by Linda Foster Benedict, LSU AgCenter contributor
LSU AgCenter horticulturist Dan Gill offers suggestions to protect your landscape plants before a freeze.
First, make sure they are well-watered, Gill said, because this may help them better deal with the cold.
"Many times cold weather is accompanied by strong, dry winds. These winds may cause damage by drying plants out and watering helps to prevent this," Gill said.
Wetting the foliage of plants before a freeze does not, however, provide any cold protection. Neither will a layer of ice protect plants, once the water is turned off. A spray of water must continue through the entire freezing period for it to provide protection, Gill said.
Move all tender plants in containers and hanging baskets into buildings where the temperature will stay above freezing. If this is not possible, group all container plants in a protected area, such as the inside corner of a covered patio, and cover them with plastic.
"If plants are kept inside for extended periods, make sure they receive as much light as possible," Gill said.
For plants growing in the ground, mulches can help protect them, Gill said. Use a loose, dry material such as pine straw or leaves.
"Mulches will only protect what they cover. Mulch at the base of a bird-of-paradise, for example, will help the roots but will provide no added protection to the leaves," Gill said.
Mulches are best used to protect below-ground parts or crowns, or they may be used to completely cover low growing plants to a depth of 4 inches.
"Leave mulch that completely covers plants in place no more than three or four days. Mulch at the base of a plant can remain in place all winter," Gill said.
If plants are not too large, individual plants can be protected by covering them with cardboard or Styrofoam boxes. Larger plants can be protected by covering them with fabric or plastic.
"Fabric coverings, such as sheets, can get wet and heavy if rains occur. Plastic would be better in rainy weather," Gill said.
However, wherever a leaf touches a plastic cover, it will freeze. Both of these issues can be resolved by providing simple supports under the cover to support wet fabric or keep a plastic cover from contacting the foliage. The structure holds the covering off the foliage, preventing branch breakage and improving cold protection.
"It need be nothing more elaborate than three stakes slightly taller than the plant driven into the ground. The cover should extend to the ground and be sealed with soil, stones or bricks," Gill said, adding that clear plastic covers should be vented or removed on sunny, warm days.
Gill said covers work best by preventing or blocking heat loss. However, with extreme, prolonged cold many plants will still die even with protection.
"This may be prevented by providing a heat source under the covering. A safe, easy way to do this is to generously wrap or drape the plant with small outdoor Christmas lights – not LED lights. The lights provide heat but do not get hot enough to burn the plant or cover. Please be careful and use only outdoor extension cords and sockets," he said.
If necessary, you may prune back a large plant, like a hibiscus, to make its size more practical to cover.
For trees too large to cover, such as palms and citrus, you may at least want to wrap the trunk with an insulating material such as foam rubber or blankets, Gill said.
"Even if the top dies, you may be able to regrow the tree from the surviving trunk," he said.
For palms, the trunk must be wrapped from ground level to the base of the leaves to protect the trunk and crown.
If you are growing vegetables, harvest any broccoli, cauliflower, fava beans or peas that are ready. Freezing temperatures will not hurt the plants but can damage the heads, pods and flowers. Also, any ripe citrus fruit should be harvested from the tree before a hard freeze.
After the freeze, move container plants back to their spots outside.
"Plants do not mind being moved in and out as needed through the winter," Gill said.
For plants that you covered, remove or vent clear plastic covers on plants to prevent excessive heat buildup if the next day is sunny and mild. You do not need to completely remove the cover if it will freeze again the next night. You may leave plants covered with blankets, sheets or black plastic for several days without harming them, but eventually the covers will need to be removed so they can get light, Gill said.
"Do not prune anything for a week or more after a freeze. It often takes a week or so for all of the damage to become evident," Gill said.
Damaged growth on herbaceous or nonwoody tropical plants, such as cannas, elephant ears, birds-of-paradise, begonias, impatiens, philodendron and gingers, may be pruned away back to living tissue.
"This pruning is optional and is done more to neaten things up than to benefit the plants. However, if the damaged tissue is oozy, mushy, slimy and foul smelling, it should be removed," Gill said.
If you don't prune before, be sure to cut back or prune these herbaceous tropicals in spring after the danger of freezes is past and before they make substantial new growth, Gill said.
You may remove the damaged foliage from banana trees but do not cut back the trunk unless you can tell for sure that it has been killed. The exception would be any banana trees that produced a bunch of fruit last year. They will not send up any more new growth and should be cut to the ground to make room for new shoots that will come up this summer, Gill said.
"Generally, it's a good idea to delay hard pruning of woody tropical plants, such as hibiscus, tibouchina, angel trumpet, croton, ixora, schefflera, copper plant and rubber tree, until new growth begins in the spring, and you can more accurately determine which parts are alive and what is dead," Gill said.
Dead leaves on woody tropical plants can be picked off to make things look neater. If you can clearly determine what branches are dead on a woody plant, you can prune them back.