Permanent wraps should be installed after planting and normally are removed when the trees are about 4 years old. A wide variety of wrap materials is available, including polyurethane, fiberglass, polyethylene and other synthetics. Most offer only a few degrees of protection. Improved wraps which incorporate a reservoir of heat-retaining liquid provide freeze protection comparable to that achieved with soil banks. During freezes, water is warmer than air temperature and can release radiant heat to the trees.
Additional heat is released when water freezes, thereby providing added cold protection.
Flood irrigation must be applied quickly and must be sustained throughout the freeze to provide protection. Problems of inadequate water availability, extended application time, saturated root zone and potential loss of acquired hardiness limit the practicality of flood irrigation for cold protection in most orchards. Moreover, concrete pipelines may break during irrigation under freeze conditions and water may not be available from irrigation districts during freezes. Slightly greater protection is provided at higher rates of 30 or 40 gallons per acre per minute. However, application must begin before air temperature reaches freezing and must be continued until air temperature rises above freezing.