Pruning Lilac Bushes: When To Trim Lilac Bushes

Who doesn’t enjoy the intense fragrance and beauty of lilacs? These old-fashioned favorites are wonderful additions to nearly any landscape. However, periodic pruning is vital in order to keep lilacs healthy and looking their best. Although there are smaller varieties, about ten to fifteen feet (3-4.5 m.), many lilacs can reach heights of about thirty feet (9 m.) tall without regular pruning. Pruning lilac trees on a regular basis keeps them from becoming too tall and unmanageable.

How to Prune Lilac Bushes

When pruning lilacs, cutting back the tops of overgrown stems is oftentimes not enough. It is generally better to cut the entire stem. Trimming lilacs is best accomplished using clippers. Remove spent blooms all the way to the stems to prevent seeding and encourage more blooms later on. Cut back about a third of the branches. Cut away shoots growing near the ground that may be sprouting from the main trunk. In order to improve air circulation or to allow more light to filter through, trimming lilacs within the inner branches may be necessary.

If lilac bushes are already too large or becoming unsightly, however, pruning the entire bush or tree to about six or eight inches off the ground may be necessary. Keep in mind that you may have to wait for flowers, as it takes about three years for them to develop once entire shrub has been cut.

When to Trim Lilac Bushes

Knowing when to trim lilac bushes is important. Most lilacs don’t require pruning until they reach about six to eight feet (2-2.5 m.) tall. The best time for pruning lilac bushes is right after their flowering has ceased. This allows new shoots plenty of time to develop the next season of blooms. Pruning lilacs too late can kill young developing buds.

If you are pruning lilac trees or shrubs entirely to within inches of the ground, it is best to do so in early spring. New shoots will develop during the regular growing season as long as there are a few healthy shoots left. Once the growing season has ended, remove any unsightly shoots.

Pruning lilac bushes is important for their health and flower production. Lilacs are generally pretty hardy and if proper pruning is performed, they will come back stronger than ever.

Pruning Large, Overgrown Lilacs

The common purple lilac is a tough, reliable shrub that may reach a height of 15 to 20 feet. Unfortunately, as lilacs mature, the shaded lower portions of the shrubs usually lose their leaves. As a result, large, overgrown specimens are often leggy and unattractive. Old, neglected lilacs can be renewed or rejuvenated by pruning. Home gardeners can choose between two different pruning methods.

One way to renew a large, overgrown lilac is to cut the entire plant back to within 6 to 8 inches of the ground in late winter (March or early April). This severe pruning will induce a large number of shoots to develop during the growing season. In late winter of the following year, select and retain several strong, healthy shoots to form the shrub framework and remove all the others at ground level. Head (cut) back the retained shoots to just above a bud to encourage branching.

A second way to prune old lilacs is to cut back the overgrown shrubs over a three-year period. Begin the procedure by removing one-third of the large, old stems at ground level in late winter. The following year (again in late winter), prune out one-half of the remaining old stems. Also, thin out some of the new growth. Retain several well-spaced, vigorous stems and remove all the others. Finally, remove all of the remaining old wood in late winter of the third year. Additional thinning of the new shoots should also be done. Since lilac wood needs to be 3 or more years of age before it blooms, this pruning method should allow you to enjoy flowers every spring.

When properly pruned, an old, overgrown lilac can be transformed into a vigorous attractive shrub within a few years. Once rejuvenated, pruning should be a regular part of the maintenance program for lilacs. The shrub can be kept healthy and vigorous by removing a few of the oldest branches every 3 to 5 years.-

This article originally appeared in the February 10, 1993 issue, p. 8.

When Should I Prune Denver Lilacs?

The best time to prune Denver lilacs is just after the spring flowers have faded.

This is because lilacs set the next year’s flower buds immediately after the flowers have died. Late lilac trimming (or early, depending on how you look at it) will kill off these buds, thus the plant won’t produce flowers the next season.

Lilacs are hardy plants that can grow up to 20 feet high and have large, uniquely fragrant spring flowers, making the lilac bush a favorite among homeowners and plant care enthusiasts.

