Although citrus trees tend to grow in humid, temperate regions, on the rare occasion when the tree is subjected to freezing temperatures, citrus trees can be damaged. When this happens, according to the University of California, ice crystals form in the cells of the tree, stopping fluid movement within the plant and starving the cells. This occurs in the citrus fruit as well, drying it out and making it unsuitable for consumption. Pruning a citrus tree after frost is necessary to prevent disease.
Allow the tree several months to recover in warm weather to asses the extent of the tree damage. Examine the tree once leaves begin to form during the spring and early summer. Find the branches which are not producing new foliage or fruit.
Cut away branches that are dead and have been damaged by frost at the shoulder of the tree. This is the portion of the limb that sticks out from the trunk, making a small lump. Make a cut 6 inches along the bottom of the branch, about a third of the way through. Cut again on the top of the branch, several inches further out from the first cut. Saw into the branch until it breaks and falls. Remove the rest of the stump at the shoulder using a hand saw. Use pruning shears for the smaller branches.
Wait until the following year to do heavy pruning to give the citrus tree time to recover after the frost damage. This allows the tree to regain its full canopy.