Lilac: when and how to prune

Lilac: when to prune it?

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Prune straight after flowering, in late May or June, as soon as the flower heads turn brown. The shrub then has all summer to make new shoots with flower buds.

From July next year’s flower buds are forming: stop pruning, and certainly don’t prune in autumn, winter or early spring.

Remove suckers as soon as you see them, for instance as early as April: the younger they are, the more easily they come away.

What else to prune in those months? May · June

Lilac: how to prune it?

1. Cut each faded flower head off just above the first pair of buds or leaves below it. Don’t cut lower: those buds produce the shoots that will flower next year.
2. Every few years, saw one or two of the oldest, thickest stems off close to the ground. This lets light into the shrub and young stems grow in their place.
3. Remove dead, diseased and crossing stems. Cut young shoots with black, wilted tips, caused by bacterial blight, back to healthy wood; then disinfect your secateurs.
4. Dig out suckers with a spade, as close to the root as possible. On a grafted lilac they come from the rootstock and flower differently: so always remove them.
5. Rejuvenate an old, bare lilac over three years: each year after flowering, cut a third of the oldest stems down to the ground. That way something is always in flower.
6. Cutting stems for the vase counts as pruning too: do it in the morning, when the flower head is half open, and strip off most of the leaves.

How much to cut, and how often?

• Every year after flowering, the faded flower heads and the suckers, and every two to three years one or two old stems as well.
• Never remove more than a third of the shrub at once: even a neglected lilac is better rejuvenated over three years than in one go.
• On a large, tall lilac, deadheading every flower head is a hopeless task: cut what you can reach. The most important job is removing old stems and suckers.

What does it mean for wildlife?

• Lilac is a favourite nesting site for blackbirds, song thrushes and dunnocks. The May–June prune falls right in the nesting season (15 March–15 August): check carefully between the stems first, as disturbing an active nest is against the law. If there is a nest, only cut the flower heads you can reach without disturbing it.
• In May the fragrant flowers attract butterflies such as the brimstone and the small white, and long-tongued bumblebees; the hummingbird hawk-moth sometimes visits too. So only cut off the flower heads once they have really finished.
• The caterpillars of the lilac leaf miner tunnel into the leaves in summer. The shrub hardly suffers: there is no need to spray, at most remove the worst leaves.
• Old stems can go on a dead hedge or serve as deadwood in a corner of the garden: shelter for hedgehogs, wrens, beetles and solitary bees.

Common mistakes

• Pruning in winter or early spring, so that year’s flower buds are gone.
• Cutting faded flower heads off too low, taking next year’s buds with them.
• Leaving suckers until the shrub spreads across the whole border or the rootstock takes over.
• Cutting an old lilac down to the ground in one go, so it barely flowers for years.
• Pruning in June without checking for nests first.

Nearby: related pruning guides

• Meyer lilac
• Hungarian lilac
• Persian lilac
• Forsythia
• Mock orange

Similar to: Difference from Californian lilac · Difference from Indian bean tree

Plant profile: Lilac · Pruning calendar and basic rules