It is possible to give some protection to blossoms from freezing by covering the tree with a bed spread, blanket or similar fabric but the material should reach the ground so that heat given off from the soil is captured. Old-fashioned Christmas lights distributed through the tree will help to give added protection. The newer, smaller Christmas lights do not give off enough heat and are not recommended. Of course the practicality of this method of protection depends upon the size and number of trees and access to electricity.
Sprinkling the tree with water throughout the freezing period can also protect the blossoms but is a dangerous option. Sprinklers should be started before the temperature drops to freezing to be sure ice does not block the garden hose or water line. Continue until the temperature warms. With this protection method, there is the potential of creating an ice storm. If temperatures remain below freezing for several hours, ice will accumulate on the branches and limbs. The weight from the ice may cause branches and limbs to break causing severe, and possibly permanent, damage to the tree structure. Also, if water drainage from the soil is slow and the water displaces oxygen from the roots, damage to trees may result. (Ward Upham)