Severe freezes can damage leaves, twigs and even kill entire citrus trees. Freeze damage to citrus occurs when water inside the fruit, leaves and twigs becomes ice and ruptures the cell membranes.
During the fall and winter, extended periods of cool weather prior to a freeze can allow citrus trees to harden and acclimate, and therefore withstand more cold weather than non-acclimated trees.
On the other hand, freeze damage is more severe when it follows a warm spell. Because new growth is more susceptible to freeze damage, do not do anything that stimulates new growth during the winter.
Symptoms of freeze damage
The evidence of freeze damage to citrus fruit is the presence of ice crystals in the fruit. Ice formation inside the fruit usually ruptures the juice sacs.
Within several days of warm weather after a freeze, water will be lost from the fruit, causing a reduction in its juice content.
Following severe freezes, mature fruit should be harvested as soon as possible to minimize losses due to excessive fruit drop and reduction in juice content.
Freezes cause the leaves to dry out, curl, turn brown and fall.
If twigs and wood have not been damaged severely, the leaves will rapidly shed.
If twigs or wood have been seriously damaged, the frozen leaves may remain attached on the tree for several weeks.
After a severe freeze, twig dieback can continue for a couple of years. Another sign of severe freeze damage is splitting of the bark.
The true extent of freeze damage to branches may not be clear within the first three months following a freeze. No attempt should be made to prune or even assess damage from freezes until at least the new spring flushes get fully expended and mature.
Care of freeze-damaged trees
• Pruning freeze-damaged wood
No pruning should be done until late in the spring or the summer after a freeze.
In early spring, freeze-damaged trees often produce new growth that soon dies back. Sufficient time should be given for the dying back to cease and for the new healthy growth to take place and fully expand.
Experience has shown that early pruning does not promote recovery and that delaying pruning to the proper time will save money.
• Irrigation and fertilization
When leaves are lost, evaporation from the tree canopy is greatly reduced. Therefore, the amount of water required should be reduced.
Over-irrigation will not result in rapid recovery, but may cause root damage. Normal irrigation should be practiced when trees regain their normal foliage development and canopy density.
Fertilization of freeze-damaged trees should also be reduced until the trees are back to their original size and their canopies are back to their original densities.