Chlorophyll is the substance that gives plants their green color and is necessary for plants to convert carbon dioxide from the air into oxygen. When temperatures are below 28 degrees, the chlorophyll is no longer produced. This results in a bleached appearance of the foliage. Cold temperatures can also be detrimental to plants that have not been hardened off completely in the fall or to plants that experience late spring growth. Foliar damage normally occurs on the south and windward sides of the plant, but in extreme cases the whole plant may be affected.
All evergreens can experience winter browning.
Yew and arborvitae are the most susceptible to winter damage, and therefore should not be placed on the southside of buildings or windy, sunny places. To help prevent winter injury, burlap can be placed as a barrier on the south and windward sides of evergreens. Proper watering can also help eliminate winter injury. Water throughout the growing season and into the fall. Encourage hardening off in September and October by decreasing the amount of water.