By Dan Gill
LSU AgCenter Horticulturist

The majority of plants in our landscapes are completely winter hardy. The primary concern during freezes is our tender plants in the ground or in outdoor containers. These plants – native to tropical regions of the world where it never freezes – do not have the ability to protect themselves from sub-freezing temperatures. If we want them to survive freezing temperatures during winter, we must provide protection for them.

First, identify the tender plants in your landscape that will need protection. The term tender refers to plants that are severely damaged or killed during typical winter temperatures. Plants such as hibiscus, tibouchina, firebush, angel trumpet, banana, gingers, palms, ixora, philodendron, pentas and oleander are just a few common plants that are subject to freeze injury at various temperatures.

You also need to decide what to do with your tender plants growing in outdoor containers. Basically, you have three choices:

– One, leave them out and take your chances during a freeze. If you do this, at least take down hanging baskets and gather your container plants together under some protection such as a carport, patio cover or large tree.

– Two, bring them inside and keep them indoors until spring. Make sure you put them in front of windows that receive plenty of light.

– Three, move them inside on those nights when a freeze is predicted and back out again when the freezing episode is over.

It is likely you will place some of your container plants into each category. Leave outside low-value, easily replaced plants or those too big to bring in. Move those that are easily transported in and out as needed during winter. Bring larger, more valuable plants inside to stay. These steps should be taken any time temperatures are predicted to go into the low 30s or upper 20s.

Plants growing in the ground cannot be moved indoors and must be protected in place. Remember, you do not necessarily need to protect everything that is tender. For plants growing in the ground that are readily available in nurseries and not too expensive to replace, you could just replant in spring if you lose them. I put plants such as pentas, lantana, Mexican heather, begonias, impatiens, blue daze and coleus in this category.

A benefit of our relatively mild winters is that temperatures don’t stay cold long enough to freeze the ground. Tropicals growing in the ground that produce fleshy underground parts, such as bulbs or rhizomes, are generally very reliable about coming back even if the tops are frozen back. Cannas, agapanthus, gingers, callas, elephant ears, achimenes, philodendrons, birds-of-paradise, crinums, hymenocallis and amaryllis fall into this category.

You can ensure the survival of below-ground parts or the crown of a plant by placing 4-6 inches of mulch, such as pine straw, over the soil around the base to provide additional protection. Should any of these plants suffer cold injury to their tops this winter, cut them back as needed.

Mulches only protect what they cover. Mulch may help keep the lower stems, crown and roots alive, but they won’t protect the uncovered upper parts of the plant. To protect the upper part of tropical plants growing in the ground, you must cover them.

Plastic, canvas or fabric all make suitable covers. To properly protect a plant, you must use enough material to extend all the way to the ground when the plant is covered. The goal is to trap the heat stored in the earth under the cover. If possible, find two or three posts or stakes that are taller than the plant, and drive them into the ground around the plant so they will keep the cover from touching the foliage. This is particularly important if the weight of the cover might damage the plant or if you use plastic because leaves will freeze where they come into contact with it. Secure the bottom edges of the cover with rocks, bricks or soil to keep cold air from blowing in. Remove or vent covers during the day if the weather is sunny and mild.

For severe freezes or prolonged temperatures below freezing, providing a heat source under the cover improves protection. One of the safest and easiest methods I’ve come across is to wrap or drape the plant with strings of small outdoor Christmas lights. They don’t generate enough heat to damage the plant, but what heat is given off by the small bulbs can make a big difference in a plant’s survival. Make sure you use outdoor extension cords.

Wetting plant foliage immediately prior to a freeze does not provide any protection, but it is important that plants are not drought stressed going into a freeze. If the weather has been dry, thoroughly water plants in the ground and in containers early in the day when a freeze is predicted for that night.

Tropical plants can be used effectively in the landscape, but they must be protected or replaced when necessary. Generally, the best idea is to plant mostly hardy plants and use tropicals with restraint so that your landscape is not totally devastated in the event an extremely cold episode occurs.