With one freeze behind us, adjust your plant-survival strategies (2024)

This winter continues to be unusually cold, unusually early.

View full sizeIllustration by Tony O. Champagne

On the south shore, where temperatures have barely dipped below the low 30s, damage to landscapes likely has been light.

North shore gardeners have seen killing freezes in the mid- to low 20s that have burned back or, if they were not protected, killed some tropicals. And the winter is just getting started.

It's time to assess the effects of these recent freezes and to evaluate how well your efforts to protect plants helped to minimize damage.

Don't be overly distressed if that tropical plant you carefully covered and tucked in for the night shows freeze damage anyway. Covering plants doesn't mean they'll come through freezes in perfect condition. It means they'll live to recover.

Only plants in pots, which can be moved into a greenhouse or a brightly lit location indoors, can be expected to go through the winter in excellent shape.

Here's how to handle your plants after a freeze.

Container plants

Unless you are keeping them inside for the rest of the winter, move container plants back to their outdoor spots outside once a freeze is over.

It does not bother these plants to go in and out again as needed through the winter. And, unless you have excellent growing conditions indoors or have a greenhouse, container plants would likely be happiest spending most of the winter outside.

If you placed your container plants together under a porch or covered patio and covered them with sheets or plastic, uncover them and decide whether you want to return them to their original locations or leave them where they are.

They can stay sheltered as long as you space them apart and make sure they get adequate light.

Plants in the ground

Plants growing in the ground must be sheltered in place by covering them.

For plants covered with clear plastic, you must remove or vent the covers to prevent excessive heat buildup if the next day is sunny and mild. You don't have to completely remove the cover if temperatures will be freezing again the next night.

In fact, you can leave plants covered with blankets or sheets for several days without harming them if freezes are likely for several nights in a row. But eventually the covers must be removed so the plants can get light.

The leaves of tropical plants will freeze where they touch a plastic cover (this happens less with fabric covers). For this reason, if you simply drape a plastic cover over a plant, it is typical for the outer leaves to look burned.

To minimize leaf burn, support the plastic cover up off of the foliage. A tomato cage works well for this, or simply drive three stakes that stick up slightly taller than the plant into the ground around it before you cover it.

Remember, covers usually protect plants from radiational freezes on chilly, clear nights or when temperatures stay in the mid-20s or above. Under these circ*mstances, heat radiates from the surfaces of plants and the soil into the environment, and covers prevent this.

For more severe freezes, minimize damage by providing heat under the cover. Draping the plant with small, incandescent outdoor Christmas lights before you cover it and leaving them on all night is a good way to do this.

Dealing with cold damage

The first thing that many gardeners want to do right after a freeze is to get out and start whacking everything back. Don't do it.

Wait a week or more after a freeze to prune. It often takes a week or two for all of the damage to become evident.

Damaged growth on herbaceous or nonwoody plants, such as cannas, elephant ears, birds-of-paradise, begonias, impatiens, philodendron and gingers, may be pruned 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.

Most of these plants have fleshy below-ground parts, such as bulbs or rhizomes, that will survive the winter and grow next year. A 4-inch layer of mulch over the ground is all that is needed to protect them.

You can remove the damaged foliage from banana trees, but do not cut back the trunks unless you can tell for sure that they have been killed (usually this takes temperatures in the teens). A dead trunk will look brown, feel mushy, feel loose in the soil and will bleed if punctured.

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 which are dead. Dead leaves on woody tropical plants can be picked off to make things look neater.

If you can clearly determine which branches are dead on a woody plant, go ahead and prune them back. Try scratching the bark with your thumbnail: If the tissue underneath is green, it's still alive; if the tissue is tan or brown, the branch is dead. Start at the top and work your way down to see how far back the plant was killed.

Don't get discouraged at this point. Although you may see a fair amount of damage to landscape tropicals, particularly on the north shore, most of the tropicals are still alive and will appreciate continuing protection as needed through the rest of the winter.

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DAN GILL'S MAILBOX

Last week you mentioned that different tropical plants have different degrees of hardiness. Do you have any printed information that shows at what temperatures different tropicals could be damaged?

Jason Harrison

Yes, I have a good listing of commonly used tropical plants that shows the temperatures that will likely damage or kill them. Send me an e-mail request to dgill@agcenter.lsu.edu and I'll be happy to send you a copy. This information also discusses various techniques for cold protection.

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I know you have answered this question a thousand times. The leaves on my azaleas are turning yellow. Do I worry? If so, what can I do?

Miguel Soler

This time of the year, yellow leaves (or orange or red, depending on the variety) on azaleas are generally just the older leaves being shed from the plant. This is a natural occurrence, and there is no cause for alarm. Depending on how many leaves the shrubs drop (it varies from year to year and plant to plant), they may look a little skimpy. But, they will fill back in when the new growth emerges in spring.

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Are there any trees that would provide the color changes in our area that we see in the Blue Ridge Mountains? I would love to have a couple in my yard.

Sandra Bonnet

We will never have the fall color down here that happens up north. But, as long as your expectations are not too high, we do have trees that will color fairly well. Some years will be better than others, depending on the weather. Among the maples, I'd recommend our native Drummond (or swamp) red maple, Autumn Glory maple and Florida Flame maple (these are all types of red maple, Acer rubrum). The Japanese maples (Acer palmatum) color well most years (I particularly like the Coral Bark Japanese maple) and the Florida maple (or Southern sugar maple, Acer saccharum var. floridanum) also colors in shades of gold and orange. Other trees to consider reliable for fall color in the Deep South are ginkgo (Ginkgo biloba), crape myrtle (Lagerstroemia), flowering pears (Pyrus calleryana) like Bradford, Cleveland Select and Capitol, sweetgum (Liquidambar styraciflua), Shumard oak (Quercus shumardii) and Chinese pistachio (Pistachia chinensis). The Chinese tallow tree (Triadica sebifera) is very reliable about providing fall color, but I recommend you avoid this invasive nonnative.

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I planted several Camelot foxgloves near the end of October, and they are blooming right now. I thought they wouldn't bloom until the spring. If I continue to cut the stems back after the blossoms have fallen off, will they continue to bloom through the spring? Will the cold weather affect them?

Nancy Davis

If plants were large enough and planted early, we are finding they are blooming this fall. Some nurseries are even selling large, blooming plants. Plants blooming this fall will likely stop blooming over the coldest part of winter and produce another great (likely even better) display of flowers in spring. Do cut off the faded flower spikes. This will keep the plants vigorous and encourage more flowering. They are very hardy.

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Dan Gill is extension horticulturist with the LSU Ag Center.

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Dan Gill, garden columnist

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