Frost Damaged Plants May Need Pruning, but Wait until Spring
Recent freezing temperatures may have injured some citrus trees and other frost-sensitive plants. But since the full extent of injury won't be known for several months, UC Cooperative Extension (UCCE) horticulture advisor Ed Perry suggests gardeners wait until spring before pruning and removing damaged trees and plants.
The frost injury to plants depends upon a number of factors, including species, age, health, soil moisture and location. Frost injures plants by causing ice crystals to form in plant cells, making water unavailable to plant tissues and disrupting the movement of fluids. Frost-damaged leaves appear water-soaked, wither, and turn dark brown or black. Unprotected, sensitive young trees may be killed, but frost rarely kills mature trees in California.
"While you may be tempted to prune out damaged branches right away, it's best to wait until spring when new growth will show you the extent of the injury," said Perry. "Always allow plenty of time for new growth to take place, so that the damage is clearly defined. Earlier pruning often results in leaving some limbs which might continue to die back, and the removal of limbs which might recover."
If a one- or two-year-old grafted fruit tree has been killed almost to the ground, it's important to determine whether the dead wood extends below the bud union, something best done in April or later. "If only the roots survive and grow back, you may be left with an unproductive rootstock instead of the true-to-type fruit tree you originally planted. In this case, the tree should be replaced," Perry said. "If there is enough live wood above the bud union to grow a strong shoot, a new trunk will develop."
For herbaceous and shrubby plants, patience is also the best course. While you may be tempted to remove the damaged leaves, they provide some protection from future frosts. Wait til the danger of severe frost in your area has passed and new spring growth has begun before deciding what to prune or remove..
Courtesy of Jeannette Warnert, University of California Cooperative Extension