Abstract
Abstract Thermal properties of tree wraps commonly used for freeze protection of young citrus trees were measured in the laboratory using a newly developed method to determine which factors are most important in wrap design and performance. Thermal diffusivity was lowest for wet fiberglass and styrofoam wraps with water containers attached to their inner surface, intermediate for dry fiberglass, and highest for thin-walled polyethylene and polystyrene wraps. Thermal diffusivity was inversely related to freeze protection capacity observed under field conditions for the tree wraps tested. Addition of water, either throughout the wrap material or in containers inside wraps, decreased thermal diffusivity three- and ten-fold, respectively. Minimum trunk temperatures of 2-year-old ‘Hamlin’ orange trees [ Citrus sinensis (L.) Osb.] were up to 2°C lower under ventilated tree wraps compared to similar nonventilated wraps on mild freeze nights. An ideal tree wrap should have low thermal diffusivity and lack free airspaces and ventilation holes, while allowing for gas exchange and expansion of the tree trunk.