Most flowering shrubs require that you prune them regularly to keep them vibrant, and the Lilac is no exception.
Normally, the Lilac (Syringa vulgaris) tree will flower with little or no effort from you. However, if left on its own to grow and spread, the Lilac tree may eventually only flower on the tops of the uppermost branches.
The best way to revive and extend the lifespan of a large, overgrown lilac tree is to prune the plant, and leave it within 6 – 10 inches on the ground — especially in March or April (late winter). When you cut back lilac tree like this, you’ll cause the tree to product a number of shoots to develop during the growing season.
Therefore, you should always prune your lilac tree(s)/bushes annually to maintain their form and create a balance of new flowering shoots and older stems.
More so, you might need to carry out a more extensive “rejuvenation” pruning on your Lilac trees with very thick stems and minimal flowering to revive them.
This post presents a complete guide on how to prune and rejuvenate a Lilac tree.
When to Prune a Lilac Tree
Most newer varieties of Lilac trees grow very quickly and may need pruning in their second or third year.
General, when a stem grows more than 2in. in diameter, it should be pruned. If you’re diligent and consistent with pruning your lilac annually, the Lilac tree should grow to about 8ft. tall with flowers all through the branches.
The best time to prune mature lilac plants is just after the flowers have faded in the spring. Note that Lilac trees bring out next season’s flower buds almost immediately, so late pruning means you’ll have to sacrifice the next year’s flowers.
Aside from the fact that early pruning helps the Lilac tree to grow flowers the following year, it also gives new shoots more time, more nutrients, and energy to develop – ensuring lots of flowers for the following season.
What You’ll Need to Prune a Lilac Tree
Here are the tools and materials you would need to prune a lilac tree:
- Bypass pruner
- Pruning saw (optional)
- Stepladder (optional)
How to Prune a Lilac Tree?
As stated earlier, there are two kinds of pruning, which are regular maintenance pruning and rejuvenating pruning. This section covers how to carry out both pruning methods:
1). Regular Maintenance Pruning
The general rule for pruning shrub is to cut at most one-third of the stems each year and the stem to cut must have grown more than 2in. in diameter. This will help the Lilac tree to remain vital always, enabling new stems to develop while old stems set flowers.
Mind you, the essence of pruning your Lilac tree is to have a Lilac tree that has about eight to 12 stems of various ages with all of the stems between 1in. to 2in. in diameter. Here’s how to carry out regular maintenance pruning:
i). Prune Unsightly Features
Start maintenance pruning by cutting off dead or diseased stems, pencil-thin suckers, and twiggy growth. Cut back all of these to ground level. You can use loppers or pruning shears to achieve this feat.
ii). Prune Any Stem Thicker Than Two Inches in Diameter
This involves removing the entire old stems – stems thicker than 2in. in diameter. This will prevent your Lilac tree from becoming too tall. When cutting off old stems, avoid cutting off just the top of these stems as this can leave the Lilac tree with an odd, unnatural shape.
You might need a pruning saw to cut down very large stems as thick Lilac stems can be very tough.
3). Prune Remaining New Stems
You need to do this if you want your lilac tree to fill in more and become shrubbier. This doesn’t mean you should cut off any new stems but cut off just the remaining new stems to an outward-facing bud.
This means you should prune just beyond buds that face away from the center of the plant. Doing this will cause more branching and create a denser shrub.
Without pruning, older lilac trees can have stems as thick as small trees and will bloom only on the topmost branches.
However, with rejuvenating pruning, you can revive an old lilac tree in about three years. There’re two major approaches you can take toward rejuvenating pruning:
i). The Third Rule
This is a less drastic approach to rejuvenating your Lilac tree and getting your overgrown lilac tree back into shape. Just as the depicts, this approach involves pruning a third of all the oldest stems/branches to the ground every year for three consecutive years.
You can start by taking out the thickest stems/branches first.
Though you may lose some flowers in the current year, it is worth it, and pruning an overgrown lilac tree is easiest early in the spring before the stems leaf out. After the third year of consistent pruning of your overgrown lilac tree, new shoots should make up most of the tree.
Your Lilac tree will begin to bloom all over, and you can begin to carry out regular maintenance pruning from that point onward.
ii). The Quicker Approach
If you feel the three years is so long for you or you can’t stand the awkward look of your old lilac tree for three years and you just want a quicker way out, then this approach is for you.
This approach takes a drastic measure of cutting back the entire Lilac tree to about 6in. to 8in. above the ground in the early spring. You would have to fertilize the Lilac tree with either compost or balanced chemical fertilizer to promote new growth.
Development of new shoots will occur all through the growing season. Allow new shoots to grow through the summer and you can cut out the spindly growth the following spring. Maintain the healthiest shoots while also considering the shape of the plant.
Encourage more branching and create a denser shrub by cutting back the remaining shoots to just above a bud. Then, continue with regular maintenance pruning after this.
Important Tips for Pruning Lilac Trees
Not all varieties of Lilac require maintenance pruning. For instance, dwarf lilacs like “Miss Kim” Manchurian lilac (Syringa pubescens ssp. patula “Miss Kim”) and “Palibin” Meyer lilac (Syringa meyeri “Palibin”) rarely require maintenance pruning.
However, you may still prune these lilac varieties when necessary for shape.
Your lilac tree can also benefit from deadheading. Deadheading is the act of removing dead or spent flowers from the lilac tree by hand.
Although this practice helps to stimulate continuing blooms in some plants, it doesn’t do much in Lilac trees. Deadheading only seems to make Lilac trees bloom better during the first few years of growth.
Normally, new lilac trees should begin flowering within two to five years.
While the lilac tree is young, deadheading the tree will help it to channel its energy into setting more buds.
However, once the lilac tree has mature, it won’t need deadheading to stimulate blooming anymore. You’ll likely have so many flowers on the Lilac tree that the task of deadheading would be too time-consuming.
Nevertheless, just as with any other flowering shrub, don’t expect your lilac to bloom magnificently every year. In some years, your lilac tree may bloom magnificently while in other years, it may not bloom so much. Blooming often depends on the weather.
A summer with extreme weather may yield fewer blooms while a pleasant summer with favorable weather may reward you with abundant flowers.
So you don’t have to panic if your lilac tree isn’t as vibrant this year. As long as your lilac tree is healthy and you observe the regular maintenance pruning and rejuvenating pruning, abundant flowers will follow.
Now you’ve learned how to rejuvenate a lilac tree from our complete guide.
Don’t forget that if you properly prune and rejuvenate an old, overgrown lilac, you can transform it into a vigorous and attractive shrub within a few years.