If you’re new to having lilacs in your garden or yard, you may feel a bit alarmed if you see the leaves falling off the plant in the winter. However, you can rest assured that this is natural and what the lilac is supposed to be doing during this time.
Lilacs lose their leaves in the winter because they are deciduous plants, which means the leaves fall off after they reach full maturity. This is a normal part of the lilac’s growth cycle.
In the rest of this article, I’ll explain more thoroughly why lilacs lose their leaves in the winter. I’ll also discuss some other reasons for leaf loss that you should be aware of.
Why Lilacs Shed Leaves in Winter
Deciduous plants, including lilacs, shed their leaves every year as part of their annual growth cycle. These plants lose their leaves in the fall or the winter after flowering. The leaves then naturally grow back during the growing season.
The term deciduous means “tending to fall off”, and the process of losing leaves is called abscission. This helps plants conserve their resources and survive the winter months.
The warm spring temperatures encourage new leaf buds on lilac plants to grow. As the temperature rises throughout the summer, the leaves continue to grow and develop until they reach maturity.
Then, as the temperature cools, the plants begin to shut down regular food production and deliver less chlorophyll to the plants. As a result, the leaves fall to the ground.
Other Reasons for Lilac Leaf Loss
It’s natural for lilac plants to experience leaf loss in the winter. However, if you notice your plant prematurely shedding leaves even during the growing season, the loss could indicate a potential problem. You must address this health issue to ensure your plant bounces back the following year.
Let’s take a look at some other reasons why a lilac plant might experience leaf loss.
Your Plant Is Infested With Pests
Unfortunately, dealing with pests is an unavoidable part of growing plants.
Let’s address some of the most common pests that affect lilac plants:
One pest that commonly infects lilacs is oystershell scales. These insects can grow up to 1/8th inch (0.3 cm) and cause extensive damage to the stems of lilacs. They can even cause the death of the plant if the issue is not addressed.
One way to get rid of oyster shell scales is to wrap some tape around any new growth, with the sticky side out. The oyster shell scales will emerge from their eggs and become stuck and unable to cause damage to the plant.
You can also try an insecticidal soap spray. It helps kill oyster shell scales and other insects and helps control black spots and powdery mildew.
Remove any diseased or dead parts of your lilac plant because this is where the pest colonies are most likely to live.
Another pest lilacs are susceptible to is ash-lilac borers. These creatures are the larva of a moth, and when they emerge from their eggs, they tend to bore through the wood of lilac. This kills the stems and causes leaves to fall.
The best way to deal with ash-lilac borers is to cut back infested branches all the way to the ground and burn them. If you leave the infected branches near the plant, the stubborn larva will find their way back to the lilac and continue killing stems.
For more information about cutting back lilac plants, read my other article: If You Cut Lilacs Will They Grow Back?
The Lilac Plant Is Diseased
Some plant diseases can cause a sudden falling of leaves.
Let’s discuss some of these common diseases:
One common disease that causes leaf loss is bacterial blight. This disease is typical in the common lilac, walnut, apple, pear, plum, and cherry plants. The disease is caused by the bacterium Pseudomonas syringae, which survives in diseased stem tissue.
Typically, this bacterium exists on the surface of plants and doesn’t cause them harm. However, when the bacterium enters stem tissue through a natural opening or a wound, infection occurs, putting your plant at risk.
Symptoms of bacterial blight include the following:
- Dark brown leaf spots with yellow halos
- Leaf curling
- Leaf twisting
- Black streaking on twigs
- Death of branch tips
- Death of blossoms
- Death of leaves
If you notice these symptoms, you’ll need to cut back the diseased branches and burn them. Afterward, disinfect your pruning shears so you won’t spread the disease again the next time you prune your lilacs.
Another disease that could cause lilac leaves to fall is powdery mildew. This fungal disease causes a layer of mildew to form on top of the leaves. This mildew looks like flour. If you notice a white substance on your leaves, it is most likely this disease.
Although mildew typically grows on the upper surface of the leaves, you should also regularly check the undersides. If you do notice powdery mildew on your plant, remove the infected branches and destroy them. Then, sterilize your pruning shears with rubbing alcohol or use a fungicide.
To prevent powdery mildew, ensure that your lilac plant is in a sunny area. Lilacs need at least six hours of sunlight a day anyway, and powdery mildew thrives in shadier areas. Regular pruning can also help prevent powdery mildew by increasing air circulation, and it also keeps your lilac plant at a reasonable size.
The Plant Is Suffering From Herbicide Damage
Herbicides are toxic to plants, and lilacs are especially sensitive. So, if your lilacs are exposed to herbicides, they can suffer damage that includes losing leaves.
Unfortunately, it is easy for a plant to accidentally be exposed to herbicides. With just a slight breeze, liquid herbicides can drift from where they were sprayed to nearby plants. Herbicides can also move from where they were applied to the root systems of other plants because of leaching or run-off.
Symptoms of herbicide damage include:
- Distortion and curling of leaves
- Twisted stems
- Leaf yellowing or browning
- Loss of leaves
- Stunted leaves in future seasons
- Plant death
Try washing the plant with water if you start to notice these symptoms and think they may be caused by herbicide damage. Be aware that water dilutes some herbicides, but it can also help soil-active herbicides to continue moving to where they don’t belong.
To combat soil-active herbicides, apply activated charcoal. Be sure that it does not contain any potentially harmful fillers, so you can be confident that you’re not causing further damage to your plant.
Another option is to completely remove the contaminated soil and replace it. This solution is only for drastic and extreme cases because doing this will be extremely expensive and time-consuming.
If you notice that your lilac plant is losing leaves around fall and winter time, don’t be alarmed. It is completely normal and natural for lilac plants to lose their leaves at this time because they are deciduous plants.
There are, however, other reasons a lilac may lose its leaves, and it helps to keep them in mind in case you notice leaf loss at another time of the year. That way, you may address the problem before it gets worse and ensure your lilacs come back healthily the following growing season.