterfly-attractors! But if you don't cut them back, they get leggy and dull. Find out how to hard-prune your lilacs for excellent results.

6 MIN 17 Jul
Last update: 17 Jul 2023
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Lilacs are stunning blooming plants that attract countless butterflies and bees into your garden, making them a staunch favourite of many garden lovers. Their beautiful bud-like blooms fill your outdoor space with an exotic fragrance, bringing gorgeous colour into your garden. But how do you prune lilacs? 

Table of contents:
  • The different varieties of lilac
  • Planting and caring for summer lilacs
  • Prune lilacs like a pro! 
  • Pruning lilacs — a step-by-step guide
  • The advantages of buddleia pruning
  • When to prune your summer lilac
  • How much should I cut?
  • Common mistakes to avoid when pruning lilacs
  • Pruning lilac — aftercare
  • Pruning your lilac is worth it!
  • FAQs

Pruning is one of the most essential garden tasks, encouraging bountiful blooming and healthy growth. But do it wrong, and you weaken your plants. 

This article explains how to prune lilac and buddleia plants to encourage healthy, vitality, and abundant flowers and foliage. 

Ready? Let’s get started!

The different varieties of lilac

Summer lilac head
A summer lilac

Common lilac blooms in spring, while summer lilac (aka buddleia) bursts into flower during the summer — both belonging to the olive plant family. 

A beautiful butterfly lilac
Butterfly lilac

There are several sub-varieties of lilacs and buddleia, including:

  • Buddleia davidii
  • Buddleia alternifolia
  • Buddleia globosa
  • Buddleia x weyeriana
  • Buddleia asiatica

Each variety has variations in colour, height, and site requirements. However, they all have one thing in common: butterflies and insects flock to lilacs of all varieties. 

Garden doctor Louis says:

The terms “summer lilac” and buddleia are often used interchangeably. However, there are several varieties of buddleia — some of which grow like weeds in walls and scrubland.

Planting and caring for summer lilacs

A single bee feeding on a lilac bush
Lilacs attract bees and butterflies – Image by Gabriele Lässer from Pixabay

Most lilacs, including the stunning Butterfly lilac (aka Buddleia Grand Cascade), like it sunny. So, choose a location away from shade when planting. Most lilacs need at least an hour of direct sun every day. 

Lilacs prefer well-draining soil — heavy clay soil becomes easily waterlogged, so add some soil improver before planting to prevent soil flooding, which will damage your lilac’s roots. 

Additionally, include a slow-release fertiliser in your planting hole and re-feed every spring to help boost your lilac’s growth. And while older lilac plants are relatively drought-tolerant, younger plants need plenty of water — hydrate potted lilacs once or twice a week. 

Prune lilacs like a pro! 

A gloved hand cutting a lilac
Use clean, sharp tools and wear protective gloves to cut your lilac!

You can be pretty brutal with a buddleia because they regrow vigorously in no time. Pruning back hard helps the plant form new flowering panicles, so cut back your summer lilac once a year, just before spring. 

Pruning lilacs — a step-by-step guide

Gather your courage if this is the first time you’ve pruned your lilac bush because you’re going to cut it back short! 

Follow these instructions for excellent results:

  1. Cutting shoots — cut the shoots down to the base of the trunk until the plant has just two short branches remaining. The cut side of each clipping should face outwards. 
  2. Dead-head regularly— remove faded panicles during the flowering season. This helps the plant develop more blooms. 
  3. Clean up — throw your cuttings into the compost or your green bin. 

The advantages of buddleia pruning

New buds growing on a hard-pruned lilac
New growth after hard-pruning a lilac

You might think that cutting a plant back so drastically is bad for the plant — but, on the contrary, your plant will flourish after hard pruning. 

You’ll enjoy:

  • More flowers — cutting stimulates the plant to form new shoots (and thus more flowers). If you skip a pruning, your plant will produce fewer flowers, and the shrub may look a little sorry for itself. 
  • Improved growth — a well-trimmed buddleia grows compactly and densely. Pruning creates an attractive shape and appearance. 
  • Rejuvenation — annually pruning your buddleia lilac gives the plant a longer life. You’ll cut off old, dead, and diseased wood and shoots, helping the plant maintain maximum health and vitality. 

When to prune your summer lilac

The best time to prune lilac is in late winter before it sprouts for spring. As a rule, the optimal period is between the end of February and the beginning of March, but it depends on whether the winter has been cold. At this point, the plant is still in its winter dormancy, and the wounds caused by pruning heal quickly before new growth kicks in. 

And dead-head your lilac throughout the summer for maximum flowers and foliage. 

Garden doctor Louis says:

Avoid pruning a lilac in autumn, as this makes your plants more susceptible to frost damage.

How much should I cut?

Reducing a plant to a few stubs sticking out of the ground may feel a little destructive, but it’s exactly what a summer lilac needs for good growth. 

Leave young plants a little longer, but don’t be afraid of hard-pruning established plants. New shoots will appear once spring settles in. 

Common mistakes to avoid when pruning lilacs

  • Always use clean, sharp tools to prune your lilac. Using blunt or dirty scissors or secateurs can transmit diseases to the plant. 
  • Avoid pruning in the autumn — the plant won’t recover in time for the frost.
  • Pruning young plants too hard. Give them a couple of years to establish before hard-pruning. 

Pruning lilac — aftercare

While pruning encourages new growth, it’s a good idea to feed the plant and water it well after cutting it back. 

Use an organic slow-release fertiliser, such as compost or blood and bone, to provide the plant with plenty of nitrogen for new growth. 

Pruning your lilac is worth it!

Pruning allows you to remove the dead and diseased shoots, which — in turn — protects the plants from pests and diseases, promoting vital growth for the flowering season.m 

Annual pruning keeps all lilac plants healthy and prolifically in bloom. And blooming lilacs attract tons of butterflies and other beneficial pollinating insects to your garden. 

Keep watering and fertilising your lilacs at least once a year to promote growth and flowering, and always use clean tools to cut your lilac back.


Should I dead-head lilacs and buddleia?

Yes. Carefully remove faded flower heads all year round — even in summer. This process, called “cleaning out, ” helps the plant focus its energy on new bloom growth. 

Should I cut butterfly lilac differently from summer lilac?

No — the pruning technique for both lilac plants is similar. However, summer lilac grows faster in summer, so that it will grow back more quickly. Remove faded blooms for new flowering heads. 

How often should I prune a lilac or buddleia?

Prune your lilacs in late winter/early summer to promote spring growth and summer flowering. Use pruning to manage the size and spread of the plant — they often grow enormous.

Any questions?

I hope I’ve provided all your questions about pruning your lilacs for excellent growth and flowering. But if you have any more questions, don’t hesitate to email me.

Or you could check out our comprehensive Help & Advice section for all your gardening and lawn care tips! 

Thanks for reading!  

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