The best time to prune lilac is straight after it finishes flowering, which in Essex is usually late May to mid-June. Lilac sets next year’s flower buds over summer, so pruning in autumn, winter or early spring cuts off the following spring’s blooms. The one exception is hard renovation of an overgrown lilac, which can be done in late winter if you accept a year or two with fewer flowers.
When is the best time to prune lilac?
The best time to prune lilac (Syringa) is immediately after flowering, within a few weeks of the last blooms fading. For most common lilacs in Essex gardens, that means late May to mid-June.
Timing matters because lilac flowers on wood made the previous year. Soon after flowering, the shrub starts forming the buds that will open the following spring. Prune straight away and those buds develop as normal on the new growth. Leave it until later in the year and every cut removes flowers you would otherwise have enjoyed.
Why shouldn’t you prune lilac in autumn or winter?
You should not routinely prune lilac in autumn or winter because the flower buds for next spring are already on the stems. A tidy-up in October or February may look neat, but it can leave you with a lilac that is full of leaves and has hardly any flowers.
Pruning at the wrong time will not kill a healthy lilac. It simply costs you a season of blooms. The only reasons to cut outside the summer window are to remove dead, damaged or diseased wood, which can be done at any time, or to renovate a badly overgrown shrub.
How do you prune a lilac after flowering?
To prune a lilac after flowering, remove the faded flower heads, take out a few of the oldest stems at the base and thin any crossing or weak growth. Light, regular pruning each year keeps a lilac healthy, flowering well and at a manageable size.
- Deadhead the spent flowers. Snip off faded flower clusters just above the first pair of healthy leaves or buds below them. This keeps the shrub tidy.
- Cut out dead and damaged wood. Remove any dead, broken or diseased branches back to healthy wood.
- Remove some old stems. On an established lilac, cut one or two of the oldest, thickest stems down to near ground level. Fresh young shoots will grow to replace them and flower in future years.
- Thin crowded growth. Take out stems that cross, rub or crowd the centre so light and air can reach the middle of the shrub.
- Deal with suckers. Pull or cut away unwanted suckers from the base, keeping one or two strong ones if you want to replace an old stem.
Use clean, sharp secateurs or loppers and cut just above a bud or side shoot. Avoid taking more than about a third of the shrub in one year.
How do you prune an overgrown lilac?
You can bring an overgrown lilac back into shape in one of two ways: gradually over three years, or with a hard cut in one go. The gradual method is gentler and keeps some flowers each year, so it is the one we usually recommend.
- Gradual renovation. Straight after flowering, cut around a third of the oldest stems down to 30cm or lower. Repeat over the next two summers until the whole shrub has been renewed.
- Hard renovation. In late winter, cut all the main stems down to around 30 to 60cm. The lilac will regrow vigorously, but expect little or no flowering for one to three years.
Hard renovation suits a lilac that has become tall, leggy and bare at the base, especially once it is shading a path or window. Older grafted lilacs can respond less reliably, so it is worth asking for advice before cutting a mature shrub right back.
Do lilac trees need different pruning?
Lilacs trained as small trees on a single trunk are pruned at the same time, straight after flowering, but more lightly. Keep the main trunk clear of shoots, remove suckers from the base and thin the head of the tree just enough to keep it balanced and open.
Large, mature lilac trees close to buildings, boundaries or power lines are best left to a professional. Working at height with loppers and ladders is a common cause of garden injuries, and an experienced eye will shape the tree without spoiling next year’s flowers.
Need help with lilac or shrub pruning in Essex?
If your lilac has outgrown its space, stopped flowering or simply needs a careful prune, our team can help. Crown Tree Services offers shrub pruning in Essex alongside hedge trimming and garden and landscape maintenance, always timed to protect the health and flowering of your plants.
Our team is based in Ongar and regularly works across Essex, providing professional tree services in Romford, Hornchurch, Ongar and tree surgery services in Chelmsford.
Contact us online to get a free shrub pruning quote and we will arrange a site visit at a time that suits you, or call us on 01277 525150.
About the Author: Stephen O'Reilly
