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Best time to prune lilac bush


Russell Tree Experts — When and How to Prune Lilacs

Please note: This article was originally published on 4/6/2020 and was republished on 6/9/2021.

Common lilacs (Syringa vulgaris) are a favorite landscape shrub here in Ohio and beyond, with flowers that provide beauty and an unmistakable fragrance every spring. Other cultivars of lilacs offer different habits and uses in the landscape, but provide the same display of flowers that we all love. In order to ensure you get the most flowers on your lilac year after year, it’s important to know when and how to prune them.

When To Prune

As a general rule for all lilacs, they should be pruned immediately after they’re done flowering in the spring. Since lilacs set next year’s flower buds right after the current year’s flowers have faded, pruning later in the summer or fall will result in cutting off many or all of next year’s flowers. This rule of timing applies to the larger common lilacs as well as the cultivars that are shorter or more “shrub” like. While the “when” of pruning lilacs is fairly straightforward, the “how” gets a little trickier. To keep things simple for now, we’ll think of lilac pruning as either maintenance pruning or rejuvenation pruning.

How To: Maintenance Pruning

For any lilac shrubs that have not outgrown their space or are still producing vibrant flowers each year, regular pruning can simply consist of any shaping that you choose to do along with removal of dead, diseased, or broken stems. You can also remove spent flowers from your lilacs to help encourage a cleaner growth habit and appearance. It’s always better to do this type of pruning by hand, rather than shearing. When making cuts, try to cut back to an outward facing bud. A good pair of hand pruners is the perfect tool for this and makes for much better pruning cuts than hedge shears.

How To: Rejuvenation Pruning

If you’ve ever had an older common lilac in your landscape that went unpruned for many years, you’re probably familiar with their overgrown, unruly habit when left alone. Many people mistakenly believe that these shrubs have stopped flowering at this point. Oftentimes what’s actually happening is the flowers are being produced on just the upper portions of the shrub where the plant has reached a taller height and is exposed to sunlight. Once they’ve reached this stage, we’re often left to stare at bare, woody branches at eye level and below. For these overgrown shrubs, we can remove entire older canes or stems that are 2” in diameter or larger to encourage a rejuvenation of the shrub. We want to apply the rule of thirds when doing this type of pruning - Remove approximately one third of the older canes or stems each year for 3 years. This gives the shrub a chance to slowly transition back to a fuller, shorter shrub with more new growth filling in from the bottom. If you decide to drastically prune the entire shrub this way all at once rather than just a third of it, a little extra care like fertilization and watering will be important to encourage new growth. Note that this “all at once” approach is generally not recommended for the health of the shrub.

Your lilac flowers can be influenced by many things, including the temperature, soil conditions, even disease and insect problems, but proper pruning goes a long way to ensuring they put on a great show every spring. And remember, if you have specific questions about pruning or anything tree and shrub related, your dedicated Russell Tree Experts arborist is only an email or phone call away.

*New* Video!


To accompany the above article, Walter Reins demos how to prune lilac trees in this new video! Click below!

How to Prune Lilac Bushes

The Spruce / Steven Merkel

Regular Maintenance Pruning

How far you can cut back a lilac bush follows the general shrub pruning rule: Cut no more than a third of the stems each year, starting with the oldest. That will help the plant remain constantly vital, with new stems developing as old stems bloom. Your goal for a lilac pruning diagram is to have a bush with somewhere between 10 and 12 stems, all of them between 1 and 2 inches in diameter.

  1. Prune Unsightly Features

    Begin by pruning dead or diseased stems, pencil-thin suckers that are far from the bush, and twiggy growth. Cut these back all the way to ground level. Pruning shears or loppers will generally handle these stems.

    The Spruce / Steven Merkel

  2. Remove Any Stems Thicker Than 2 Inches in Diameter

    This regular removal of entire old stems will prevent your lilac from becoming too tall. Avoid cutting off just the tops of long stems because this can leave the plant with an odd, unnatural shape. With very large stems, a pruning saw might be necessary. Thick lilac stems can be very tough.

