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Letter to the editor

It's time to get yard ready for frost

By MARY COLLISTER, Times Correspondent
Published December 20, 2007

Frost covers the flower on a weed in a yard in Clearwater as temperatures dipped into the 30s overnight in February 2006. December's not too soon to prepare your yard.
	[Jim Damaske | Times (2006)]

It's mid December, and the cold nights are just now starting to show up. Things could get worse, and it doesn't pay to be lethargic.

It takes just one cold (frosty) night, and many of the plants in the Tampa Bay area will not recover if they're not protected.

Now is the time to look at all the plants in your landscape. Do you have any that are susceptible to frost damage? If you are not sure, ask at the local garden center, use a good garden reference book, or search online.

Once you have identified those plants that may need protection from a cold snap, decide how you are going to provide coverings. When a freeze is imminent, there are a few things you can do to protect your plants.

Plants in containers should be moved into protective structures. This may be a covered lanai or garage. Move them back outside as soon as the weather allows.

Being in the garage or on the lanai usually drastically reduces the amount of light the plants receive.

Heavy mulch will help protect the roots of plants. Even if there is damage on the top growth, if the roots are healthy, the plant may recover.

Coverings protect more from frost than from extreme cold. Covers that extend to the ground and are not in contact with plant foliage can lessen cold injury by reducing radiant heat loss from the plant and the ground. Foliage in contact with the cover is often injured because of heat transfer from the foliage to the colder cover.

You can use cloth sheets, quilts, or black plastic. Remove plastic covers during the day or provide ventilation of trapped solar radiation. A light bulb under a cover is a simple method of providing heat to ornamental plants.

A method more often used by commercial growers than the home gardener is sprinkling with water. I do not recommend this for two reasons. First, there must be a clear understanding of how this method works. Sprinkling for cold protection helps keep the leaf surface temperatures near 32 degrees. It must begin as freezing weather is reached and continue until thawing is complete. It can also saturate the soil and cause root damage.

We never know which winter may bring frosts or freezing weather, so it's good to be prepared with the supplies we may need. My first few years in Florida, I carefully watched the winter weather reports, ready to cover plants when needed. Now I have decided that if a plant can't survive the winter, I'll replace it with something more appropriate. The only exceptions are my orchids. This "do or die" philosophy has led to fewer evenings out in the dark trying to cover plants and a hardier landscape.

The damage done, or not done, to plants is not based solely on the temperature of any given night. Temperature fluctuations and day lengths before a freeze affect the ability of plants to withstand freezing weather. A gradual decrease in temperatures over a period of time increases the ability of plants to withstand cold weather. A sudden temperature decrease usually results in more damage. Short periods of warmer weather in midwinter also make it more difficult for plants to adapt to cold weather.

There are some things that should be done long before a freeze to protect your landscape plants. The most important step is to select the proper plant for the proper location. The microclimate of a location is determined by factors such as elevation, landform, surface reflectivity, soil type, degree of canopy cover, and proximity of structures or other plants. Within your landscape you have many different microclimates. Be aware of these before choosing plant material.

Tender plants should be planted in an area with good air drainage, not in a low area where cold air settles. Arrange plantings, fencing, or other barriers to protect tender plants from cold winds.

Plants grown in optimal conditions are healthy and tolerate cold weather better. If injured by weather, recovery is quicker.

Apply fertilizer so that you don't get a flush of new growth right before cold weather arrives. New growth is more susceptible to injury.

Tree canopy covers can reduce cold injury caused by radiational freezes. These plants usually go dormant, or at least slow growth, earlier in the fall and remain dormant later in the spring. Canopies also elevate minimum night temperatures by reducing radiant heat loss from the ground.

Radiational freezes or frosts occur on calm, clear nights when heat radiates from the surfaces of objects into the environment. These surfaces can become colder than the air above them due to rapid loss of heat. When the air is moist, which is often the case here, this freeze deposits ice or frost on surfaces. Dry radiational freezes leave no ice deposits but can cause freeze damage.

Plant damage can be minimized be reducing radiant heat loss from plants and soil surfaces. You do this by covering your plants.

Wind breaks such as fences, buildings, adjacent plants and temporary coverings can protect plants from cold. They are especially helpful in reducing the effects of short advective freezes.

Advective freezes occur when cold air masses move from northern regions, causing a sudden drop in temperature. It is normally windy also. Radiant heat loss also occurs during an advective freeze, but the conditions are quite different from a radiational freeze.

Plant protection is more difficult because of the suddenness of the temperature drop.

Despite the beautiful weather we have had in recent weeks, it is necessary to be prepared for cold weather. It's better to be prepared and in possession of everything we need to protect our plants, than having to try and fabricate coverings after work one night in the dark.

[Last modified December 19, 2007, 21:37:17]