Cold Florida Nights
Florida usually has several days that the more tropical plants might be in danger. When the 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 are 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 your Horticulture Extension Agent and Master Gardener Volunteers. They 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 4905 George Blvd in the Bert J. Harris Jr. Agricultural Center by 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.
Planning for the weather and microclimates
Planning for cold weather starts with your plant selection and placement. Be careful not to overuse tender varieties so you can limit the number of plants you will need to protect. Learn where the protected areas of your yard are, and the places you can get away with putting those less cold hardy plants. These areas are called microclimates and can cover a few hundred square feet or large areas of terrain. Warm microclimates are on the south and east sides of lakes and bodies of water. A ditch full of water may be enough to create some heat. Southern and eastern sides of buildings can also be warmer as well as southern slopes and higher ground. Remember heat rises and cold settles. Get yourself a thermometer and place it in open areas in your landscaping. Local weather stations and website temperatures may vary from your home so you can compare your readings and theirs.
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 each year. These temperatures can be the most damaging depending on how tropical a plant is. A plant that might withstand frosts or mild freezes might not bear so well under these conditions and is extremely hard to protect.
Heating up the ground
My first suggestion when trying to protect your plants is to make sure the ground in the areas of the plants you are trying to protect is wet. Water as early as the day before a frost or freeze. The 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. Since plants don’t create heat, they will rely on the heat released from the ground to radiate up around the plants and help keep the temperature warmer. Don’t forget to shut your sprinklers off on the night of a freeze. Icing over your whole yard is generally a bad idea!
Dragging out the covers
Covering plants is probably the best method for the homeowner to trap the heat released from the ground. In the past gardeners dragged sheets and blankets out from their closets 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 to the ground and is secured to the ground ensuring 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 plants 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.
On extremely cold nights the heat radiating from the ground will eventually lessen. When this happens you can generate heat by keeping a water hose running under the covering in the form of soaker hoses or micro-irrigation 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.
Water dos and don’ts
Often in agricultural practices, water is used to protect plants from freezing. Citrus growers run micro-irrigation like mentioned above under the tree canopies to create heat. The canopies of the trees reflect heat toward 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 because standard residential sprinkler systems aren’t adequate for icing in. This method requires overhead irrigation and the 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 micro-irrigation under the canopy of plants to create 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 38 and 40 degrees Fahrenheit. You might have to stay up late but you’ll use a lot less water.
Frost instead of Freeze
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. Frost happens when ice forms on the ground, roofs, surface of plants and objects. It can happen when temperatures are in the high 30s and can form with air temperatures are below 38 degres.Be sure to remember 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 overhangs and tree canopies by reflecting the heat radiating from the ground back down.
Click here for FAWN Weather, the University of Florida’s Weather Website.
Good luck and stay warm.