Solid fuel, candle-type heaters have been tested to determine their effectiveness when used, both under trees and in the open, to protect against freezing damage in a citrus orchard. Two heaters under each tree were found effective in increasing fruit temperatures under the tree by about 3°F, and heaters both under the tree and outside the tree more than doubled the temperature rise. Heaters placed outside the tree were less than half as effective as those under the tree in increasing fruit temperature—either for fruit inside the tree or for exposed fruit on the outside of the tree.