Citrus trees provide a gardener with fragrant blossoms and fresh fruit. While container citrus trees can be moved into a garage or indoors during wintertime, trees grown in the ground may require protection to prevent cold damage. Excessive cold damage can kill your citrus tree, but many trees that experience slight damage can recover and continue to produce.
Citrus trees that suffer cold damage or frost damage display symptoms of this damage on the bark and shoots. If the frost damaged leaves on your citrus tree, they will turn brown and fall off on their own. The wood will discolor and appear to be dead. Bark may swell and appear to separate from the tree if it's been damaged.
The only care a gardener can provide for citrus trees that have received cold damage is to prune away the damaged areas. The University of Arizona recommends waiting until your tree begins to grow again before pruning, since some shoots that appear to be dead may actually grow again. Prune the damaged growth when frost danger passes and your tree starts to grow, using anvil pruners.
Protecting Young Trees
Young citrus trees require more protection than old ones, since they aren't yet established. To keep your young citrus tree alive in a cold winter, string the branches of the tree with Christmas lights. Plug the lights into an outdoor outlet on cold nights to add a few degrees of warmth. Supplement this by wrapping the tree with burlap or with a breathable tree wrap. Pin the layers of the wrap or burlap together and wrap the tree's trunk and branches altogether. When frost danger passes remove the tree wrap.
Protecting Mature Trees
Wrapping the mature tree with Christmas lights will also help protect it. Gardeners may use one of several short-term protection methods to keep a mature tree from getting damaged in frost. Mound soil up along the trunk of the tree so the trunk becomes buried; this will keep the trunk from getting damage. Set up a fuel-powered space heater and leave the heater blowing overnight toward the citrus tree to keep it warm in an emergency.
Gardeners can also set up a sprinkler that sprays water over the branches and trunk of the citrus tree. As the water turns into ice, this creates energy which keeps the tree warm enough to repel damage. However, this method can't be combined with any of the above methods that require the use of electricity or fuel.
Gardeners in cold areas should prevent cold damage by choosing a citrus tree that's hardy. Meyer lemons are hardier than standard lemons; satsumas and tangerines are hardier than oranges; and kumquats are especially cold-hardy. The University of Florida maintains a list of cold-hardy varieties recommended for planting in areas that receive frost (see Resources).