Article by Sylvia Durell
We love these low 60 degrees nights…but the nights that reach freezing temperatures means we need to put extra care toward our plants. Here in Hernando County, we often get temperatures that are low enough to cause injury to our outdoor plants. This is especially true if the plants were not planted according to the #1 Florida-Friendly Landscaping principle: Right Plant, Right Place. We often fall in love with tropical plants that are not suited to our area and put them at high risk for cold-injury. But even our “right” plants are occasionally damaged by a frost or freeze.
There are two kinds of freezes that occur; radiational and advective. Radiational freezes happen on windless, clear nights when heat radiates from objects including plants. Surfaces become colder than the air around them. If there is moisture in the air (high humidity), frost or ice accumulates on the surfaces and results in plant damage. When the air is dry (low-humidity), the low temperatures leave no frost but freeze damage can still occur. Covering your plants can help prevent radiant heat loss. Advective freezes occur when cold air masses, often accompanied by wind and rain, come in from northern regions and cause a sudden drop in our temperatures. Plant protection is more difficult as plant covers are not as effective. The weather conditions prior to a freeze can also impact the level of cold injury to plants. A gradual decrease in temperatures increases the ability of a plant to withstand cold. The plant acclimates, or becomes accustomed to the cold. A sudden, unexpected freeze often causes more damage than one which occurs after a period of increasingly cold weather. Here are some tips for improving your plant’s cold weather survival chances:
- Choose plants that do well in hardiness zone 9A.
- Be aware of microclimates. Some areas of our gardens are warmer, wetter or drier than surrounding areas. Don’t plant tender plants in a low area where cold air can settle.
- Use taller plantings, fences and buildings as windbreaks to help especially during advective freezes.
- Keep your plants healthy by giving them properly-timed nutrition. But don’t fertilize too late in the season. New growth is the most susceptible to damage.
- Make sure the soil has good drainage. Poorly drained soils cause weak, shallow roots that are susceptible to cold injury.
- Don’t prune after the middle of October. The tender new growth that has been encouraged will most likely freeze.
- Reduce radiant heat loss and protect plant roots by mulching around the plants.
- Slightly moisten the soil around your plants in the late afternoon before a freeze or near-freeze. Moist soil releases more heat than dry soil.
- Don’t run your irrigation system all night like you see commercial growers doing. The heat that is released from the continuous action of water freezing on plants and is what keeps plant cell temperatures above freezing. Our irrigation systems are programmed to move on to another zone, which stops the heat production and sets the plants up to freeze.
- Cover with sheets, quilts or purchased frost/freeze cloth not plastic. Cover before the sun goes down to capture heat from the soil. The covering must extend to the ground to keep the heat in. Stake or weigh the cloth down. Cardboard boxes can also be used. Remove covers during daylight. Freeze/frost cloth can remain on several days.
For more information, call Sylvia Durell, Hernando County Florida-Friendly Landscaping Program Coordinator at (352) 540-6230 or the UF/Master Gardeners at (352) 754-4433.
About the Author: Sylvia Durell is the Hernando County Florida-Friendly Landscaping™ (FFL) Program Coordinator. Her position is funded by the Hernando County Utilities Department. She is a Certified Horticulture Professional through the Florida Nursery, Growers and Landscape Association. Ms. Durell is available for presentations to clubs and for “brown bag” lunch programs for employees of Hernando County companies. Call (352) 540-6230 for a list of topics.