    The Spruce / Steven Merkel

  3. Trim Remaining New Stems

    If you want your lilac to fill in more and become shrubbier, trim the remaining new stems to an outward-facing bud. This means pruning just beyond buds that face away from the center of the plant. This technique will cause more branching and create a denser shrub.

    The Spruce / Steven Merkel

Rejuvenation Pruning

Older lilacs can have stems as thick as small trees and will flower only on the topmost branches. Fortunately, rejuvenation pruning can revive an old lilac in about three years' time. There are two approaches you can take.

The less drastic approach to getting an overgrown lilac back into shape is to use the "third" rule. Prune a third of the oldest branches all the way to the ground each year for three consecutive years. Start by taking out the thickest stems first. Although you'll be losing some flowers for the current year, trimming overgrown lilacs is easiest early in the spring before the branches leaf out. After three consecutive years of pruning your overgrown lilac in this way, new shoots should comprise the bulk of the plant. The plant will begin to bloom all over, and you can do regular maintenance trimming from that point on.

If you can't stand the look of your old lilac or you just want a quicker approach, you can take the drastic measure of cutting back the entire plant to about 6 to 8 inches above the ground in the early spring. Fertilize the plant with compost or a balanced fertilizer to prompt new growth. New shoots will develop throughout the growing season; let them grow through the summer. The following spring, begin pruning out the spindly growth, and maintain the healthiest shoots while considering the shape of the plant. Encourage branching by cutting back the remaining shoots to just above a bud. Carry on with regular maintenance pruning after this.

Working With Japanese Lilac Trees

The Japanese lilac tree (Syringa reticulata) is a plant that can grow as high as 30 feet and has become increasingly popular in urban environments. It has a vase-shaped crown with spreading branches, and it produces showy white flowers in June.

Consistent with their tree-like shape, these plants should be pruned in the same manner that most small trees are handled. Prune to maintain an open interior and several main branches that form a vase shape. Lilac trees generally require little, if any, pruning until they are a few years old.

After this, any necessary pruning should be done immediately after the flowering period is over. Remove dead or diseased branches, as well as any branches that interfere with the overall vase shape or clutter the interior of the tree. If the lilac tree grows too tall, you can cut back individual branches to around 1 foot below the desired height to prompt dense growth at the top.

Tips for Pruning Lilacs

Dwarf lilacs, such as ‘Palibin’ Meyer lilac (Syringa meyeri ‘Palibin’) and ‘Miss Kim’ Manchurian lilac (Syringa pubescens ssp. patula ‘Miss Kim’), look similar to the common lilac. However, how to prune these lilac bushes differs. They rarely require maintenance pruning, though you can trim when necessary for shape.

Like other lilac varieties, they also can benefit from deadheading. Deadheading is the practice of removing dead blooms from a plant by hand. With some plants, this helps to stimulate continuing blooms.

New lilac plants should begin blooming within two to five years. Deadheading the spent flowers will encourage new bud development for the next spring. However, once the plant has matured, it won't need this encouragement, and you'll likely have so many flowers that the task would be too time-consuming.

As with any plant, some years your lilac will bloom magnificently and some years not so much. Blooms are often dependent on the weather. A pleasant summer during which healthy new growth develops will reward you with abundant blooms the following year. A summer with extreme weather will yield fewer flowers. So don't panic if your lilac isn't as vibrant from one year to the next. As long as the plant is healthy and you keep up with maintenance pruning, the flowers will follow.

How to Grow and Care for Lilac Bushes

Lilac pruning - types and rules.

Photo — Botanichka

Lilac is one of the most beloved plants in our gardens. However, in order for it to be luxurious, it needs proper care. And here the question is not only in choosing a place and landing, but also in the correct pruning. It is believed that in order for the lilac bush to bloom well, it must be “broken”. However, this understanding is only part of the truth.

Lilac pruning - types and rules

In fact, lilac requires both sanitary, and shaping, and stimulating and even flowering pruning. And at the same time, they must be produced in the right time frame, with an understanding of what you are doing and a vision of the end goal. Simply breaking lilac branches stresses the plant, increases the risk of developing fungal diseases and stimulates its aging. Let's look at the rules for pruning this wonderful shrub, especially since they are simple. nine0003

Early spring sanitary pruning of lilacs

Sanitary pruning of lilacs is recommended to be done in two terms. The first - in early spring, before the dissolution of the kidneys - in March-April. The second - at the end of flowering. It consists in:

However, if you did not sanitary pruning in the early spring, it does not matter. It can also be done after flowering, along with shaping pruning.

Early spring pruning to control lilac bloom

Many plants have a feature - if they gave a great harvest this year, they will rest next year. The same principle applies to lilacs. If this year it bloomed especially abundantly, the next flowering will be more scarce or weak. To prevent this from happening, lilac bloom must be regulated.

This should be done in early spring, at the same time as sanitary pruning. It is necessary to remove part of the shoots with flower buds, leaving only the strongest ones. nine0003

Pruning during lilac blossom

Yes, yes, pruning. You can cut flowering lilac twigs just for a bouquet, or you can in order to stimulate the laying of flower buds. It is to cut off with secateurs, and not break off - mechanical injuries - the place of penetration of fungal spores, which means the spread of diseases. But there is one rule: you need to cut off no more than half of the flowering shoots.

Why not more than half? You must have seen bushes that break off badly every year. Such plants lay a large number of new buds, branch strongly, their inflorescences are crushed, the crown of the bush thickens greatly, the plant loses its attractiveness, looks exhausted. nine0003

When cutting a lilac branch for a bouquet, cut it to a sufficient length, preferably at the base, leaving no stumps. This will enable the plant to form more harmoniously.

Pruning during flowering

Lilac summer shaping pruning

Lilac shaping pruning can only be done in summer, after flowering. This is an important rule, because if you correct the shape of the bush in the spring - remove its height or reduce the radius of the crown, along with the tips of the branches, you will remove flower buds, as a result of which flowering will be scarce, and even absent with intensive pruning. nine0003

Do not postpone this pruning until the end of summer - autumn. In this case, the lilac will also not bloom the next year or will be able to form flower buds only on separate shoots.

Summer pruning of the formation necessarily includes both sanitary pruning, especially if it was not done in the spring, and rejuvenating pruning. In general, it includes:

And if the faded inflorescences are not cut off? In this case, the bush expends energy on the ripening of fruits, as a result, it lays flower buds less intensively and, as a result, blooms poorly in the next season.

Some people regret cutting out the growth, thinking that a large bush will bloom more luxuriantly. This opinion is wrong. Excess basal shoots increase the size of the bush, worsening its appearance. Inflorescences on such plants are formed smaller. The shading of the crown increases, the ventilation of the bush worsens, increasing the risk of developing diseases. In addition, excess growth depletes the plant, as it takes food and moisture from it. nine0003

Lilac rejuvenation pruning

This type of pruning is done exclusively on mature plants. The need for it appears if the lilac bush has become old and has ceased to give a full-fledged growth. In this case, the old branches must be removed completely, at the base, if the plant is rooted. Or above the grafting site if the plant is grafted. In a few years, young growth will rise up and replace them.

However, it is not recommended to remove all old branches at once. Rejuvenation must be done in stages, removing no more than 2 branches per year. In this case, it will be easier for the plant, and the decorative effect will be preserved. nine0003

Cuts on thick branches should be done at a slight angle so that moisture flows freely from them, otherwise the wood will decay more quickly. Clean with a knife and process with garden pitch or garden paint. This technique reduces the risk of infection.

If the grafted plant is pruned “on a stump”, which is left 40-60 cm high, several new shoots may form at once above the cut point next year. Of these, it is necessary to leave 2–3 of the strongest, well-located, cut the rest “into a ring”. Already in the third year, the lilac will recover and bloom. nine0003 When the lilac has finished flowering, cut off the old inflorescences above a well-developed pair of leaves

General rules for pruning lilacs

When starting to prune lilacs, it is necessary to remember that our task is to help the tree form and reach its potential. Therefore, do not neglect the rules and apply them all. The most difficult thing for beginner gardeners is rejuvenating their plants and thinning the crown. But without these techniques, the lilac thickens, loses its decorative effect, and over the years begins to disappoint. nine0003

The second thing to keep in mind. Any pruning is a trauma for the plant. It is necessary to produce it at a certain time, with well-ground and sterilized garden tools, so as not to leave torn edges on the cuts and not to infect the wounds. After pruning, treat large cuts and saw cuts with garden pitch or garden paint. Update the garden variety as needed.

