Most of us look forward to the cooler temperatures and certainly less humidity that comes each fall. While last winter was cold but rather mild, past winters have had very cold temperatures resulting in the dieback of certain herbaceous, woody plants, as well as palms and tropical plants which are not hardy in our Sumter County 9A hardiness zone. There are ways to select and protect plants, as well as ways to minimize damage of potentially tender plants. Cold that falls over time lets plants acclimate to the colder temperatures which can result in less cold damage. It is the rapid temperature drops that causes the most damage to plant tissues by frost or freezing. January and February can be our coldest months.
Cold damage to plants can result from two types of events. Radiational freeze or frost happens on clear nights when the heat radiates up into the atmosphere leaving surfaces colder resulting in frost or freezes. These happen when there is moist air present. Advective freezes are caused when a cold air mass moves in creating a sudden drop in temperature. It is more difficult to protect plants from advective freezes. Wind brings very cold dry air which can move around the plants and freeze plant tissues. There are a few options you can use in your landscape to ensure reduced or no damage to your plants.
Choose Hardy, Healthy Plants. Pick plants that are hardy in our hardiness zone. By choosing plants that
have USDA Hardiness Zone 9A within its range of hardiness, you can be assured that these plants are suited for Sumter County. To choose plants in hardiness zones 9b through 10-11 may result in plant damage or death. If you have a few tender plants, you can plant them in microclimates where they receive some protection. Placing them under tree canopies or on the southern side of your home as well as near patios that hold and radiate heat can potentially result in plant survival.
Regularly scout your landscape plants for insects and disease. Healthy plants are more resilient to freeze or frost than those suffering from damage.
Pruning and Fertilization. Don’t prune plants in fall which can result in new, tender growth which may be damaged by radiational or advective freezes. Most fertilization of landscape plants should have been completed during their active growing season; so, don’t fertilize out of season which could also result in easily cold-damaged tender growth.
Protecting Plants. You can cover plants that you are concerned about being damaged. Often there are warnings for frost or freezes which should provide you time to cover your plants with blankets or sheets and weighting them to keep them in place. Remember not to use plastic as it can make the plants more susceptible to cold. You can use holiday lights to provide supplemental warmth to those plants, but don’t let the cover contact the lights. As things warm up, don’t forget to remove the fabric covers from your plants. You should also move container house plants from your landscape and lanai to garages, and mass container plants together and cover.
Water and Mulch. Before the freeze, you should water your landscape plants, then turn off your irrigation system. While members of the green industry such as fern farmers or some fruit growers may coat their crops with ice, they have the mechanism to ensure a consistent coating of ice to “warm” the crop. Coating ornamentals and turf with ice is not beneficial. Another option is to add 2-3 inches of organic mulch to protect plant roots from heat loss. Remember not to mulch up to the bark of trees and shrubs.
Hopefully this will help you prepare for protecting your plants during possible cold events this coming winter. For additional information on preparing your landscape for frost and freezes, read UF/IFAS Extension Publication, Cold Protection of Landscape Plants: http://edis.ifas.ufl.edu/mg025.