While Oklahoma’s winter has been fairly mild for the most part, gardeners may be seeing some effects of the recent colder temperatures, especially on broadleaf evergreens.
Winter burn seems to be the most common, which occurs on such plants as azalea, boxwood, holly, magnolia, euonymus, nandina and viburnum, but it can affect narrow-leaved evergreens like pines and deciduous species, as well.
Often misdiagnosed as an infectious disease or damage from excessively cold temperatures, winter burn is caused from desiccation, which is a type of dehydration injury.
When roots are in dry or frozen soil, water lost through transpiration cannot be replenished by the roots and dehydration occurs. Water loss through transpiration is normally low during winter months, but it increases when plants are subjected to drying winds or are growing in warm sunny spots. Oklahoma’s winter weather certainly isn’t known for being consistent. As you’re aware, we can have bright, sunny days that almost feel like spring, or it can be cold and the winds are high, and both situations cause plants to dry out.
Symptoms of winter burn include scorching of leaf tips or outer leaf margins, complete browning of needles or browning from the needle tips downward or death of terminal buds and /or twigs.
Fortunately, broadleaf evergreens affected by winter burn likely will survive and send out new shoots and leaves this spring, depending on the severity of the damage. Where death of tips and/or small twigs has occurred, simply prune the plants back to live, undamaged tissue.
Gardeners have several options when trying to eliminate or at least minimize winter burns. The easiest method is to simply avoid planting broadleaved evergreens in areas of high wind exposure.
Another method is to deeply water plants during dry periods throughout winter months when temperatures remain above freezing for prolonged periods.
Gardeners also have the option of installing physical windbreaks. Burlap “walls” can help cut down wind and subsequent moisture loss to evergreen shrubs and small trees.
Antitranspirants of various types are available, but have shown limited success under Oklahoma’s climatic conditions.