Beloved for their outstanding spring shows that feature pretty flowers with an intoxicating fragrance, lilacs handle chilly winters better than many perennial flowering shrubs.
Little is required to assist them through cold temperatures and many species and cultivars, including common lilacs, Syringa vulgaris, require cold weather to set flower buds.
A little prep work before frigid temperatures arrive can help prevent issues like damage or breakage from gnawing pests or heavy, wet snow.
And there are certain circumstances – like a late freeze – when proactive measures can help your lilacs avoid falling victim to bud kill.
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Dwarf lilac varieties in containers may also need some additional protection or a sheltered site if freezing temperatures and harsh conditions are common in your region.
Even the cultivars bred for warm climates have their own unique needs to survive winter and emerge in spring ready to flower and flourish.
If you’re wondering how to keep your showy shrubs healthy until next spring, let’s jump into how to winterize lilac shrubs!
Here’s a peek at what’s ahead:
How to Prepare Lilacs for Winter
Why Protect Cold Hardy Shrubs?
Common lilacs have excellent cold hardiness and are suitable for overwintering in USDA Hardiness Zones 3 to 7, although some cultivars are suitable for Zones 8 and 9.
Some cultivars of S. hyacinthiflora are hardy down to Zone 2, but many dwarf varieties are hardy only to Zone 5.
The term “cold hardiness” describes how low temperatures need to drop before a plant suffers damage.
The standard reference for North American gardens is the USDA Plant Hardiness Zone Map, with each Zone given a number based on the “average annual extreme minimum winter temperature.”
For Zone 3, that ranges from -40 to -30°F – so lilacs don’t need a lot of help to handle the cold!
However, there are rare occurrences when the shrubs might need a frost blanket to protect emerging buds from a late freeze. And they’ll appreciate a layer of mulch to keep the roots safe from heaving in freeze and thaw cycles.
Also, some preventative pruning can reduce the risk of limbs breaking under the weight of heavy snows or freezing rain.
Container grown lilacs are more prone to damage from cold weather and usually need a bit of attention before frosty temps arrive.
And don’t forget about the critters – herbivores like deer, rabbits, and voles can chew away the bark and tender tips if they’re hungry enough.
Also, the varieties bred for mild Zones 8 and 9, with low chill hour requirements may not have to deal with snow and extreme cold, but in areas with dry winters, they need to be watered regularly to prevent them from drying out.
Before we get into each of these scenarios, a few maintenance basics are helpful.
Before the ground freezes, clean up the beds or containers where your lilacs are growing, removing debris and litter – garden debris provides an ideal location for pests to overwinter.
Our guide to preparing the garden for winter discusses this and other tips for keeping plants safe.
Use a small rake to remove summer mulch, dead leaves, and any unwanted decaying plant matter.
If autumn rains have been insufficient, water your trees deeply before freezing temperatures set in – they’ll be much stronger and able to withstand harsh weather when they are well-hydrated.
Container Plants
Potted lilac plants can require additional protection during cold weather.
This is because the soil in containers and pots can freeze solid, causing damage to the roots.
Protect the Root Zone
To protect container-grown lilacs from freezing cold, add a four-inch layer of mulch over top of the root zone, using porous materials that don’t trap water such as bark, conifer needles, or straw.
And depending on how low your temperatures drop, wrapping the pots in bubble wrap or an old blanket can add an extra layer of insulation to keep the root zone from freezing.
Move to Shelter
Containers can also be moved into a sheltered spot to protect them from harsh winds and exposure to the elements.
Sites that often stay a couple of degrees warmer than open areas include against the exterior wall of a heated house, under evergreens, or tucked into a corner by a fence.
Bury Containers
If your winters are very cold, another option is to bury your potted lilac. To do this, the pot needs to be made of a material that can handle freezing temperatures, such as resin or plastic.
Natural materials like terra cotta or glazed ceramics are usually too delicate to bury in the garden and are unlikely to withstand freezing temperatures.
For more info on tough, weather-resistant materials, check out our guide to the best materials for containers, pots, and planters.
To bury container plants, choose a sheltered spot in the garden, and dig a hole a few inches wider than the pot.
If the container is large, it may not be possible to bury it entirely, but try to get at least half of it below the soil.
Fill the gap between the soil and pot with a thick mound of bark mulch, evergreen boughs, leaves, or straw, then mound the mulch materials up the pot’s sides and over the soil line, covering the lilac’s crown as well – aim for an insulating layer of six to eight inches.
When the worst of the cold weather has passed, pull the insulation back from the crown.
As the warm temperatures of spring approach, remove the remaining coverings, return your containers to their growing site, and water deeply if needed.
Unheated Storage
A final option is to move your containers into an unheated building after the first hard frost, such as a garage, greenhouse, or shed. Check the soil’s moisture monthly and water as needed.
Bear in mind that most lilac varieties require a number of chill hours to set flower buds, so they should never be brought indoors to a heated location.
Chill hours is the time a plant spends below 45°F – most hybrids of S. vulgaris require around 2,000 chill hours while the newer cultivars with low chill requirements need only about 500 hours.