When pruning lilac, you need to focus on the fact that no more than 20% of the crown can be removed from the plant at a time, otherwise it will begin to intensively grow new shoots, which will lead to its thickening. After pruning, it is important to support the plant - after a couple of days, make a good watering, if necessary, top dressing. If the shoots are left for the propagation of the variety, plant it in time. nine0003

And don't be afraid to experiment! The lilac grows well, and already one and a half to two months after pruning, its crown is completely restored, so if you make a mistake in something, the mistake can always be corrected.

Lilac care: pruning in detail

It is impossible to find a garden without at least one lilac bush. Every gardener wants the lilac in his garden to bloom more abundantly than others, and her inflorescences to be the most lush. Some leave the shrub unpruned, allowing it to grow up and out, and this works for a while in fertile areas. Others cut lilacs very hard, increasing the number of young shoots, and hoping to get larger inflorescences. nine0003

Frank Fujimoto / Flickr.com

It's really important to stick to timing and cutting patterns. Otherwise, the lilac runs wild and its crown thickens, the inflorescences and the diameter of the corolla of flowers in them become smaller, and flower buds are not laid on all shoots. If you cut the shrub very much, then for a while it may lose its ability to bloom. Pinching or pruning of terminal buds stimulates the growth of lateral shoots and near-stem shoots and thickens the bush.

The best time for pruning lilacs is immediately after flowering, when you can combine the removal of wilted inflorescences and crown thinning. Removing reddened lilac panicles is necessary not only from an aesthetic point of view. In lilacs, the formation of fruits and seeds competes with the development of nearby young green shoots, at the ends of which flower buds are laid. Need to remove inflorescences immediately after flowering i in June, so that nutrients are not wasted on setting seeds that have no value. Inflorescences are removed just above the nearest pair of leaves or green shoots on a branch.

K M / Flickr.com

Non-double varieties of common and broad-leaved lilacs are more prone to fruit set, so it is imperative to remove wilted inflorescences from them. These are varieties such as Red Moscow, Sensation, Lebedushka, Flora, Twilight, President Lincoln and others. Their pruning in the middle of summer or autumn will not bring the desired effect. nine0003

But varieties with semi-double and double flowers (Maximovich, Condorsier, Lavoisier, Beauty of Moscow, Lesya Ukrainka, Madame Casimir Perrier, Madame Lemoine, etc.) less often form seeds, so they can be cut throughout the summer.

Shihmei Barger 舒詩玫 / Flickr.com

In June lilac rejuvenating and shaping pruning can also be done. Lilac inflorescences form on old branches, so they cannot be completely cut out, however, the constant removal of young branches will lead to the fact that flowering on old branches will stop after some time. Therefore, young lilac bushes leave 3-4 main trunks. Old bushes are rejuvenated by cutting off more than half of the perennial shoots at the base of the bush. The remaining branches can be shortened by 30-60%. Such a lilac will not bloom next year, but after two years the size of the flowers will increase, and the flowering will be more magnificent. nine0003

Martin LaBar / Flickr.com

Thick fat shoots, curved, protruding branches thickening the crown, as well as diseased or diseased branches are cut in the crown, the symmetry of the bush is corrected. Shortening young green shoots of lilacs is not recommended. Fragrant flowers will bloom on them next year. Their upper part with 3-4 pairs of leaves can be pinched if necessary to correct the symmetry of the bush or the development of side shoots. The root shoots of lilacs are removed at any time, such shoots are cut out below the root neck. nine0003

Use a sharp pruner or scissors to prune shrubs, cut the branches at right angles. Large branches can be cut down. Sections larger than 3 cm in diameter are treated to protect the shrub from fungal infections or parasitic organisms.

Discuss video

Annual pruning of lilacs after flowering is the key to an annually blooming garden.

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