Photo by Tulay Emekli.
Early spring is a time we see a lot of evergreen shrubs and trees that have seen better days. A common question we get when we go to look at a potential landscaping client’s space is “Why are my evergreens turning brown? They’re supposed to be evergreen, right?” Browning of evergreen foliage during and shortly after the winter months occurs for four reasons.
Winter Sun & Wind
Winter sun and wind cause water loss while the roots are in frozen soil and unable to take up water from the ground and replace lost water. This results in desiccation and browning of the plants.
Unseasonably Warm Days
Bright sunny days during the winter also cause warming temperatures which in turn initiates cellular activity. Then, when the sun is quickly shaded, temperature drops to injurious levels and the foliage is injured or killed.
Sunny & Cold Days
During bright, cold winter days, chlorophyll in the foliage is destroyed (photo-oxidized) and is not resynthesized when temperatures are below 28° F. This results in a bleaching of the foliage.
Unseasonably Cold Days in the Fall or Late Spring
Cold temperatures early in the fall before plants have hardened off completely or late spring after new growth has occurred can result in injury. Damage normally occurs on the south, southwest, and windward sides of the plant, but in severe cases the whole plant may be affected. Yew, arborvitae, and hemlock are most susceptible, but winter browning can affect all evergreens. New transplants or plants with succulent, late season growth are particularly sensitive.
How Do I Prevent Damage?
There are several ways to minimize winter injury to evergreens. The first is proper placement of evergreens in the landscape. Yew, hemlock, and arborvitae should not be planted on south or southwest sides of buildings or in highly exposed (windy, sunny) places.
Also winter injury can often be prevented by constructing a barrier of burlap on the south, southwest, and windward sides of evergreens . If a plant has exhibited injury on all sides, surround it with a barrier, but leave the top open to allow for some air and light penetration.
Keeping evergreens properly watered throughout the growing season and into the fall is another way to reduce winter injury. Never stress plants by under- or overwatering. Decrease watering slightly in September to encourage hardening off, then water thoroughly in October until freeze-up. Watering only in late fall does not help reduce injury.
If an evergreen has suffered winter injury, wait until mid-spring before pruning out injured foliage. Brown foliage is most likely dead and will not green up, but the buds, which are more cold hardy than foliage, will often grow and fill in areas where brown foliage was removed. If the buds have not survived, prune dead branches back to living tissue. Fertilize injured plants in early spring and water them well throughout the season. Provide appropriate protection the following winter.