Winter can be an extremely stressful time for our trees and shrubs especially evergreens such as pines, hollies and hemlocks. As the ground freezes the roots are no longer able to take up water and so the leaves and stems are forced to sacrifice what remaining moisture they have to keep the plant alive. Unlike deciduous trees, evergreens can't protect themselves by shedding their leaves and this loss of water is very damaging to the long-term health of the plant and can even lead to its demise.
Anti-desiccants are products that are sprayed on the tree, forming a protective coating on the leaves and needles. In Northern Virginia and much of the Mid-Atlantic region one application in late fall or early winter is sufficient to ensure your trees will be protected throughout the coldest winter months. However, in areas with harsher winters a second application in February is often required. Thorough and proper coverage are essential and certain trees such as blue spruce should not be sprayed as they already have a natural protective film which may be damaged by the addition of chemicals. When used correctly, these products can greatly reduce water loss and keep your trees and shrubs healthy and green. Most anti desiccants, also called anti transpirants are biodegradable and will wash away over several months, so that by spring the coating is gone, and the plant can resume its normal functions.
Interesting fact; anti desiccants can also be used on Christmas trees and Jack o lanterns to keep them from drying out as well.