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When and how to trim a 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

How to cut lilacs.

Lilac pruning correctly. In the spring?

By Oksana Jeter 05/12/2017 Garden-decorative, In the garden, Spring in the garden, Summer in the garden, My garden in the south of England, Gardening technology 10 comments

Lilac pruning in spring? How to prune lilacs correctly

How to prune lilacs correctly, whether to prune lilacs in spring and whether lilacs can be prune at all - such questions are often asked by gardeners. Meanwhile, it is necessary to cut the lilac, otherwise the flowering of this beautiful plant will be scarce and mainly at the very top of the bush, and the lower part and middle will consist of bare lignified branches. Read our article on when and how to properly prune lilacs.

The most common type of lilac in our gardens is numerous varieties of shrubs common lilac (Syringa vulgaris) , which this article is about and which we will simply refer to as lilac .

The largest lilac inflorescences appear on branches aged 2 to 5 years. Lilac blooms only on well-ripened wood of the previous year. The older the branches become, the smaller the inflorescences and the higher they are located. At the level of human growth and gaze, the old lilac branches become stiff and bare. From these features of the lilac vegetation, it becomes clear that this plant, like no other, needs proper pruning. Old and neglected lilac bushes require strong rejuvenating pruning.

Pruning lilacs in spring…

…may not be the best idea if you expect to see blooms this year. If you have extra time, in the spring you can cut branches broken during the winter or shorten branches that do not have buds. The main formative pruning of lilac should be done immediately after flowering, approximately once every two years. This rule applies to all flowering trees and shrubs. Formative pruning immediately after flowering (June) will allow the plant to grow new shoots and form new buds by the time of the next flowering.

As for rejuvenating pruning of old lilac , it is done just in the very early spring, as soon as low positive temperatures are established in the garden (in mild climates, such pruning can be done in winter).

How to prune lilacs correctly: shaping pruning

  • shorten long branches by approx. 1/3
  • thin out the branches near the ground, cutting off excess and old branches at the root
  • cut off (or carefully remove with roots) excess basal shoots if the lilac has grown too wide

    • After finishing pruning, the lilac bush will have a compact, rounded appearance.

    How to prune old lilacs: rejuvenating pruning

    Rejuvenating pruning of old lilac bushes should be carried out as early as possible in spring (if you are not interested in flowering) or immediately after flowering (see photo diagram *, enlarged):

    After the rejuvenating pruning of the lilac, the bush will look like a lot of stump branches, but very soon new buds and greenery will form on short branches, and in a year the lilac will bloom magnificently (with good care, of course). Fragrant inflorescences are enough for cutting and for a gift to friends. Photo below: lilac in a vase.

    Pruning grafted lilacs

    Peculiarities of pruning grafted lilacs are that pruning should be done ABOVE the grafting site. All side shoots should be removed, because. flowering on it will correspond to the type and variety of the rootstock, and not the highly decorative scion that you are counting on.

    Lilac shaping and rejuvenating pruning system

    In my garden I use this system as the most practical one. In our conditions, the lilac just grows wildly, so I left 2 bushes and strictly maintain them in a compact state, 2-2.5 m, by alternating shaping and rejuvenating pruning. One year, immediately after the end of flowering, I rejuvenate bush 1 to ground level and remove excess basal shoots (preferably with a root). During the season, bush 1 gives a new shoot from the root, which by the next spring reaches 1-1.5 m in height under our conditions. The following year, in early spring, I shorten this shoot on bush 1 by 1/3 of the height. During the season, new side shoots will appear on bush 1, which will grow somewhere else by 1 m. In May next year, bush 1 will bloom gorgeously, and after flowering it will again undergo strong anti-aging pruning. This cycle is repeated for clusters 1 and 2 in turn in different years. Thus, every year I have a lush lilac bloom in my garden, but the bushes do not grow old and do not grow unnecessarily.

    After pruning lilacs

    After pruning, fertilize lilacs with nitrate and phosphorus fertilizers, and then thoroughly mulch. Lilac prefers neutral soil acidity, keep this in mind when mulching (see the link above for the features of different types of mulch).