Pots overwintered in a garage or shed should be moved back outside a few weeks before the last average frost date for your region.
If you have a lot of containers to move each year, consider picking up a sturdy plant caddy to ease your workload.
In-Ground Care
Although they’re well-equipped to handle cold weather, lilacs can suffer damage from desiccating winds, freeze and thaw cycles that heave roots, damage from heavy snows and freezing rain, or a bud-killing late freeze.
Prevent Desiccation
The most effective way to prevent desiccation is to grow your lilacs in a location protected from prevailing winds.
Being deciduous, the leaves aren’t damaged from drying winds but tender tips and branches can die off.
The shrubs should be well-hydrated before the ground freezes because drought-stressed plants are more susceptible to cold damage, particularly newly planted specimens.
To help them combat the drying effects of freezing winds, water lilac shrubs deeply before the ground freezes – after the first light frost is good timing.
Protect from Freeze and Thaw Cycles
To help prevent the roots from heaving when exposed to freeze/thaw cycles, cover the root zone with three to six inches of mulch – thicker is better in very cold temperatures.
Spread the mulch out to the drip line and be sure to cover the shrub’s crown.
Use materials that are porous and don’t trap water, such as bark mulch, conifer needles, evergreen boughs, pebbles, or straw.
Prune Damaged Limbs
Although pruning isn’t needed for young lilac plants, it can help to prevent damage to well-established trees and shrubs.
Breakage to the branches of large, mature trees can sometimes occur from the weight of heavy, wet snow or freezing rain, causing limbs to collapse and break away from larger stems.
If heavy, wet snow and freezing rains are a regular occurrence, you can improve the weight-bearing ability of your shrubs by regularly pruning the tips of long, lanky stems every two to four years.
Pruning should only be done in late spring to early summer, shortly after flowering has finished – to prune at any other time results in bud loss the following year.
To keep your shrubs tidy and reduce the chance of breakage from weighted limbs, use clean, sharp shears to head back growth of branch tips by as much as one-third, cutting the stems at a 45° angle just above a healthy leaf node.
Our guide to growing lilacs has more details about how to prune your shrubs for vibrant floral displays.
Late Freeze
It sometimes happens during late winter or early spring that a cold snap with freezing temperatures can damage or kill off emerging flower buds – a major disappointment when it happens.
As lilacs are all about the flowers, a little extra work to protect the precious blooms is worth the effort!
To keep the buds healthy and avoid damage from a late freeze, before the cold temperatures arrive, cover the shrubs with sheets of burlap, frost protection fabric or bags, or an old sheet, secured in place with plant clips.
Avoid using sheets of polyurethane. If the plastic rests on the buds, it can conduct and transfer the cold temperatures, causing damage.
Remove protective covers as soon as the danger or freezing temperatures passes.
Harvest-Guard Plant Protection Bag
Frost protection bags made of spun polyester are available at Burpee.
Critter Guards
Insects aren’t usually a problem in freezing temperatures, but herbivores may come visiting in search of food.
Mice, rabbits, and voles often gnaw at trunks and stems to reach the layer of tender, moist tissue below the bark, and deer are likely to chew on tender tips.
If hungry herbivores are an issue, you may have to erect a physical barrier to protect plants like deer netting or hardware cloth.
Deer netting is made of durable polypropylene and is easy to set up around a tree’s perimeter with stakes or rebar, forming a fence to keep deer at bay.
Wire mesh comes in a roll and is easy to bend and manipulate to shape, making it a good choice to wrap around the trunks of trees to thwart the likes of mice, rabbits, and voles from damaging the bark.
Hardware Cloth
Rolls of hardware cloth with a one-half inch mesh are available at Tractor Supply.
Items like smelly deer repellent are also an option, which you can read up on in our guide to deer-proofing your yard.
Cultivars with Low Chill Requirements
With cultivars bred for areas with low chill requirements, plants drying out from a lack of water is the most common problem experienced in winter.
Although your temperatures might stay warm and mild, these plants still go dormant and stop actively growing – but they shouldn’t be allowed to dry out completely.
If your winters are typically dry or rainfall is inadequate, water your lilacs deeply on a monthly basis.
Cold Weather Champs
Common lilacs are cold weather champs, and readily handle freezing temperatures, snow, and general cold weather nastiness!
And while they require little assistance to survive frigid temperatures, you can do a few things to help them emerge unscathed from the harsh conditions of winter.
If autumn’s rainfall has been light, give them a long, deep drink before the ground freezes – well-hydrated plants are better equipped to handle harsh weather than those that are drought-stressed.
Give them a nice, thick layer of mulch to protect the roots from heaving, which can occur during freeze and thaw cycles. And keep them pruned to reduce the chance of breakage under heavy snows.
Add a frost blanket if a late freeze threatens flower buds, and don’t forget to protect them from hungry critters. If furry foragers are a problem, put up a deer fence or use hardware cloth to save your shrubs.
A few protective steps taken before the bad weather arrives is worth it when you see your lilacs loaded with fragrant flowers come spring!
Any particular winter problems your shrubs need help with? Tell us about it in the comments section below.
And for more lilac know-how, add these guides to your reading list next:
