All lilacs should generally be clipped right away in the spring after they have finished blooming. Lilacs set their flower buds for the following year immediately after the current year’s flowers have faded, therefore trimming later in the summer or fall will result in the removal of most or all of the blossoms for the following year. The larger common lilacs as well as the shorter or more “shrub like” cultivars are all subject to this timing guideline. While the “when” of lilac trimming is rather simple, the “how” is a little more difficult. For the time being, we’ll refer to lilac pruning as either maintenance pruning or rejuvenation pruning to keep things simple.
How should a lilac bush be trimmed?
Lilacs are a nostalgic flower for many individuals. On our property in Kansas, my mother planted a lot of lilac bushes. As I played, the aroma spread across the yard. In order for our children to share the same exquisite recollection of the aroma and flower, my husband and I made it a priority to plant a lilac in our garden when we first started our family.
I’ve tried, and have failed, through the years to bring this flower’s bounty into my house. Even though I had the flowers in a spotless vase filled with new water, they would begin to wilt an hour after I brought them inside. I have figured out how to make the blooms last as long as possible by trial and error:
As you trim blooms, have a pail half-full of fresh, chilled water nearby. Choose a chilly morning or evening to pick flowers. Lilacs bloom very sporadically after being harvested, so look for stems with at least 75 percent of their flowers open. Next, remove all of the leaves to prevent the plant from exerting extra energy to keep them moist. Put stems in the liquid. Allow the flowers to absorb water in the bucket for at least an hour by placing it in a cool, dark location.
Recut the stem ends next with powerful clippers, then make 1-2 inch vertical slices up the stem. Take hold of the sliced stem’s one side and twist it backward. Reintroduce the chopped stems to the water in the bucket right away. For an additional hour or two, let the stems soak up extra water in a cool, dark location. After that, the lilacs will survive three to four days and be ready for arranging.
What happens if a lilac shrub isn’t pruned?
It’s crucial to know when to prune lilac bushes. Most lilacs don’t need to be pruned until they are between 6 and 8 feet (2 and 2.5 meters) tall. Lilac plants should be pruned as soon as the flowering is finished. This gives new shoots plenty of time to grow before the upcoming blooming season. Lilacs can lose young, budding buds if they are pruned too late.
Early spring is the ideal time to prune lilac bushes or shrubs completely to a few inches above the ground. As long as there are still a few healthy shoots present, new shoots will continue to grow throughout the normal growing season. Remove any ugly shoots when the growing season is finished.
Lilac bushes’ health and bloom output depend on regular pruning. Lilacs are typically quite hardy, and with the right pruning, they will grow back bigger and better than before.
How much may a lilac shrub be pruned back?
Cutting no more than a third of the stems from a shrub should be the general guideline when pruning it. While a result, the plant will continue to thrive and grow new stems as the old ones bloom. Your aim is to grow a lilac bush with between eight and twelve stems, all between one and two inches in diameter, and of varying ages.
Prune Unsightly Features
Pruning should start with the removal of diseased, dead, and pencil-thin suckers and twiggy growth. Trim these all the way to the ground. These stems are typically handled by pruning shears or loppers.
Remove Any Stems Thicker Than 2 Inches in Diameter
By routinely removing entire old stems, you can keep your lilac from growing too tall. Removing only the tops of lengthy stems might cause the plant to take on an unusual, unnatural shape. A pruning saw could be essential for stems that are quite large. It can be difficult to handle thick lilac stalks.
Prune Remaining New Stems
Pruning the remaining new stems to an outward-facing bud will encourage your lilac to fill out more and develop a shrubby appearance. This entails trimming just past buds that point away from the plant’s core. A denser shrub will result from this technique’s increased branching.
Do lilacs require pruning?
An old, overgrown lilac was one of the few plants that endured my garden restoration. The fact that it obscured my neighbor’s garage and, more importantly, sported steel-blue double flowers, led me to rescue it. Although the blossoms on this shrub were both lovely and fragrant, it was difficult to appreciate them because there were so few of them. I decided to go with a rejuvenation pruning because I knew there was no reason to give up on this long-neglected plant because lilacs can handle severe pruning.