    See also: Pruning fruit trees in spring, Pruning berry bushes

    In the UK and some other countries, it is not customary to pick a lilac, give it as a gift and put it in a vase at home. Intrigued, I found an interesting explanation for this custom on the Internet. It turns out that before the widespread use of modern embalming agents, lilacs during the flowering period were widely used in houses where the body of the deceased was awaiting burial, to mask the smell of decomposition. So, on the basis of unpleasant associations, a sign arose that the lilac at home brings misfortune and death. If you are visiting someone in a hospital in an unfamiliar country, choosing flowers, it is still best to stay away from lilacs so as not to inadvertently upset the patient or his relatives.

    * Photo schemes adapted from the magazine
    Fine Gardening

    Tags: trees & shrubs, pruning, lilac, flowers in a vase

    About Author

    Lilac pruning. Basic Rules and Tips

    Photo Flickr.com

    Tips, Care Views: 60 710 0

    Lilac belongs to shrubs for which correct and timely pruning is extremely important. She cannot be neglected.

    This article is a continuation of material "Rules for planting and caring for lilacs" .

    Sanitary and shaping pruning

    Sanitary pruning is best done in early spring (March - early April) and in summer immediately after flowering. However, if it was not possible to hold it in the spring, then one summer one will be enough.

    In the spring, remove all broken, damaged, frost-bitten branches (may form even in winter-hardy varieties if there were strong temperature changes) during the winter. It is also necessary to cut off the shoots that have grown under wet snow in early spring.

    Last year's growth is also removed if it is not necessary for propagation by layering: a large number of growth takes moisture and nutrition from the main plant, and also increases the size of the bush and worsens its appearance.

    In spring we do not recommend trimming lilacs in height and performing formative pruning: there is a risk of removing flower buds that are located on the top of the shoots.

    Formation pruning, as a rule, is combined with summer sanitary and carried out after flowering. The measure includes:

    Do not forget about the newly appeared growth, which also needs to be cut out.

    [stextbox id="info" caption="Advice" ccolor="000000" bgcolor="F4B0FF" cbgcolor="F4B0FF" bgcolorto="F4B0FF" cbgcolorto="F4B0FF"]After sawing off large branches, cover the cut with garden pitch. So you prevent the defeat of plants by infectious diseases.[/stextbox]

    Rejuvenating pruning

    This type of pruning is relevant for aging native-rooted lilac bushes, both varietal and specific. If there are already few shoots on the old branch, then cut it down to the ground. Within 2-3 years, replacement shoots will form from the young shoots.

    We do not recommend replacing all the old skeletal branches at once. It is better to do this gradually, 1-2 branches per year. Thanks to this, the plant will rejuvenate without losing its decorative effect.

    On grafted lilacs, rejuvenating pruning is carried out up to the trunk above the grafting site. An insulating material, such as garden pitch, is applied to the cut site.

    Pruning to regulate flowering

    Lilacs have a peculiarity - if one year it bloomed too abundantly, then the next year the flowering will be very weak.

    For this reason, regular pruning is necessary to ensure that the shrub blooms evenly throughout the year. It is carried out in early spring, before the start of the growing season. At the same time, part of the shoots with an excess number of flower buds is removed.

    Common lilac ‘Beauty of Moscow’

    Pruning of faded inflorescences

    This type of pruning is needed for laying next year’s flower buds on lilacs.

    If faded panicles are not removed in a timely manner, then the nutrients of the plant will be used for fruit ripening, and the number of new flower buds will decrease significantly.

    Never break or pluck out faded panicles. They only need to be trimmed, leaving small stumps.

    Cutting for bouquets

    Cutting flowering branches also activates the emergence of new flower buds. However, they should not be abused - we advise you to leave about half of the inflorescences on the bush.

    By cutting everything, you give the plant a signal to form a large number of new shoots, which will begin to grow everywhere, break the shape of the crown, and also deplete the plant.

    Do not break flowering branches: lacerations can lead to plant disease.

    Learn more