How to Trim a Lilac Bush

How to Trim a Lilac Bush

Lilacs are one of the most beloved shrubs for a variety of reasons, including the lovely lavender color of the flowers and the recognizable scent. When grown properly, a lilac bush can become tall, full, and survive for many years. However, one issue that lilacs often face is when their owners become too excited or enthusiastic when it comes to trimming and pruning lilacs. Instead of trimming constantly to eliminate little stems and dead flowers, it is actually better to keep trimming to a minimum. This article explains how. 

Pruning Lilacs: How to do it?

The ideal time to trim a lilac bush will vary based on whether you are trying to perform regular maintenance or are seeking to rejuvenate your lilacs in preparation for another year. Both processes require the same tools – gloves, a bypass pruner, and a lopper – and can take between one and two hours depending on the size of the bush and its proximity to other plants. As a general note, only trim the bush once a year, and try to do so after the flowers have just started to fade for the best results. 

Regular Maintenance

There are some basic rules for trimming lilacs:

  • When pruning, remember to wear gloves and use the appropriate equipment.
  • The most important one is to avoid cutting away more than ⅓ of the stems each year. When someone trims more than this amount, they start to eliminate important growth that will keep the lilac bush strong and full in the upcoming year. Instead, try to take as little as possible so the lilac can utilize the old growth to create new stems and blooms.
  • Start the process by eliminating dead or diseased stems, which can cause future issues. Then, try to trim away any stems that are thinner than a standard wooden pencil. Cut these all the way down to the ground level for the best results. If you’re worried about taking too much from the bush, then leave a couple behind.
  • Your next step is to cut away some of the stems that are thicker than 2 in. in diameter. These thicker growths can become tall and unkempt quickly, so it’s best to remove some of the old ones to keep the shrubbery in shape. This is where a bypass pruner or pruning saw comes in handy because lilac stems are notoriously thick and difficult to slice.
  • Finally, to foster more outward growth, trim back new stems so there is an outward-facing bud at the ends. This encourages the lilac to grow outwards rather than up, creating a thicker bush.


Lilacs are some of the hardiest shrubs capable of growing in the temperate zones, meaning they can shoot up to 15-20 ft. tall in several years. Unfortunately, tall lilac bushes suffer from leggy, unattractive lower halves. As the plant grows, the bottom branches slowly begin to lose their flowers and leaves, resulting in exposed stems topped with regular leaves and blooms. To counteract this problem, gardeners can trim the lilac bush with rejuvenation in mind instead of regular maintenance. 

Pruning Lilacs: How to do it?

Pruning Lilacs: When to Trim a Lilac Bush

A common problem with amateur and experienced gardeners alike is the tendency to go heavy-handed with maintenance. While a little care is required to keep plants healthy and strong, getting too happy with the pruning shears early in the life of flowers like the lilac results in stunted or dead plants.

You should resist the temptation to prune or trim your lilac bush until it is at least 6 ft. tall, which typically occurs during the second or third year of growth. At this point, there will be enough excess stems and blooms for optimal shaping. As a general rule, you should only trim stems that are at least 2 in. in diameter and are healthy enough to survive the change. If you are diligent and mindful about pruning, you can expect the lilac bush to reach 8 ft. in height around year four.

While most flowers shouldn’t be pruned until flowers are dead, the lilac is an exception. Lilacs begin to prepare for next year’s blooms as soon as this year’s flowers start to fade, so it essential to begin trimming just at the flowers start to lose their purple luster. Pruning or trimming too late will sacrifice next year’s flowers while starting early can actually maximize the benefits of your bush. 

Pruning Lilacs: Do Lilacs Need Deadheading?

Deadheading is when a gardener uses their hands to remove blooms that have started to wither and die on a plant. It is often done by individuals who want to keep their flowers healthy and encourage future growth. Although deadheading can be beneficial for some flowers, it doesn’t do much for the lilac except during the first year of growth.

During a lilac’s first year, deadheading can be used to encourage healthier, stronger blooms and to stimulate the plant so that it produces more than one flower in a certain location. When done correctly, deadheading can be a part of the pruning process for 2-3 years after planting. However, this means you need to target the blooms just as they are withering and dying and try not to break the stem when pulling them away. 

Once a lilac has started to bloom on its own, deadheading will have no purpose. Instead, stick to basic trimming and pruning and don’t force the flower to produce when it isn’t capable. The only exception to this rule is the dwarf lilac, which shows some minor benefits when deadheaded because of the small size of the shrubbery.


Lilac bushes are simple, beautiful, and easy to maintain. While the woody stems can grow rapidly and sometimes because thick and unwieldy, the solution is an annual trimming that focuses on fostering new growth and eliminating potential issues before they have a chance to develop further. If you have a lilac bush that needs pruning, don’t forget to start just after the lilac blooms fade for the best results.