Your evergreens may be suffering from winter burn

Monitor broad-leaved evergreens, such as boxwood, rhododendron and holly, and needled evergreens, such as yew and arborvitae, for winter burn. Winter burn is a cultural condition that affects plants that do not lose their leaves over the winter.

Leaves turn yellow and then brown in response to specific weather conditions. Leaves do not actually burn but rather dry up. Salt spray from vehicle traffic can also damage foliage.

Symptoms of winter burn typically appear first in late winter and accelerate in early spring. Various conditions combine to cause leaves to dry out. Mild winter temperatures and warm winter sun prompt leaves to process water, which cannot be replaced if the ground is either frozen or very dry. Winter winds also contribute to the problem.

Winter burn is common after extremely cold and extremely mild winters, and in both cases, it is exacerbated by lack of snow or rain in combination with strong winds and abundant sun.

It is best to wait until new growth appears in many situations before pruning out damaged areas if you are not sure whether the sections are completely dead. I have seen boxwood with an overall brownish-yellow cast in very early spring that completely greened up later in the season. In general, it is a good idea to plant broad-leaved evergreens where they will have some protection from winter sun and wind.

• March is a good month to control insects such as magnolia scale with an application of dormant oil. Verify that you have a problem insect before pursuing any controls and avoid applying treatments just to make sure there will not be insects present.

Temperatures should be at least 40 degrees Fahrenheit with no chance of freezing or rain within the following 24 hours. Avoid spraying on windy days to prevent any drift of the spray. As with any product, be sure to read the label to make sure the plants you are treating will not be damaged by the dormant oil spray.

Dormant oils can be very effective with minimal impact on the environment when used properly.

• Prune fruit trees and grapes as the worst of the winter cold has passed and spring growth has not yet begun.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.