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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 Lilacs Like a Master Gardener

Photo: istockphoto.com

When considering how to prune lilacs, keep in mind that those shrubs reportedly flower better on newer wood, so you can do them a favor by removing some of the oldest canes. But “newer” is a relative term. Blooms usually don’t appear on wood younger than 3 years old, while 5- to 8-year-old canes generally produce the most flowers.

Therefore, your lilac bush care routine needn’t include pruning for a young shrub, except the deadheading of faded flowers and removal of dead or broken branches. However, once the lilac reaches 6 feet or so in height, it might appreciate rejuvenation pruning.

RELATED: How To: Plant a Bush or Shrub

When to Prune Lilac Bushes for Regular Maintenance

If you are debating on when to prune lilacs, the simple answer is that they should be pruned within 2 weeks after they finish blooming in spring. Cutting at any other time of year would be a mistake, since it’s during summer that lilac bushes begin making buds, which persist over winter for the next spring’s bloom.

However, should you prefer to prune when the plant is free of foliage, you can do so in late winter, even though you’ll be removing potential flowers that way. No matter which trimming option you choose, follow the steps below to learn how to prune a lilac bush.

Tools & Materials

BEFORE YOU BEGIN

Photo: istockphoto.com

It helps to know that these steps include routine maintenance pruning (which is minimal for lilacs) and rejuvenation pruning. When applied to pruning lilac bushes, rejuvenation pruning can suggest a drastic cutting back of those shrubs in late winter—to within about 6 inches from the ground—to promote all new growth. However, such extreme measures will eliminate all blooms for at least 1 or 2 years, since lilac buds begin forming soon after they completed their last spring’s bloom.

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When trimming lilac bushes for rejuvenation, therefore, most gardeners prefer to remove a third of the oldest canes annually for 3 years. That way, youthful vigor can be restored gradually without eliminating blooms.

Before pruning lilacs, soak the blades of your tools in a sterilizing solution—such as 70 percent rubbing alcohol or Lysol disinfectant—for 5 minutes to prevent the spread of disease. Then, rinse the blades in water and allow them to dry before use.

STEP 1: Deadhead your lilac bushes by removing faded flowers.

Photo: istockphoto.com

Begin pruning lilac bushes by removing all of the shriveled blooms as they fade. To do so, find the first pair of leaves beneath a faded flower cluster and snip just above those leaves. You should be able to use bypass pruning shears for this, unless the stems are larger than ¼ inch in diameter. In that case, try bypass loppers instead.

STEP 2: Remove dead, broken, larvae-infested, or rubbing canes at the base.

For the next phase of your lilac care routine, remove any canes that appear damaged or infested with pests such as the lilac borer. (Small holes at the bases of shoots, accompanied by sawdust, often indicate borers.) Where two canes are rubbing together, remove the weakest one to prevent it from damaging the stronger one.

STEP 3: To rejuvenate the bush, prune 1/3 of its old canes.

Photo: istockphoto.com

If your bush has aged enough to require rejuvenation pruning, cut out a third of the oldest (largest in diameter) canes, snipping them off at the base. You probably will need bypass loppers instead of bypass pruning shears for this. For canes larger than an inch in diameter, use a pruning saw instead.

STEP 4: Remove all suckers on grafted bushes and most suckers on others.

If your lilac is a grafted shrub, your lilac bush trimming procedure should include removing all of the suckers (new shoots that spring up at the base of the plant). Unless you’re growing a living fence, remove most of the suckers for a bush growing on its own roots, leaving only enough suckers to replace the older canes that you pruned.

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RELATED: 12 Fall Landscaping Mistakes to Know and Avoid

STEP 5: Remove another 1/3 of the oldest canes annually for 3 years.

Photo: istockphoto. com

After your lilac is a few years old or about 6 feet tall, remove another third of the old canes during the next spring, and repeat the process once more the following spring. Once all of the oldest growth has been cut out, you can allow the shrub to grow unchecked for about 3 years, after which point you should repeat the rejuvenation process.

STEP 6: Propagate new bushes with your lilac cuttings (optional).

If you are looking for information on how to propagate lilacs, keep in mind that the cuttings should be at just the right stage to root properly. Those that snap promptly when you bend them are the best fit for propagation. If the cuttings are too young and tender or too old and tough to snap, they probably won’t work. Snip 3- to 5-inch cuttings with at least two leaf nodes each and follow these directions for rooting softwood cuttings.

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Lilac pruning. Basic Rules and Tips

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Tips, Care Views: 60 616 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 trim

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, you need to remove all broken, damaged, frostbite (may form even in winter-hardy varieties, if there were strong temperature changes) branches 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. nine0003

In spring we do not recommend trimming lilacs in height and doing formative pruning: there is a risk of removing flower buds 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] nine0003

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 even annual flowering of the bush. 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. nine0003

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. nine0003

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. nine0008

Use a sharp garden tool to cut into bouquets. Pruning should be sufficiently long shoots up to two-year-old wood, while leaving no stumps.

It must be understood that when pruning lilacs, we are primarily pursuing the goal of obtaining abundant and strong flowering. Getting enough light, moisture and air, in the crown of a properly formed lilac, each skeletal branch has its own segment for development. Ultimately, pruning forms such a crown through which, as gardeners say, in winter a sparrow can fly without hitting branches with its wings. nine0003

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:

  • removal of sick, withered branches
  • shortening or removing broken and frozen shoots
  • branches resting against construction objects - a house, a fence (to prevent their friction and injury, since fungal infections penetrate the plant through injuries)
  • if the plant is grown in bush form, then in the removal of propped shoots
  • if lilac is grown in standard form, then in the removal of basal shoots
  • thinning the crown, removing overlapping shoots and shoots growing inside the crown, thickening it

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

Early spring pruning to control lilac blossoms

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 the 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:

  • pruning of faded flowers
  • pruning the tops of the shoots to form an even crown shape (it happens that some shoots grow especially strongly, protruding from the total mass of branches)
  • pruning broken shoots
  • removal of severely depressed, poorly developing branches
  • removal of shoots damaged by diseases and pests
  • crown thinning
  • removal of branches that do not give normal growth (with an abundance of small branches) - in order to rejuvenate
  • pruning or removing branches with dead tops
  • removal of shoots rubbing against each other
  • thinning or removal of root growth

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 self-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.

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