When to prune common lilac and keep it flowering

Prune a common lilac for shape just after flowering. That gives you a chance to remove selected branches before most of next season's flower buds form. Deal with a dry or broken branch separately and renew an old, crowded shrub a little at a time. Start by deciding which branch actually needs to go and what will be left when you remove it.

When to prune lilac and keep its flowers

Common lilac, Syringa vulgaris, flowers from buds made during the previous season. If you clip every tip in autumn or early spring, you can cut away much of the next display. For routine shaping, choose a time soon after flowering. Watch the shrub to see when this happens instead of counting from a date on the calendar.

A lilac in a sunny, sheltered Ukrainian courtyard may finish flowering ahead of one in a cooler or more exposed part of the garden. Warm spring days can alternate with cold spells. Inspect several sides of the shrub, especially if flowers have browned on one side and are still fresh on the other. The guide to lilac flowering helps you compare the stages. Different species and cultivars can finish at different times, so judge each plant separately.

Separate shaping from removing damaged wood

If wind has cracked a branch and left it over a path or across a gate, put safety first. Keep people out of the area beneath it and see whether the damage can be reached from the ground. Ask a professional to handle a heavy limb, a high crown or anything near utility wires. If there is no immediate risk, mark dead wood for removal during a routine inspection.

If a live branch is growing in an awkward direction but causes no problem today, mark it and wait until after flowering. When a shrub has grown across a path, find the branch that blocks access instead of clipping the entire edge. Before removing the thickest stem, see which younger ones will remain and how large a gap you would leave in the crown.

How to prune lilac after flowering

1. Step back and look from two sides. Choose an aim, such as clearing a path, stopping rubbing or making room for young shoots.
2. Follow the selected branch to its origin. Check which small branches will go with it.
3. Remove it near its point of attachment. If there is a raised collar on the supporting stem, cut just beyond it without leaving a long stub.
4. After each large cut, stop and check the outline and access to the path again.

When you only want to remove a faded flower cluster, cut at the base of the cluster above the uppermost leaves. Keep the green side shoots. On a small shrub this tidies the old flowers without changing its shape. On a large lilac there is no need to take off every faded cluster. The shrub can flower in later years without this step.

Use sharp, clean pruners on thin stems. Switch tools if the blades crush the branch instead of cutting it cleanly. If you need a saw and the limb might fall onto somebody or pull other branches with it, do not try to handle the work alone from a ladder. Inspect each lilac individually. Clean the tool after working on suspicious wood and before moving to a healthy shrub.

Example: keeping a screen beside a path

Suppose a lilac has spread across the entry path and also gives the yard privacy. Look at it from the path and from the house. Trace the one branch actually narrowing the passage and look at what will remain behind it. If it is sound and can wait, come back after flowering. Once it is removed, check the path and screen again. Save a note or a picture taken from a safe spot for comparison next spring. You can then see which branches still flower before deciding whether another cut is needed.

Renew an old shrub while keeping some bloom

On a lilac with several stems, select one or a few of the oldest that crowd the centre, obstruct a path or carry little healthy side growth. Look for a strong young stem nearby and see whether it will have room. After bloom, take out part of the old wood. Keep the other stems to retain the framework and some flowering branches. Next season, check how the replacements have developed before continuing.

Some old stems are easier to examine when the shrub is dormant and the leaves are gone. If you decide to remove them before bloom, allow for losing the buds on those branches. Cutting all stems back can postpone flowering for more than one season. It is not an annual trim. Take particular care with a weak, newly moved, waterlogged or grafted shrub.

Decide which new shoots belong to the lilac you want to keep

A well placed basal shoot on an own-root lilac may replace an old stem. On a grafted plant, a shoot from below the graft can belong to the rootstock and lack the characteristics of your cultivar. Find where the shoot originates before thinning. If you cannot identify the graft union, keep the healthy top rather than assuming the new shoots will preserve the cultivar. The guide to propagating lilac explains why the origin of the shoot matters.

When watching the shrub is enough

If a lilac did not flower, consider its age, how much light it receives and whether its tips were cut in late summer or autumn. A young shrub without flowers does not automatically need a stronger cut or fertilizer. On an older healthy lilac, mark the stems you kept and watch where flowers open the following spring. That helps you choose the next part to renew.

Base watering and feeding on the root zone and growth. The number of cuts is not a guide. If regrowth is weak, look at sunlight, moisture and the soil first. An established shrub with a separately confirmed nutrient need may benefit from an appropriate feed. Keep fertilizer away from fresh cuts.

When lilac may benefit from feeding

Complex fertilizer universal granular

For an established lilac in active growth with a confirmed nutrient need, consider this DÜNGER universal granular fertilizer. The value below is the label rate for deciduous trees and shrubs. Read the full directions for applying the product in the root zone.

Pack sizes are 3, 4 and 5 kg. Before buying, measure the area you intend to treat and check the pack sizes and prices on the product page.

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