When outer needles of evergreen trees and leaves on broadleaf evergreens turn brown, especially on the west and southwest sides of these plants that face the sun, it’s often from winter burn. Low-growing plants like creeping juniper or cotoneaster which don’t have a shaded side may have winter burn across the whole plant.
As the name suggests, the south and south-west facing sides of plants exposed to the winter sun are “burned” when the plants transpire and lose moisture beyond what has been replaced. The condition applies to all elevations, but introduced landscape plants at 7,000 to 8,000 ft. elevations may be more stressed due to more solar radiation and colder temps. Newly installed plants are often more susceptible because their root systems are not as fully developed as more mature plants.
Also be aware that there are other conditions that lead to browning plants that are not winter burn.
- Salt damage from ice melt products can damage plants. Remove any product residue and try to flush residue out of the soil.
- Spider mites are a common infestation on junipers. The mites suck the moisture out of the plants and lead to browning. If you suspect spider mites, consult with a pro who can give advice on treatment options.
- Junipers are also susceptible to damage from voles – rodents that often nest in junipers. Vole damage, however, usually involves browning deep within the plant – not just on the edges – because voles chew inner branches.
- Transplant shock may also cause plants to turn brown and in this case, what you should do for the plants is the same as for winter burn.
Coping with winter burn
Winter burn damage cannot be undone, but there are still steps you can take to bring plants back to good health:
- Water now if the soil around the plants is dry. Continue to check moisture and water as needed, without over watering.
- Prune away dead or seriously damaged branches – but don’t overdue it. Brown leaves on broadleaf evergreens don’t necessarily mean the whole branch is dead. Pay attention to where new growth emerges as the new buds appear and take care not to prune away the new growth.
- While winter burned plants can be fertilized, wait to apply fertilizer until the plants are starting to grow again – not while they are mostly dormant.
As with most plant health issues, the best treatment protocol is prevention. In April, it’s too late to prevent winter damage, but knowing what to do going forward is still useful information.
- Select healthy plants to begin with.
- Install plants as early in the growing season as possible. This gives them more time to establish roots and mature before the dormant season. That maturity provides them more vitality to help them through the winter.
- Make sure plants are well-watered going into the winter and check the soil moisture periodically during the winter months and water when it’s dry.
As we begin a new growing season, keep in mind that many plant problems can be eliminated or reduced through proper ongoing care. Healthy plants are the most pest and disease resistant which means they require less time, effort and expense for remedial care in the long run.