By Dan Gill
LSU AgCenter Horticulturist
As cold winter weather begins to settle in over the state this month, we can expect freezing temperatures in the 20s and even occasionally the teens for the next few months. With cold weather comes concern for tropical plants in our landscapes.
When we use the terms "tropical" or "tropical plants," we are referring to plants native to parts of the world where temperatures are warm year-round and freezing temperatures do not occur. As a result, plant species native to these climates have evolved little ability to withstand subfreezing temperatures. Because we live in a mild-temperate climate where winter temperatures can go well below freezing, these tropical plants are subject to injury or death during our winters.
What is it, then, that makes us want to grow tropicals? Perhaps it is that our winters may be mild-temperate, but our summers are definitely hot, humid and rainy like much of the tropics. It is very satisfying to watch tropical plants flourish in our hot, rainy summer weather, providing bold foliage and color. Another reason for the popularity of tropical plants is their incredible beauty. They often have large leaves that create a lush look in the landscape. Many tropicals are grown for their exotic flowers and have extended bloom periods that stretch through the summer. They keep on flowering no matter how hot it gets. And tropicals produce some of our most fragrant garden flowers.
Hardy versus tender
Hardy and tender are gardening terms that refer to how much cold a plant can tolerate. Hardy indicates plants that will reliably survive winter temperatures where you garden with little or no protection.
The term tender applies to plants that would not reliably survive the cold of a typical winter where you garden. Many tropicals are tender. We use these plants as well in our landscapes. Although a series of mild winters may lull you into thinking these plants are hardy in your landscape, a winter is sure to eventually come along to show you otherwise. Tender tropical plants should not form the backbone of your landscape. Place them strategically in the landscape to provide bold, tropical accents.
A huge selection of hardy trees, shrubs, lawns, perennials and ground covers native to climates like ours are available to us. These hardy plants are not bothered by winter cold. In addition, a good number of tropical plants have enough hardiness to reliably survive winters in Louisiana, especially in the southern part of the state. But north Louisiana gardeners grow tropicals, too.
In most cases, hardy plants and hardier tropicals should form the backbone and majority of your landscape planting. Otherwise you run the risk of losing and having to replant a substantial part of your landscape every few years.
If you expect tender plants to survive hard to severe winter freezes, you have to be willing to protect them as needed through the winter – and this can add considerably to landscape maintenance. Because of their beauty and reliable summer performance, however, we are often willing to protect them over the winter or replace them when theyíre lost to cold.
Protection includes deep mulching to protect the base of the plant. If the top freezes, the lower parts protected by the mulch may survive and resprout. Protection also may be provided by covering the entire plant with plastic sheets, tarps, cardboard boxes, fabric sheets and other materials.
If protection is too much trouble, you may just decide to allow the tender tropicals to die and replace them in the spring. I like to plant a mandevilla vine on a trellis. The plant costs about $15 and grows and blooms beautifully all summer. When winter freezes come, I donít protect it. I grow it as an annual and only expect to get one season. Iím perfectly happy to spend another $15 in spring to purchase a new plant and save myself the bother of protecting a plant all winter. So, here are the points to consider when using tropicals in your landscape:
• All tropicals are not equally hardy or tender.
• Some tropicals are killed by temperatures in the upper 20s while others can survive temperatures in the upper teens (particularly those that have underground bulbs, rhizomes or tubers).
• Research or inquire at the nursery about the hardiness of any tropicals you consider planting in your landscape. Choose hardier tropicals when possible.
• Limit the use of tender tropicals in your landscape to some degree to prevent major devastation to your landscape when we experience severe freezes. Remember, use tropicals to embellish rather than as a major component.
• And finally, be most leery about planting tropicals that will grow to be large plants or trees. If a series of mild winters allows them to grow large, they may be impossible to protect. Then when freezes kill them, they leave major gaps in the landscape and can be expensive to remove.