Lilacs are tenacious plants that will create many suckers that can quickly take over a yard, killing other plants as they go. This is why your lilac needs yearly pruning! Pruning a lilac isn’t difficult, but it’s vital to follow certain lilac pruning guidelines, or your plant will suffer – and you won’t be able to enjoy the springtime flowers the plant is known for.

Different varieties of lilac listed here.

In the picture above, pruning the lower half late in the year killed the following year’s flower buds, while pruning the upper half at the proper time allowed the plant to flower.

Another pruning rule is to never cut more than one third of a shrub’s stem, and always leave a little green on top. This will allow new stems to develop and old stems to peak and bloom.

Be wary of the company you choose for bush trimming services.

Most companies simply run a trimmer along the side of the bush without any knowledge of the bush in question. By doing this they could be doing more harm than good killing off the next seasons flowers, damaging the plant, and leaving an unhealthy-looking, ugly plant in your yard.

In contrast, having a quality company such as Arborscape do the work assures that the flowers will bloom as desired during the following season, the bush will be trimmed down to a healthy size, all deadwood will be cut out, and you’ll be left with a beautiful and healthy plant. Check out ArborScape’s page on shrub trimming.

More articles from our Spring blog: Go>>

How to Prune Lilac Bushes Video

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Felix from Gurney’s guides how to prune an old fashioned lilac, offering information on the bush’s growing and flowering behavior throughout the year.

Transcript

Good morning everyone, Felix here at Gurney’s and today I’m talking to you about lilacs and pruning your lilacs after flowering in spring and I’m standing by this nice, old specimen, it’s about fifteen years old here and it has some nice growth on it and some older canes and lots of options for teaching some pruning techniques, how you might want to manage your lilac plant. So we’re going to cover some detail there in this video. Alright everyone, so the first item I’d like to point out is the flowering habit of the lilac and this is of course the old fashioned lilac and they flower on last season’s growth. If you look closely here, this, here is actually where last spring, there was this shoot initiation just like this green one that’s breaking this spring. So last spring, the year prior, this was the shoot growth and you can see, the flowers, which are all finished now were up at the top tip and the second bud below typically on that last season’s shoot. So that’s where you get your flowering on your old fashioned lilac, is on the last season’s growth, the prior season’s growth. At this green shoot here is going to be where next season’s flowers are produced. So when you prune, you just need to keep that in mind and it’ll help you a lot in deciding, okay, how do I want to prune it and where do I want all my flowers. So that’s a key point about the old fashioned lilac, where do they flower – it’s on the tip, or just below the tip of the last season’s growth. Alright everyone, so here we are with our lilac and I want to point out the branches that I’m going to take out here. This is a specimen that I want to keep large because I have a space that I want to fill out along a fence line or I have a larger landscape and I want to keep the size large and all I’m doing is rejuvenating and getting new shoots to come up. And we have a branch here that I’m taking out that has a little bit of winter damage, the bark color doesn’t look quite as healthy, you can compare these two, and so that’s going to come out and then I’m going to take out some of these lagging branches here just to allow more light down to the base here which will stimulate new branch growth which are going to be future of this lilac. Alright, so for those of you that would like to have all your lilac flowers at about nose level, you can take an older specimen like this and right now, which is after flowering which we’ve pointed out, you want to go through here and actually just head this back, so can go through here and take out limbs right in here, you know, so your new shoot production is going to be right about here next spring and that’s where your flowers will be. So you just, can go through here and head back, like that, all along here and for some of these interior, you have a number of shoots that didn’t get enough sun last year, you can take those all the way back, clean that up because this tissue is no good and you’ll get initiations here, coming off this branch, all during the growing season, and those will flower next spring and that’ll give you your flowers where you want them and you can start doing that every year, you can take it back a little bit, keeping in mind the flowering tendency of the lilac – it’s on last season’s growth and that’ll allow you to manicure your lilac exactly how you want it, and have a lot of fun, folks.

Havet

We just moved into a new home, and I am trying to get the yard ready for winter. The front yard has black plastic down and bark all over, even under the lilac bushes. The lilac bushes are overgrown, and it is hard to get under them to get the plastic and the bark out. I was wondering if it is okay to prune them in the fall and, if so, how much is too much to prune back? This is the first time that I have had a yard, so I don’t know a whole lot.

