Many flowering shrubs (including lilac bushes) require consistent pruning for the best blossoms and to maintain the plant’s health. However, it can be difficult to tell how to do this properly and when to do it. Timing is incredibly important for pruning, making it crucial to know when to prune lilac bushes, so you don’t end up damaging future growth.
Any time after June is too late to prune lilacs. Lilacs should be pruned between April and June after the plant has finished flowering. Pruning too late will damage next year’s buds and cause you to have a flowerless season.
If you want more information on when to prune lilacs and how to do so, I’ll explain both of these in the rest of this article. I’ll also discuss other reasons (apart from incorrect pruning) you may be getting disappointing blooms. If you’re ready to become a lilac pruning professional, keep reading!
Why Late Pruning Is Bad for Lilacs
Lilac plants flower on the previous year’s growth, so pruning after June will damage the next season’s buds. The best time for pruning is when the lilac bush has finished flowering.
New lilac buds start to form at the end of the growing season and continue maturing through the winter. So if you prune too late, you’ll cut away some of these new buds and cause a disappointing blooming season next spring.
You should prune mature lilac plants directly after the flowers begin to fade for the best results. Additionally, if you prune early enough, the young buds will have more time and energy to grow because the plant is no longer working to keep the previous year’s blossoms alive. This is exactly why timing is essential for successful pruning.
Even if you don’t have time to completely prune your plant right after blooming, you should at least deadhead the plant. This is the process of removing dead flower heads to promote continual blooms and enhance flowering performance.
You may be worried that lilacs won’t grow back after being cut, but cutting, trimming, and pruning lilacs is essential for future growth. For more information, read my article: If You Cut Lilacs Will They Grow Back?
How to Prune a Lilac Plant
Pruning involves trimming a plant to promote future growth. You cannot say you’ve properly cared for a lilac plant if you don’t prune it.
Pruning can keep pests and diseases at bay and help a plant keep its shape. It also allows sunlight to distribute evenly and promote new growth. To reap these benefits, you have to prune your lilac correctly.
Now, let’s begin the pruning process:
Time Your Pruning Well
Prune your lilacs at the end of the growing season. As I’ve mentioned, if you don’t time your pruning right, you could end up not seeing your lilacs flower in the next season.
Gather & Prepare Your Tools
Get the right tool, such as high-quality bypass pruning shears. For thicker stems, I suggest using a pruning saw instead of shears.
You should also make sure you disinfect your tools. That way, you can avoid spreading any harmful microorganisms that may have grown on the tools to your plants. I suggest using rubbing alcohol or disinfectant spray for this purpose.
Address Unhealthy Stems
Cut any unhealthy stems to the ground. If you don’t get rid of these stems, you’ll risk infecting the other healthier stems. Also, you’ll improve sunlight distribution and air circulation, making your plant healthier.
Shape the Bush
You can shape your lilac by trimming long, thick stems. Part of proper pruning is ensuring that the plant’s shape stays consistent. The best way to do so is to trim to the side and go beyond the flowering part.
Limit the Pruning!
Prune only less than one-third of the branches. Unless your lilacs are severely affected, you shouldn’t cut more than a third of their size. Otherwise, you won’t see any flowers next spring.
Reasons Your Lilacs Aren’t Blooming
Improper pruning and pruning at the wrong time are some of the main reasons why lilacs may not bloom, but there are other explanations as well.
If you haven’t pruned your lilac plant after June and you’re still getting disappointing blooms, here are some possible reasons why:
They Aren’t Getting Enough Light
Lilacs require a lot of sunshine, so if you aren’t getting as many blossoms as you’d like, make sure your lilac plant is in a place where it can get at least six hours of sunlight. If it isn’t, you should replant your lilacs in a sunnier place.
The Plant Is Old
Lilacs bloom best on young wood, so blooms will struggle to grow if you haven’t been pruning and rejuvenating your lilac plant for 5 years or more. To fix this issue, you’ll need to do a rejuvenation pruning, which is more intense and thorough than typical annual pruning.
You’re Overwatering
Lilacs don’t need a lot of water. The soil should be consistently moist, but it should never be oversaturated. Too much water fills the air pockets in the soil, which lessens the amount of oxygen in the soil and chokes the roots.
The plant Has Winter Damage
Lilacs are hardy and can usually survive the winter without damage. However, in particularly cold climates, they may experience some injury that impacts flowering.
For more about lilacs in the winter, read: Should Lilacs Be Covered Before the Frost?
Your USDA Zone Isn’t Compatible
Lilacs grow best in USDA zones 3-7, so if you’re trying to grow lilacs in a zone outside this range, you may struggle to see healthy and abundant blooms. In that case, consider growing a different flower species instead.
The Soil Is Too Acidic
Lilacs struggle to flower in soil with a pH lower than 6, so if this is the case in your garden, lilacs will grow poorly, and you won’t see the blossoming you want to see. You can test your soil’s acidity with a soil test kit.
Your Fertilizer Has Too Much Nitrogen
Nitrogen encourages the growth of green foliage at the expense of flowering, so if you’re using a high-nitrogen fertilizer, you may notice more leaves and greenery than bright and beautiful blossoms. Try to use fertilizers high in phosphorus instead.
They’re Young or Recently Transplanted
Lilacs invest their energy in establishing their root system during their first few years, so if you recently planted your lilacs, it may take a couple of seasons before you see the number of blossoms you’d like to see. This is the case with replanting as well.
Your Area Is in a Drought
Even if you water your lilacs regularly, a drought can influence the soil lilacs grow in and how many nutrients they have access to. You can try adding compost and manure to the soil to give the lilacs the nutrition they need.
Hopefully, you’ll be able to determine the reason your lilacs aren’t blooming and fix the issue so you can once again enjoy the scent and beauty of lilacs in your garden.
Conclusion
If you’re planning on pruning your lilac bush, the best time to do it is between April and June, right after your plant has finished flowering. This is because the buds for the next season grow on the previous year’s growth, so if you prune too late, you’ll damage these buds and cause a flowerless season. Anytime after June is too late to prune lilacs.
