Florida usually has several days that your more tropical plants might be in danger. When frost is predicted you will want to protect your more sensitive plants. Identifying the plants in your yard that are sensitive is the first step and can be challenging. Trial and error is usually how people discover this but if you don’t want to find out through the school of hard knocks you might consider doing some
research. At your County Extension office you can find help from Master Gardeners that can point you in the right direction. Master Gardeners are volunteers who have been trained by the University of Florida’s Extension Service as an educator in their Environmental Horticulture Program. The Master Gardener help desk is located at the Bert J. Harris Jr. Agricultural Civic Center on US 27 south, Sebring. You can also seek help from your local nursery retailers when you’re purchasing your plants. Once you have identified which plants you need to protect it’s time to learn when and how it needs to be done.
Freezing temperatures of 32 degrees Fahrenheit or below for eight or more hours are rare in Florida and usually don’t occur more than a few times of year. These temperatures can be the most damaging because they can do actual damage within the leaves and stems of some plants. A plant that might withstand frosts or mild freezes might not bear so well under these conditions and is extremely hard to
My first suggestion to those trying to protect your plants is to make sure the ground in the areas of the plants you are trying to protect is wet as early as the day before or morning before a frost or freeze. Wet ground holds more heat than dry ground and if it is wet the day before the sun can warm up the soil for you. Water your plants the morning before a freeze and make sure you turn off your sprinklers during a freeze. Since plants don’t create heat like humans, they will rely on the heat released from the ground to radiate up around the plants and help keep the temperature warmer. Did I mention you want to shut your sprinklers off during the
Sprinklers left on during a freeze may result in frozen plants and broken limbs. Photo from IFAS Communications
freeze? It’s always pretty, to wake up to a frozen yard, but not so healthy for your plants.
“Water your plants the morning before a freeze and make sure you turn off your sprinklers during the freeze”
Covering plants is probably the best method for the homeowner to trap the heat released from the ground. In the past gardeners drug sheets and blanket out from their closet or garage to drape over their plants. That still works but there are also products on the market called frost cloth, specifically for covering plants. The material is light and can often be left on during the day for those occasions when
we can expect two or more days of frost in a row. It’s a good investment and if it is folded up dry and carefully stored it can be used for many years. Whatever material you use, make sure it drapes all the way to the ground and is secured to the ground insuring that you capture as much heat as possible. Plastic, although not recommended, will work but where the plant touches the plastic there
might be leaf burn or damage. I sometimes use large black plastic pots to cover smaller plant but a garbage can or a cardboard box also works. You’ll want to remove the plastic from your plants when the sun comes out, and the temperatures start to rise, so the plants don’t overheat and burn.
A senior laboratory technician at the University of Florida’s Research and Education Center in Live Oak, covers snapdragons to protect from extreme cold temperatures in the 20’s. Photo from IFAS Communications
On extremely cold nights the heat radiating from the ground will eventually subside. When this happens you can generate heat by keeping a water hose running under the covering or possibly using some incandescent light or string of lights under it. Be careful that the light isn’t touching the fabric and that the fabric is not flammable or the result could get ugly.
Often in agricultural practices water is used to protect plants from freezing. Citrus growers run micro-jets or small misters under the tree canopies to create heat. The canopies of the trees reflect heat back towards the ground and keep the temperatures within the canopy warmer. This can be done under a variety of small trees and shrubs to create heat. Strawberry growers use a process referred to as “icing in” to protect their crops. I don’t recommend this practice to the homeowner unless they know what they are doing and can afford the water bill and because standard residential sprinkler systems aren’t adequate for icing in. This method requires overhead irrigation and constant addition of water until all ice that formed has melted. It works because as water freezes heat is released. By water constantly freezing on the leaf surface the temperature of the surface stays just above 32 degrees. A better technique for the homeowner would be something along the lines of what the citrus growers do and run a hose or micro-jet irrigation under the canopy of plants or frost cloth to release heat during the night thus taking advantage of the release of heat without ice forming on the leaves. I recommend if you try this you don’t run the water until temperatures drop to about between 38 and 40 degrees Fahrenheit. You might have to stay up late but you’ll use a lot less water.
A grove manager checks for cold damage on citrus. Photo by IFAS Communications.
Frost can sometimes be as problematic to your plants as a freeze. The same techniques are used to protect your plants during a frost that you use during a freeze. Be sure to remember that on a still night frost will start to form at about 37 degrees Fahrenheit and the less breeze you have the more chance of having a harder frost. Wind or even a light breeze as well as cloud cover will usually stave off a
frost. Wind works by mixing the colder low ground air and the warmer upper air to keep the cold from settling in. Clouds work much like the frost cloth or shade from tree canopies by reflecting the heat radiating from the ground back down.
Planning for cold weather starts with your plant selection and placement. Be careful not to over use tender varieties to limit the amount of covering you will have to do. Learn where the protected areas of your yard are and the places you can get away putting those less cold hardy plants and tropical. Below is the University of Florida’s Weather Website. Good luck and stay warm.