Sandra Lake

Dear Sandra,
The best time — and only correct time, really — to prune lilacs is just after blooming. All shrubs fall into one of two categories; some, like many of the hydrangeas, bloom exclusively on new wood and can be pruned to the ground each fall if required. Others, such as lilacs, bloom only on old wood from the previous season. Thus, if you prune at any time other than immediately after flowering, you will cut off next year’s blooms. For lilacs, the recommended method is generally to remove one third of the old wood each year immediately after flowering and shape the shrub over a number of seasons. Of course, you can prune in the fall if absolutely required. Keep in mind, though, that you are cutting off all of next spring’s luscious blossoms in the process.

Azaleas: Keeping Them Healthy

Posted in Gardening Tips on May 26 2011, by Sonia Uyterhoeven

Sonia Uyterhoeven is Gardener for Public Education.

Rhododendron ‘P.J.M.’

Pruning

The best pruning jobs begin with a goal, a determination of what needs to be accomplished–reducing size, controlling shape, rejuvenating growth. As with all pruning jobs, removing the dead and diseased wood is the first call of order. Then take a step back and look at the framework before moving ahead with your mission.

See also: Native Azaleas

The best time to prune azaleas and rhododendrons is immediately after bloom into mid-July. If you wait too long, buds will already have formed for the following year. In general, azaleas and rhododendrons need minimal pruning.

Reducing Size

To reduce the height of an azalea while allowing it to retain its natural appearance, follow the branch targeted for removal down to a lower lateral branch, and make a cut just above the point of intersection. The cut should be slightly above where the two branches intersect so as not to cut into the tissue of the branch that will remain.

Another way of reducing the size of an azalea is to cut it back to just above a whorls of leaves. Also look for circular scars around the stem, where leaves once were. Cutting just above these areas should create good bud break. In either case, make the cut just above new buds, whether they are visible or latent.

Controlling Shape

Evergreen azaleas can be sheared back to form nice mounds if desired. If you are pruning the azalea into a mound, remember to occasionally open up the plant and let some light penetrate into the dense mass of foliage so that it doesn’t get too congested.

See also: Azalea Planting Tips

If you’d like to make a young azalea or rhododendron more compact and well-branched, the easiest thing to do is to pinch off the vegetative buds in spring. First take a look at the plant to familiarize yourself with the bud system. The fat swollen buds are flower buds. These form in the previous season and overwinter, and you’ll want to leave these alone. They are generally twice the size of the vegetative buds, which are the narrower, pencil-like, smaller buds.

The number of vegetative buds at the tip of a stem determine the number of new stems that will be produced. Sometimes you will find 2-4 vegetative buds, but more often, there will be just one. If you snap off this single vegetative bud (it will be about a half-inch long) with your thumb and index finger early in the season, immediately after flowering, you will induce the plant to produce more buds. Generally, it produces 2-4 buds at the same location, which will turn into 2-4 new shoots. In this way you can influence the branching structure of the plant.

Rejuvenating Growth

Some azaleas and rhododendrons get leggy over time. If the plant is misshapen or too large, you can prune it drastically. Such a rejuvenation pruning should be done early in the spring, mid-March to early April, in the New York area (usually 2-3 weeks before new growth starts). Cut the plant back hard to about 8-10 inches from the ground. You can cut the entire plant back or leave one or two smaller stems as a source of energy (these are cut back later once growth resumes). Remember to water the rejuvenated plant well during its first season. New suckers may need to be thinned mid-season.

Some rhododendrons, particularly the Dexter hybrids such as ‘Scintillation’, do not rejuvenate well. Many other rhododendrons and azaleas do. When rejuvenating an azalea or rhododendron, fertilize the year before to prepare the plant and then fertilize again in spring (end of April) after the hard pruning to stimulate growth.

See also: Azaleas A to Z: Know Them to Grow Them

For smaller azaleas, use bypass pruners to make the cuts. For larger jobs, you may need a folding saw or a pair of loppers. Work with sharp, clean tools. Tools can be sanitized with isopropyl alcohol.

It would be tedious and time consuming to deadhead azaleas and small flowering rhododendrons. But since seed production does take energy away from the plant, large flowering rhododendrons can benefit from deadheading.

