How do you prune a lilac that has grown too big?
By Service Plus Stockholm AB4 min read
Short answer
How do you prune a lilac that has grown too big?
A lilac that has grown too big is rejuvenated by sawing a third of the thickest, oldest stems down to 10–20 cm above the ground each year for three years, right after flowering in May–June. This gives the shrub new energy to send up healthy shoots while it keeps flowering every season. A harder alternative is to saw the whole shrub down at once directly after flowering, but then it will not flower for one to two years while the lilac builds itself up again.
Would you rather have it done for you? Read about tree & shrub pruning in Stockholm – what is included, what affects the price and how to book.
Why lilacs grow so big and bushy
Lilac (Syringa) is one of the most widely grown shrubs in the Stockholm region and, left unpruned, can reach 4–5 metres in height and become just as wide. The shrub constantly sends up new suckers and stem shoots, so it easily grows dense and shady in the middle unless thinned regularly.
When a lilac becomes too big it often stops flowering in the lower parts because light no longer reaches in, and the flowers end up high up and out of reach.
Rejuvenation pruning over three years is the safest method
The gentlest method for an overgrown lilac is to spread the pruning over three seasons. This gives the shrub time to recover and keep flowering every year while it gradually shrinks to a manageable size.
- Year one: saw off a third of the thickest and oldest stems close to the ground, about 10–20 cm above the soil
- Year two: remove another third of the remaining old stems in the same way
- Year three: saw down the last third so that only healthy, young stems remain
- At the same time, thin out suckers that grow too densely or too far from the shrub
- Always cut shortly after flowering in May–June, never in autumn or winter
Hard cutting back gives faster results but no flowers for a while
A faster alternative is to saw the whole lilac down to 30–50 cm above the ground in one go, directly after flowering. This works well on healthy, vigorous shrubs but means flowering is lost wholly or partly in the first year and often the second as well.
The method is best suited when the lilac is so overgrown or damaged that gradual pruning is no longer enough, or when the space needs to be freed up quickly.
- Cut all stems to the same low height with a clean, sharp saw
- Water the shrub thoroughly during the summer after the cut
- Thin out weak new shoots the following spring so the strongest have room
- Expect full flowering again after about two to three seasons
How to care for the lilac after a major pruning
After heavy pruning a lilac often sends up many new suckers the same summer. These need thinning so that only the strongest 8–10 stems remain, otherwise the shrub will be just as dense and bushy as before within a few years.
Feed with well-rotted compost or garden fertiliser in spring to give the shrub extra energy to build new branches.
- Thin out weak and inward-growing shoots every spring
- Remove spent flower heads directly after flowering for richer flowering next year
- Avoid nitrogen-rich fertiliser in late summer, it only encourages foliage at the expense of flowers
- Check that new suckers are not spreading too far from the stem
How Service Plus helps with pruning lilacs
A large, overgrown lilac with thick, old stems can be heavy and awkward to saw down yourself, especially if the shrub stands close to the house, fences or other plants. Service Plus Stockholm AB assesses the condition of the lilac on site and provides a free quote with a clear price before work begins.
Saxa, the Service Plus pruning specialist, decides whether the lilac is best served by a three-year rejuvenation or a faster cutting back, and makes sure the pruning is done at the right time so the shrub keeps flowering for many years to come.
Common follow-up questions
When in the year should you prune a lilac?
Prune the lilac directly after flowering in May–June, because next year's flower buds are already formed during the summer and autumn.
Can you prune a lilac in autumn or winter?
You can, but then next spring's flowers are lost because the buds are already on the branches, so autumn or winter pruning only makes sense as a shaping cut if you are prepared to sacrifice one season's flowering.
How much can you remove from a lilac without killing it?
A healthy lilac tolerates a third of its stems being removed each year for three years, and can also be sawn down completely in one go, as long as the root system is healthy and the shrub is well watered afterwards.
Does pruning a lilac qualify for the RUT deduction?
Yes, the pruning work itself counts as a garden service and qualifies for the RUT deduction of up to 50% of the labour cost, but removal of brushwood and branches is not included in the deduction.
