The reason for your lilac dying is usually because the soil drains too slowly for the lilac to tolerate. Lilacs require well draining soil, and if the soil is waterlogged around the roots this promotes the conditions for root rot and Verticillium wilt which causes the leaves to turn brown and drop off with a dying appearance.
The most common reasons for a lilac dying are:
- Waterlogged soil (promotes the conditions for fungal diseases).
- Drought stress after planting.
- Not enough direct sunlight.
- Soil is too acidic (lilacs prefer alkaline soils).
- Climate too hot and high humidity.
- Lilac borers (insect larvae) cause wilting leaves dying branches.
Keep reading for exactly why your lilac is dying and how to save it…
Waterlogged Soil Causing Dying Lilac
Lilacs naturally grow in chalky soils and in hilly locations in their native Balkan peninsula. In this environment the soil is evenly moist at the roots yet well draining, so that the roots do not become waterlogged.
If the lilac’s root are in waterlogged soil then this promotes the conditions for fungal disease pathogens which prevent the lilacs roots uptaking moisture and nutrients, causing the leaves to turn yellow or brown with a dying appearance.
Waterlogged soil also excludes oxygen from the soil which interferes with roots respiration and also prevents the roots from uptaking nutrients causing the lilac to die back.
Saturated soil is usually as a result of clay soils that drain too slowly or naturally boggy low lying areas of the garden, both of which can result in a dying lilac shrub.
Lilacs are more sensitive to slow draining or water logged soils then most shrubs.
However if you amend the conditions before fungal disease such as root rot or vertiuclum wilt set in then the shrub can be saved.
How to Save it:
The key to saving the shrub is to move the lilac to a conditions of more favorable drainage that mimic the well draining conditions in the lilacs native environment.
To do this I recommend transplanting your lilac as a matter of urgency from any soil that drains slowly and is naturally boggy.
Find an area of the garden that has more preferable drainage conditions (perhaps on a slope) and amend the planting area with lots of organic matter (compost, leaf mold or well rotted manure) as well as some horticultural grit or sand which helps to improve the soils structure and increase drainage.
If the lilac has been in slow draining soil for a short time then there is a good chance the lilac can be saved once it is in well draining soil that replicates its natural conditions.
However if the lilac has been in saturated soil for too long then root rot and various fungal disease pathogens are likely to prevent the lilac from uptaking nutrients at which point lilac branches are likely dying back and it can be very difficult to save.
Soil is Too Dry (Lilac Dying After Planting)
Lilacs require the soil to be evenly and consistently moist after planting yet also well draining, so that the roots are not sat in waterlogged soil.
This is particularly important after planting a lilac shrub as it can take some time for their roots to adjust to the new soil so that they can draw up water efficiently at which point they are most at risk of dying.
Mature lilacs (any shrub exceeding 3 years old) are far less likely to suffer drought stress due to their extensive roots, unless there are drought conditions or the soil is particularly sandy or stony and drains quickly.
Symptoms of a drought stressed lilac are leaves that wilt, turn brown or yellow and fall off.
How to Save it:
They way to save a drought stress lilac is to first ensure that you have prepared the soil well prior to planted by adding lots organic matter to the soil.
Materials such as compost, leaf mold or well rotted manure retain moisture around the roots to mitigate the drought stress, yet also have a porous structure that allow excess water to drain away (preventing root rot and fungal disease) and create the optimal soil conditions for lilacs.
If your lilac is planted in sandy soil then I recommend transplanting or temporarily easing it (gently with a fork) out the ground and amending the planting area by adding lots of compost to retain moisture.
Give the lilac a really good soak, ideally with a hose and then apply a 2 inch layer of mulch around the base of the shrub.
Mulch helps to conserve moisture and improves the soil’s structure, so that it is more favorable to the lilac.
Use a mulch made from compost, leaf mold or well rotted manure to help retain more moisture.
Always water with a generous soak as this encourage the roots to grow deep in the soil and establish properly so they can access moisture and nutrients and so they are more resistant to drought.
Not Enough Sunlight
The most common types of Lilacs (Syringa vulgari) grown in gardens are the world are native to rock areas and hilly locations in the Balkan peninsula in Southern Europe where they grow in relatively open areas without having to compete too much for sunlight.
Whilst you do not need a Southern European climate to grow lilacs (they are extremely cold hardy) it is essential that the lilac is in a location of full sun (more then 6 hours) for the lilac to grow and to flower.
Whilst lilacs can survive in some partial shade, they do not grow well in full shade with poor growth, fewer leaves and have a dying appearance.
Less light also increases the prevalence of powdery mildew which is a fugal disease that can appear on the leaves and bark as white to gray, powdery patches.
How to Save it:
If your lilac is in less then 6 hours of sunlight then consider either:
- Transplanting the tree to an area with at least 6 hours of sun.
- Cut back any overhanging tree limbs or near by shrubs that may be casting shade on your lilac.
This should help to revive your lilac and decrease the prevalence of powdery mildew as bright sunlight creates unfavorable conditions for the fungus.
