Many plants are already budding, leafing out, or blooming due to the early warm spring temperatures. With temperatures dropping back down to freezing, damage from the cold may occur. Cold injury to plants occurs during the fall or spring when the temperature declines after a period of warm weather. Tender foliage suffers the most from cold injury. There are two types of cold damage that may occur. Frost happens when the temperature drops below 32 degrees Fahrenheit and ice crystals form on the plant’s surface. Freeze damage occurs from the water in plant cells expanding and freezing. 

Frost damage on plants is generally seen on the tips of the leaves or flowers. The edges of the leaves will be burnt, showing discoloration. Bloom and bud drops may occur from a frost, and this is detrimental to many of our fruit crops when a frost occurs after trees have started blooming. A frost advisory is announced by the National Weather service when temperatures drop below 36 degrees Fahrenheit. Chances of a frost occurring in spring generally end on April 21st. 

Damage to freezing is the most damaging to the plants. Most damage occurs when the sun starts rising, unthawing the water frozen in the plant cells too quickly, killing leaves and stems. Freezing is likely to occur when temperatures stay at 32 degrees Fahrenheit or colder. When weather stations observe these levels, a freeze is likely. When there is a freeze, ice forms and expands between the cell walls of the plants. Some plants have enough room in their cell walls to withstand some freezing during a period without having too much damage. However, when freeze damage does occur, it is irreversible and, in many cases, kills the entire plant. 

After damage occurs, do not be in a hurry to remove the damaged plants. Any pruning to correct the damage from a frost or freeze should be done after the full extent of the damage is determined. Damage may not appear right away and some cold damage may not appear for several months. Injury to herbaceous shoots may become visible in a few days, while older, more established plant material takes longer to show signs of damage. After a frost or freeze has happened, there is no need to apply additional fertilizer trying to help your plant recover. Plants will recover on their own time. Damaged branches that do not show new growth after a few months have passed from a freeze can be pruned. Cutting back foliage right after a freeze can encourage new growth to appear that may be at risk of also being damaged. However, any plant material that is dead, dying, or diseased can be removed at any time because it is not doing any good to the remaining part of the plant. 

Matthew Clay is Horticulture Agent for North Carolina Cooperative Extension in Wilkes County.