An Energy-Conserving System for Orchard Cold Protection

The possibility of protecting an orchard against cold by enclosing it under a screen cover was studied in a preliminary field test. At the onset of freezing temperatures, water was sprinkled on the screen, forming a continuous sheet of thin ice. The screen and ice cover effectively reduced heat loss from the experimental enclosure. Simulated twig temperatures were 2-10°C warmer inside the enclosure during a variety of weather conditions, with outside air temperatures as low as —20°C. When outside air temperatures were —5°C, the inside simulated twig temperature could be held above the critical level for even tender blossoms by briefly sprinkling water under the screen at 10- to 15-min intervals. Although a screen cover and sprinkler system would be expensive to install, it could provide excellent cold protection and would be less expensive to operate than conventional orchard heaters and wind machines. Cooler daytime temperatures under the screen suggest the additional possibilities of dormancy control and reduced evapotranspiration