Lilacs are beloved for their fragrant, beautiful blooms that light up gardens in the spring.
However, to ensure your lilacs come back strong after a harsh winter, it’s important to start preparing them in September.
With the right care—like proper pruning, mulching, and protecting against frost—you can help your lilacs weather the cold months and flourish next season.
I’ve learned through years of growing lilacs that taking a few simple steps now can make all the difference.
Follow these tips to keep your lilacs healthy and ready to bloom when spring rolls around.
Prune Lilacs Lightly After Flowering
One of the first steps in preparing your lilacs for winter is making sure they’re properly pruned, but September isn’t the time for heavy pruning.
Lilacs set their buds for next year’s blooms right after they finish flowering in late spring or early summer, so you should only do light maintenance trimming in the fall.
If you haven’t pruned your lilacs after they flowered, resist the urge to do major pruning now, as this could remove next year’s flower buds.
Instead, focus on removing any dead or damaged branches that could cause problems over the winter.
I always inspect my lilacs in September and snip away any branches that look unhealthy or are crossing over each other, which can lead to breakage in high winds.
In my own garden, I made the mistake of doing a heavy prune on my lilacs one fall, and the next spring I had very few blooms.
It was a hard lesson, but since then I’ve stuck to trimming only what’s necessary in September, and my lilacs have flourished year after year.
Mulch for Insulation and Root Protection
Mulching your lilacs is one of the best ways to protect them from the harsh winter temperatures.
Lilac roots benefit from a consistent soil temperature, and a thick layer of mulch can help regulate the ground’s warmth while also preventing moisture loss.
In September, after you’ve cleaned up the area around your lilacs, apply a 2-3 inch layer of organic mulch around the base of the plant.
Good choices include shredded bark, straw, or compost, which not only insulate but also break down over time to enrich the soil.
Make sure to keep the mulch a few inches away from the trunk to avoid trapping moisture against the bark, which could lead to rot.
Mulching has been a game-changer for my lilacs, especially in areas where winters can be unpredictable.
The extra protection keeps the roots safe during sudden cold snaps and helps them stay hydrated through dry winter spells.
One year, I forgot to mulch a new lilac I had planted, and the roots suffered due to the freeze-thaw cycle of the soil.
After that, I never skipped this step again, and all my lilacs have come through winter healthier ever since.
Water Deeply Before the Ground Freezes
Even though lilacs are fairly drought-tolerant, they need a good drink before winter sets in.
In September, as temperatures begin to cool, give your lilacs a deep watering to help their roots stay hydrated through the winter months.
This is particularly important if you’ve had a dry summer or early fall.
Lilacs need water to store energy in their roots for the next growing season, and going into winter with dry soil can make it harder for the plant to bounce back in spring.
In my garden, I make sure to water my lilacs deeply once a week in September, especially if we haven’t had much rain.
I focus on soaking the root zone to encourage the roots to grow deeper, which helps the plant withstand winter stress.
Years ago, I noticed that the lilacs I didn’t water before winter had a harder time coming back in the spring compared to those I gave extra attention to in the fall.
Since then, a good deep watering before the first frost has become a key part of my fall routine.
Protect Your Lilacs from Frost Heaving
One of the biggest challenges for lilacs in colder climates is frost heaving.
This occurs when the ground repeatedly freezes and thaws, causing the soil to expand and contract, which can push plant roots to the surface.
If the roots are exposed during winter, they can dry out or freeze, damaging the plant.
To protect against frost heaving, make sure your lilacs are well-mulched as described earlier.
The mulch helps insulate the soil and keeps the ground from freezing and thawing too quickly.
In particularly cold areas, you may also want to consider adding an additional layer of mulch or even covering the base of the plant with burlap or other insulating materials once the ground has frozen.
One winter, I lost a young lilac to frost heaving because I hadn’t mulched deeply enough around its base.
The roots were pushed up and exposed to the cold, and the plant didn’t recover the following spring.
Since then, I’ve made sure to provide extra protection for my more vulnerable lilacs, and I haven’t had any issues with frost heaving since.
Watch Out for Pests
Even in September, pests like borers, scale, and aphids can still pose a threat to your lilacs.
While lilacs are relatively hardy when it comes to pests, infestations left unchecked can weaken the plant, making it more susceptible to winter damage.