Powdery mildew is not a serious threat to your lilac and it should improve with more light and better airflow.
(Read my article, why is my lilac not blooming).
The Soil is too Acidic
Lilacs grow naturally in chalk soils that tend to be either pH neutral (7) or slightly alkaline.
If the soil is too acidic then the acidity can prevent the root from uptaking certain nutrients from the soil which causes poor growth, yellow or brown leaves and a dying appearance.
Lilacs can grow in soil that is slightly acidic (pH 6) but if the soil is significantly more acidic then pH 6 then it is unlikely the lilac can grow in your garden.
If you are unsure of your soils pH level and suspect that soils acidity could be the cause of your dying then I recommend talking to someone who is garden savvy in your neighborhood as keen gardeners are likely to know whether the soil is particularly acidic in your area.
Or you can test the soil using a soil test kit from amazon, or even send a sample of your soil away to be tested (which is the most reliable way to accurately of determine the soils pH).
How to Save it:
If the soil is lower then pH 6 then this is likely the cause or at least contributing to the dying appearance of your lilac.
In this circumstance, I would recommend not growing lilacs and instead grow plants that are more suited to the specific pH of your garden (roses, camellias, rhododendrons and azaleas all grow well in acidic soil).
However it is possible to grow lilacs in acidic garden by either growing lilacs in a pot or amending the soil with agricultural lime (available from garden centers) which increase your soils pH from acidic (any pH value below 7) to either pH neutral (7) or alkaline (any pH value above 7).
Amending the soil is an ongoing process, so if possible I would grow a lilac in a pot as it is far easier to customize the soil characteristics to the preferences of the lilac rather then trying to adjust the characteristics of your garden soil.
Warm Temperatures and High Humidity
Lilacs are accustomed to the climate of the Balkan peninsula and prefers cold Winters and low humidity (once it is establish lilacs are one of the cold hardiest shrubs).
Climates that are too hot or too humid are contrary to the lilacs natural conditions in their native environment.
Humid conditions promote the conditions for fugal diseases and cause the leaves to wilt and branches to die back.
Lilacs often do not flower when they are grown in climates with mild Winters as they require a period of cold initiated dormancy to produce flowers and are best grown in USDA zones 3-7.
If you live in a hot climate with mild Winter and high levels of humidity, then its is less likely your lilac can flower or grow into a healthy shrub, so it is best to find other plants that are more appropriate for your climate.
Lilac Borers- Dying Lilac
Lilacs are common affected by powdery mildew which is usually not serious, however lilac borers are lavre of moths that bore into the lilac usually in the lower braces and leaves small entrance holes and sawdust as evidence of their attack.
Lilac borers cause the lilac’s leaves to wilt and branches to snap off with a dying appearance.
Once lilac borers are established they can be particularly difficult to get rid of.
To control the impact of lilac borers prune away the older branches as branches that are somewhat gnarled with more cracks provide more opportunity for the larvae to attack.
How to Save it:
The way to control lilac borers (which also affect ash trees and privet) is to use a lindane spray which is an insecticide for boring larvae.
Lindane spray is available from some garden centers although it is quite a specific product that may not be stocked at every garden center so it may be easier to buy online.
Lilacs that are healthy and live in good conditions (enough moisture, full sun etc.) are less resilient to insect attack, so a combination of good care practices of lilacs, cutting back affected branches is necessary and lindane spray can control the problem to help revive your lilac.
Key Takeaways:
- The reason for lilac shrubs dying is because of fungal disease due to slow draining soils. Lilacs require well draining soil to stay healthy and if the roots are in boggy soil then they are susceptible to root rot and other fungal diseases which cause the lilac leaves to turn brown and dying branches to drop off.
- Newly planted lilac shrubs can die back if the soil is too dry. Lilac requires evenly moist, yet well draining soil to thrive. If the soil is too dry or too sandy then the roots cannot uptake enough moisture which causes the leaves to wilt with a dying appearance.
- Lilacs grow in the open environments with full sun. If the lilac is planted in a shaded garden then this results in poor growth with fewer flower and the leaves can turn yellow with a dying appearance.
- Lilacs are native to the Balkan peninsula and typically grow in pH neutral or alkaline soils. If the soil is too acidic then the lilacs roots cannot uptake certain nutrients which causes the leaves to turn yellow and brown with poor growth and a dying appearance.
- Lilacs grow in climates with cold Winters and low humidity and grow best in gardens that are in USDA zones 3-7. If the Winter is too mild or the climate is consistently humid then this is contrary to the conditions to which the lilac has adapted and results in fewer flowers, poor growth and greater risk of fungal diseases.
- Lilac borers are insect larvae that create small holes in the lilacs wood and produce sawdust. Lilac borers cause the leaves to wilt and dying stems to break off.
- To save a dying lilac, create the conditions of the lilacs natural environment by transplanting the lilac to soil that is well draining yet retains moisture with an alkaline soil pH and in full sun. Cut away any dying branches back to the base to stimulate new growth. If there is evidence of lilac borers apply lindane spray.