With a few exceptions, most tropical plants need a frost-free environment to successfully overwinter and be used as perennial plants in the garden. Geographically, this leaves most areas of the United States unsuitable for growing tropical plants as perennials. However, that doesn't mean gardeners across the United States can't enjoy tropical plants during the growing season as annuals. In regions where the heat of the growing season is followed by frost or freezing temperatures, tropical plants are often dug up and overwintered, used as houseplants, or simply repurchased for use the next growing season.
When using tropical plants as annuals, it is still important to remember that tropical plants do well in heat but not in cold.
"It pays to be especially cautious with some plants," says Mary Kroening, University of Missouri Extension specialist. "We're getting so many wonderful tropical plants through the nurseries. Plants like Coleus, Mandevilla, Lantana, Hibiscus, and Acalypha really don't do well with temperatures below 45 degrees, and if it gets below 40 the plant starts to shut down, and may not recover. Another popular climbing plant for hanging baskets is Thunbergia (black-eyed Susan vine). Forty is really pushing it. Tropical plants really thrive in the hot summers, thus planting when too cool can be detrimental. However, the advantage of tropical plants is they are spectacular in the heat of summer when other plants start to suffer."
In areas where it is not uncommon for growing-season temperatures to dip into the 40s or where summer temperatures do not generate enough heat for tropical plant growth, it may be a struggle to get tropical plants to perform well. In areas with these growing conditions, gardeners may want to turn to using tropical look-a-likes - plants that do not require as much heat for growth but still have big, bold, or colorful tropical-looking foliage.
Will you grow tropical plants as annuals or perennials? Selection and culture of plants will vary depending on your answer to this question. The following resources provide information on using tropical plants in the garden.
For those gardening in hardiness zones 9 and 10, you can learn more about tropical plants by watching:
-"Tropical Plants 8/8/07" covers plants to use for tropical gardens in the south.
-"Growing Tropicals 5/10/06" covers how to select plants and locations for growing tropical plants as perennials.