Inspect your lilacs for signs of pest activity, such as holes in the stems, sticky residue on the leaves, or discolored foliage.
If you notice any issues, treat the plant with an appropriate pesticide or organic remedy before winter sets in.
In my experience, dealing with pests early in the fall can prevent bigger problems down the road.
I had an issue with scale insects on one of my lilacs a few years ago, and by catching it in September, I was able to treat it before the plant was further stressed by winter.
To prevent recurring pest problems, I also make sure to keep the area around my lilacs clean and free of fallen leaves or debris, which can attract insects.
Regular inspections and maintenance go a long way in keeping your lilacs healthy year-round.
Avoid Fertilizing in the Fall
Fertilizing lilacs in the fall can do more harm than good.
While it might seem like a good idea to give your plants a nutrient boost before winter, adding fertilizer too late in the season can encourage new growth that won’t have time to harden off before the cold sets in.
Any tender new growth that appears in response to fall fertilization will be more susceptible to frost damage, which can weaken the plant overall.
Instead, focus on fertilizing in the spring, when the plant is actively growing and can benefit from the extra nutrients.
I learned this lesson the hard way when I fertilized one of my lilacs late in the season, and the new shoots were quickly damaged by frost.
Since then, I avoid fertilizing in the fall, and I’ve noticed my lilacs are much stronger and better able to handle the winter months.
Consider Wind Protection
If you live in an area with harsh winter winds, your lilacs may benefit from some added protection.
Strong, cold winds can dry out the branches and cause damage, especially to younger or more exposed plants.
One way to protect your lilacs from wind damage is to plant them in a sheltered location, such as near a fence or wall.
If that’s not an option, you can create a temporary windbreak using burlap, stakes, or even evergreen boughs.
In my own garden, I’ve found that lilacs planted in more exposed areas often struggle with wind damage, especially during particularly cold winters.
After losing a few branches to high winds one winter, I started using burlap wraps around my younger lilacs, and it made a noticeable difference in how well they survived the season.
For older, well-established lilacs, wind protection may not be as necessary, but for new plantings or smaller shrubs, it can be a lifesaver during especially windy winters.
Remove Dead Leaves and Debris
As you prepare your lilacs for winter, take the time to clean up any dead leaves or debris that have collected around the base of the plant.
This helps prevent fungal diseases and reduces the likelihood of pests finding a cozy spot to overwinter.
I always make it a point to rake up the leaves around my lilacs in September, especially if they’ve started to accumulate after a windy fall day.
Leaving dead leaves around the base of the plant can create a damp environment, which encourages the growth of fungi or mold that can harm your lilacs over the winter.
By keeping the area clean, you’re giving your lilacs the best chance to stay healthy and strong through the colder months.
Consider Transplanting or Dividing
If you’ve been thinking about transplanting or dividing your lilacs, September is an ideal time to do it.
Transplanting in the fall gives the plant time to settle into its new location before winter, while the cooler temperatures reduce the risk of transplant shock.
I’ve had great success with transplanting lilacs in the fall.
Use a sharp spade to dig up the plant, making sure to get as much of the root system as possible.
Replant the lilac in its new spot, water it well, and apply a layer of mulch to help protect the roots through the winter.
If you’re dividing an older lilac, make sure each section you divide has a healthy portion of the root system and a few stems.
This gives each new plant the best chance of survival.
Dividing lilacs is a great way to propagate more plants for your garden or to share with friends and family.
I’ve found that fall is the perfect time to do this, as the cooler weather helps the newly divided plants establish themselves before going dormant for the winter.
Final Thoughts
Preparing your lilacs for winter in September is all about ensuring they have the protection and care they need to survive the colder months and come back strong in the spring.
By focusing on light pruning, deep watering, mulching, and protecting your plants from frost, wind, and pests, you’re setting them up for success.
From my own experience, I’ve seen how a little extra care in the fall can lead to healthier, more vibrant lilacs when the growing season begins again.
Taking the time to follow these steps will not only help your lilacs survive the winter but also ensure they thrive for years to come.
So, as September rolls in, take some time to get your lilacs ready for the colder months.
They’ll reward you with their stunning blooms and sweet fragrance when spring arrives once more.
Happy gardening!