Hold on to the stem and grab hold of the spent flower head. Snap it off being careful not to damage the new buds forming on the sides of the stem. Your hands will get sticky from this task; you can clean them with Tecnu® or some oil-based hand cleaner.

Rhododendron canescens ‘Varnadoe’s Phlox Pink’

Pests and Problems

In general, azaleas and rhododendrons are fairly problem free. Below are the most common problems encountered.

Lace Bugs

Lace bugs are rarely a problem for azaleas grown in the shade but can be a problem for those grown in full sun. The underside of the leaves will have stippling or small yellow spots, which are created when the small, mottled-wing insect pierces the leaves and sucks out fluid.

See also: Top Tips for Designing with Azaleas in the Home Garden

There are several ways to combat these pests: Spray the underside of the leaves with water in mid to late May to dislodge the nymphs; release natural predators such as green lacewings; or spray the foliage with insecticidal soap or horticultural oil in mid to late May and again in mid to late July, making sure to cover the underside of the leaves. Spraying works best with 2-3 applications separated by 5-7 days. Always read the instructions when applying pesticides.

Black Vine Weevils

Black vine weevils are small beetles with a long snout that eat c-shaped notches into the leaves of rhododendrons and azaleas. These beetles are nocturnal feeders that hatch in mid-June. Go out at night with a flashlight and either pick them off by hand or place a white sheet under the plant and shake them off.

The grubs cause the real damage, hatching at the base of the plant and eating away at the root system. They can be treated with nematodes in April-May and again in August. Nematodes that specifically treat black vine weevil grubs are available. Do not apply in direct sunlight, keep the soil moist, and always read application instructions.

Powdery Mildew

Powdery mildew affects many decidious azaleas. Good air circulation and increased levels of light help avoid this problem. Options for control include products derived from neem oil, potassium bicarbonate (GreenCure®), Bacillus subtilis (Plant Guardian™), and selective pruning.

Wind Burn

Wind burn on foliage is a common problem and happens when azaleas and rhododendrons are exposed to sun and drying winds in winter. Mulch and water the plants well in fall. A burlap windbreak also helps as can anti-desiccants: apply once in late November-December and again in late January. Prune damaged foliage in spring.

Tips for Beginners: How To Prune Evergreen Azaleas

Tom Hughes
Oak Ridge, Tennessee

Many evergreen azaleas never experience the pruning shears, since, for the most part, these plants are naturally well behaved. If they are carefully selected, carefully sited, carefully planted, and properly tended, there is usually little need to prune them in the informal garden. Nevertheless, there are some situations in which pruning can be useful, enough to justify a look at the subject.

Evergreen azaleas have a big advantage over some other garden shrubs when it comes to pruning – lop off the end of most any branch or twig that is not heavily shaded and a healthy plant will soon activate new buds (called adventitious buds) below the cut end. For good results, however, it’s best to prune with a plan that takes other factors into account.

Why prune? First of all, to remove dead wood. Branches may be killed by cold over the winter or die in mid-summer after girdling by a hard frost in the spring. They may die back as a result of fungus attack, shading, borers, lack of water or improper fertilizing. Cut out the dead wood back to sound wood, i.e., where a nick with the fingernail reveals a layer of green cambium under the outer bark. If the cut end is more than a quarter of an inch across, I zap it with some aerosol wound dressing to discourage new invasion by fungus or borers. (Incidentally, when fungus is involved, the pruning shears should be sterilized after each cut by dipping in a fairly strong solution of sodium hypochlorite in water.

One of the most common reasons for pruning evergreen azaleas is to scale back an exuberant bush that is beginning to cover a window or crowd a walkway. Pruning would be unnecessary if a smaller-growing variety had been selected initially and positioned properly when planted. It is possible, however, to keep ambitious plants in bounds by regular judicious pruning. The secret here is to reach below the surface – follow projecting branches back a suitable distance into the bush to functions with other branches and cut them off flush. In this case don’t leave stubs, which would probably die from lack of light and could invite fungus invasion. The overall effect is to reduce the size of the plant without destroying its symmetry. The surface of the plant will not be as dense at the outset but should fill in quickly.

