Cold damage to ornamental plants can be a problem during the winter in the Georgia landscape, although it seems unlikely here on the coast.
During the summer months, ornamental plants are actively growing and would be severely injured by even the slightest frost. During the late summer and early fall, the plants must prepare themselves for winter through a process called cold acclimation. This process is initiated by the cooler temperatures and shorter day lengths that naturally occur at this time of the year. Cold acclimation must occur in a timely fashion. If it occurs too early, the growing season of the plants will be shortened; if too late, they will be injured or killed by early frosts.
Typically, homeowners will notice the cold damage first on the leaves and stems. Ice forms within the plant’s cells, the plant tissue dies and leaves or stems become brownish-black and mushy. Plants that are not acclimated may sustain injury to the root system and may be severely damaged or killed.
Sometimes this is not noticed until the plant fails to leaf out the following spring. Damage to flower and leaf buds can occur during periods of low or fluctuating temperatures, such as we have been experiencing this week. This can lead to a reduction or total loss of blooms and damage of the foliage the following spring.
If you have ever noticed plants that normally bloom without blooms, frost damage could be the culprit. There is still time to help though. Protect plants in containers either by placing them inside a protective structure (house, garage, greenhouse or shed) or by placing a protective covering over them. Container plants are especially susceptible to cold temperatures; their roots are more exposed because they are above ground.
Plants with roots that are damaged by cold temperatures may not show immediate signs of damage; these plants will show signs of stress when temperatures rise and the demand for water from the roots is greater. Push together container plants that are left outside and mulch or cover them to decrease heat loss from the sides of the containers. Wrap the bases of the containers in plastic, burlap or blankets to reduce heat loss.
Plants growing close to the ground are usually protected by heat radiating from the soil. Tall, more open plants do not receive as much radiating heat and are not as protected from the cold. Mulching helps reduce heat loss of the soil, thus minimizing temperature fluctuations. Protecting the roots of tender perennials may also be beneficial for them to survive the cold and come back in the spring.
Covering your plants with sheets, blankets or cardboard boxes helps protect them from low temperature injury. However, plastic sheeting is not recommended as the plant can heat up rapidly as temperatures rise be damaged. Remove the cover and provide ventilation during the day to allow the release of the heat that is trapped by solar radiation.
Cold damage may not be apparent in the plant for several days or weeks. To determine if your plants have been damaged by the cold, wait several days after a freeze and remove several buds, stems and leaves, if present, from the plant. Use a sharp knife or razor blade to cut a cross section of the bud’s top. If there is any discoloration in the bud, they have been damaged. Waiting to prune after freezes have passed will guard against removing living wood. If localized damage has occurred to the foliage or stems, prune several inches below the injured tissue. Although injured buds may reduce or eliminate flowering or leaf emergence later this spring, no pruning is necessary.
Don’t forget to water. This hasn’t been a big problem for us here the past couple months, but plants continue to have water requirements during the winter and early spring months. Moist soil absorbs more heat, helping to maintain an elevated temperature around the plants.
Be sure to protect your plants during the coming cold snaps.
Richard Evans is the agriculture and natural resources agent for the Bryan County Cooperative Extension.