On stems that are no older than five or six years, the common French lilacs (Syringa vulgaris cvs.) yield the most and the largest flowers. The flowers get fewer, smaller, and farther away as the stems get older. A lilac, however, may reliably produce blossoms for decades with the right trimming. The method you choose will depend on how old your shrub is. Plants are maintained annually to keep them healthy. A more drastic trimming may be necessary for lilacs like mine that have seen better days.
Lilacs should be clipped annually to encourage healthy stem development and strong growth that improves flowering. Cutting sick, deformed, and unproductive stems to the ground constitutes annual pruning. I thin and cut back some stems as well to promote healthy, evenly spaced growth. To prevent them from growing too far away from the center of the plant, I also pruned a few of the new shoots that emerged from the roots. I left a few inches between each stem to prevent crowding. Since they produce the most, I maintain the pencil-thick shoots that extend all the way to the ends of the branches. Small, twitchy growth is unproductive and won’t blossom. This growth can indicate an excess of aged, unproductive stems or too much shadow. Remove stems as soon as possible after blossoming, or in late winter if you don’t mind losing a few blooms. Cut off stems and shoots at or just below the soil line.
Dwarf lilacs rarely need pruning
Both the “Palibin” Meyer lilac (Syringa meyeri “Palibin”) and the “Miss Kim” Manchurian lilac (Syringa pubescens ssp. patula “Miss Kim”) are twiggy-habiting, somewhat small lilacs. On these types, just deadheading is needed in terms of pruning. You can prune some of the older stems as the plants get older to make place for younger, more robust stems. In contrast to regular lilacs, these plants hardly ever spread out of control. They might never need to be entirely regenerated if you only undertake a tiny amount of trimming every few years.
After the blooms have faded, deadheading, another aspect of annual maintenance, should be carried out as soon as feasible. Just above the two new shoots that slant out from the stem that stopped with the old bloom, the base of the old flower cluster should be cut off. The new shoots will develop throughout the course of the summer, produce flower buds, and culminate in a cluster of flowers the following spring. While not as crucial as the annual thinning, eliminating the old blossoms enables the plant to focus more of its energy on developing robust branches and flower buds. In June, I deadhead and thin my plants as needed.
While performing this yearly maintenance, I occasionally come upon a young, robust shoot that may be getting too tall but is still a good, productive stem and is a candidate for tipping off. I cut the wasted flower’s entire top stem back to one or two side shoots at the desired height rather of just cutting it off at the base. The side shoots that are now near the top of the bush are encouraged to grow vigorously and develop flower buds for the following year by this cut, which also aids in shrinking the shrub.
My own old, overgrown lilacs need more severe pruning. I went outside in the early spring before growth got going to get a good look at the bush. I looked to see if the plant had been grafted before I began chopping. I immediately cut it down to the ground as it hadn’t (for a grafted plant, see the panel below). I recognized that this drastic trimming would result in the plant losing part of its aesthetic appeal for a few years because lilacs bloom on the growth from the previous season. However, I was also aware that the reward—more blossoms and a stronger plant—would be worthwhile.
It’s crucial to nourish the plant after rejuvenation pruning with compost, composted manure, or a balanced chemical fertilizer and to make sure the soil pH is close to neutral, which lilacs appreciate. In the upcoming years, these supplements and some high-quality mulch will help to encourage vigorous new growth and enhanced flowering.
Has your lilac been grafted?
If your lilac has been grafted, check it out before you start making cuts to the stems. Grafting is a method of plant multiplication in which the scion, or branch, of one species is joined to the rootstock, or stem, of another species. This is typically done to enhance a plant’s look or traits. A graft union, where the cultivar’s scion wood joins the rootstock several inches above ground level, should be obvious. An apparent change in the bark from the rootstock to the scion’s bark, as well as a little swelling at the graft union, are things to watch for. If your plant has been grafted, all of your cuttings must be made above the graft union, and you must prevent shoots from the rootstock from developing into new flowering stems. Flowers of the desired shape or color will not be produced by shoots that emerge from the rootstock.