Another common reason for pruning is to improve the appearance of tall leggy plants with ugly bare shanks and knobby knees. In these cases major surgery is often needed. Judgment is called for, but in serious cases I usually cut the offending stalks back to within a foot or so of the ground in spring (and spray the cut ends with wound dressing), leaving some low branches intact. Cutting so early will destroy the current year’s flowers, of course, but new shoots will start earlier and recovery will be quicker. Strong-growing new shoots should be pinched once or twice up to early August to encourage branching.

Also, some varieties send up suckers from the base of established plants. These usually are shaded out eventually, so it’s best to prune them away while they are still small. When the plant is young, however, I like to make sure that it will develop a bushy habit rather than a single trunk like a tree. This means that at least three main branches should be left growing from the base of the plant. That way, if a major calamity such as a borer strikes, all is not lost.

Another reason for pruning is to increase the density of twigs and flower buds on plants of naturally rather open growth. This is accomplished by pinching or shearing the new growth during the growing season to induce branching. Timing is rather critical if optimum results are to be achieved. Not all shoots on a plant are ready for pinching at the same time, and not all varieties ripen at the same time. If the new shoots are pinched too early, while they are still soft, the likely result will be a single new branchlet replacing the nipped growing point, and nothing is accomplished. If pinching is done at the right time, however, several buds will break below the point pruned. I usually wait till late June or early July, depending on variety, when the new shoots tend to snap when bent double. This is also the time to take cuttings for propagation, doubling one’s reward for waiting.

Selective pinching of the terminal buds to increase branching can continue up until about the first week of August (later in the South). Pinching or shearing must stop while there is still enough of the growing season left to allow the plants to set flower buds for the next spring’s show. Late pruning will take away the flower buds for the following year.

In formal garden, like some Japanese gardens, evergreen azaleas are often sheared to smooth rounded shapes. This is fine and gives results that are pleasing to many people, but, as we indicated earlier, shearing must stop in time for the plants to set flower buds.

In summary, the first rule of pruning is to select the right varieties in the first place and plant them where they’ll do what you want without a lot of pruning. There are hundreds of varieties to choose from, dwarf, medium and tall, in many colors, blooming early and late. The second rule is to stop pruning while there is still time for the plant to set flower buds for the next year: around the first of August in the Mid-Atlantic region, and late August in the South. Third, don’t leave stubs when pruning larger branches; cut them off flush with another branch.

Steps To Prune An Azalea Bush: How Do You Prune An Azalea

Azaleas are a popular yard shrub due to their ability to bloom in a wide variety of conditions and their vibrant colors. But many homeowners wonder how do you prune an azalea to keep it a manageable size and shape. Pruning azaleas is easy and can be done with a few simple rules in mind. Let’s look at how to trim azalea bushes.

When to Trim Azaleas

The best time when to trim azaleas is after the blossoms have faded but before the new blossom buds have started. The next year’s blossoms typically start forming at the beginning of July, so you must prune an azalea bush before then.

If you prune azaleas after the beginning of July, you may not get any flowers on the bush next year.

Tips for Pruning Azaleas

So, how do you prune an azalea? First, azaleas should be pruned in a natural fashion as they are not well suited for formal styles of pruning. Trying to prune an azalea bush so that is has straight edges and is box shaped (as would be seen if cut with hedge clippers) will result in spotty flowering and splotchy growth of branches. Instead, when pruning azaleas, use pruning shears to cut individual branches at the proper spot.

Next, think about why you are trimming your azaleas. Is it to create a better shape plant or to maintain size or to rejuvenate the azalea plant?

If you are shaping or maintain the size of your azalea, then mentally picture how you would like the azalea bush to look. Keep in mind that a natural and not formal look is best. Pick out the branches on the plant that are outside of your mental shape for the plant and cut each one of those back. Try not to cut any one branch back by more than a third.

When pruning azaleas, you do not need to worry about cutting back to a connecting branch. Azaleas will grow new branches from right below wherever you cut.

If you are pruning an azalea in order to rejuvenate the plant because it is spindly or sparse, locate three to five of the largest branches on the azalea bush. Cut these branches back by a third to a half. Trim all of the other branches on the plant as though you were shaping the plant.

Now that you know when to trim azaleas and how to trim azalea bushes, you can keep your azalea bushes healthy and looking fabulous. Pruning azaleas is a great way to maintain these wonderful plants’ beauty.

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