By Dan Gill
LSU AgCenter Horticulturist
(01/06/17) Although winter temperatures in Louisiana are generally relatively mild, they are punctuated by periods of moderate to severe freezes. Freezing weather is often followed by extended periods when temperatures stay above freezing.
Prior to a major freeze, most gardeners will make an effort to protect tender tropical plants in their landscape. So what should be done for the landscape after a freezing episode is over? Here’s some general information on what to do and not do.
Plants in pots
Any container plants that were brought inside for protection may be moved back to their location outside unless you intend to keep them inside all winter. If you will keep them inside, make sure they are close to windows and receive plenty of light. You cannot keep plants inside dark garages or storage sheds for extended periods of time. Plants must have light to create the food they need to live, and they will slowly starve if not provided enough light.
Many gardeners use a variety of covers to protect plants from freezing temperatures. Remove or vent clear plastic covers on plants to prevent excessive heat buildup if the next day is sunny and mild. The plastic will let in light and trap the heat, just like your car with the windows rolled up. You do not need to completely remove the cover if a freeze is expected again the next night. Plants covered with blankets, tarps, opaque plastic or fabric sheets may be left covered for several days without harming them, but eventually the cover will need to be removed so they can get light.
Pruning damaged plants
Even though you may see damage immediately, do not prune anything for a few days to a week after a freeze. It often takes several days for all damage to be apparent.
Damaged growth on herbaceous or non-woody plants, such as cannas, elephant ears, agapanthus, amaryllis, birds-of-paradise, begonias, impatiens, philodendron and gingers, may be pruned back to living tissue. This pruning is optional but does help keep the winter garden looking neat. Damaged tissue that is oozy, mushy, slimy and foul smelling should be removed. This decaying tissue is unhealthy for the plant.
Remove the damaged foliage from banana trees, but do not cut back the trunk unless you are sure it has been killed. It will look brown, feel mushy, be loose in the soil and bleed if punctured. If it’s alive, allowing the trunk to remain increases the chances of fruit production next summer.
Dead leaves on woody tropical plants, such as hibiscus, croton, ixora, cassia, bougainvillea and copper plant, can be picked off to make things look neater. If you can clearly determine which branches are dead, you may 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.
This pruning is optional and will not help the plant deal with the damage. Generally, it’s a better idea to delay hard pruning of woody plants until new growth begins in the spring. Then you can more accurately determine which parts have survived the winter and what is dead. Living parts will send out new growth.
Another group of plants that are generally severely damaged or killed by freezes are tender perennial bedding plants such as impatiens, wax begonias, pentas, blue daze, scaevola, periwinkle and coleus. Although it’s nice when they make it through mild winters and provide another year of flowers in our landscape, we must remember these plants are not intended to be permanent.
If, or when, plants have been killed by sub-freezing temperatures, remove the dead plants from the bed and mulch the area to keep it looking neat. You could also prepare the bed and plant hardy cool-season bedding plants, such as pansies, dianthus, alyssum, snapdragons or many others, anytime now through early March for an outstanding display this spring.
Remember, there is still plenty of time to see additional – and possibly more severe – freezes before it’s all over. Protect what you can when needed. Don’t be too quick to dig up and remove tropical plants that have been severely damaged and appear to be dead. Sometimes, they may eventually resprout from the base of the plant or the roots in April or May. Despite what comes, remember that our climate encourages rapid growth and recovery.
If worse comes to worse and you do lose some of the tender plants and tropicals in your garden, don’t think of it as a tragedy but as an opportunity. How many of us have filled every square inch of planting space in our gardens, reducing our chances to purchase and plant new types of plants we want to try? When the dead plants are removed, we will have open areas available. Think about that, and the loss might not seem so bad.
Green tissue under the bark indicates the plant is still alive. Photo by Dan Gill
Damaged herbaceous tissue that gets mushy and leaks liquid should be removed. Photo by Dan Gill
Herbaceous plants - like gingers - can be cut back a few days after a killing freeze. Photo by Dan Gill