Extension Educator, Horticulture
As wild as a Hawaiian shirt, tropical plants bring an exciting look to gardens. Being tropical means these plants won't make it through our winters and many are damaged at temperatures below 55 degrees F. So do we let them die a cold death? Of course not! We are gardeners who hold on to each plant until the last cell succumbs. In addition many of the tropicals such as mandevilla and brugmansia actually flower better as the plant matures. Here are a few tips to keeping tropicals through the winter for continued beauty next season.
Mandevillas sometimes listed as dipladenia are dramatic vining plants with large glossy leaves and magnificent trumpet shaped flowers. Flowers are pink, red, purple or white. Mandevillas lend a tropical flair to landscapes as they twine around trellises, fences, lampposts, or mailboxes and are often grown in containers. Like many tropical vines mandevillas are fast growers putting on 7 to 10 feet per season. They can eventually reach 30 feet in the south or in a large greenhouse. Allamanda is similar to mandevilla but is more shrub-like.
The winter care of mandevillas like many tropicals can be one of two methods. If you have the space, they can be brought indoors and grown as a houseplant. Place the pot in a sunny location. A greenhouse is ideal. Water about once a week. Trim as needed to maintain the desired size. Mandevillas will not bloom through the winter due to the shorter days unless they receive supplemental lighting. With this method don't be alarmed if the mandevilla like many tropicals insist on going dormant and lose their leaves. They often look dreadful during the winter.
The other method is the "just don't die" method. Dig the mandevilla from the garden or bring in the container before temperatures get below 60 degrees F. Trim the plant back to about 8-10 inches. Wash plant thoroughly. Drench container soils with water to encourage any critters like ants and sowbugs to vacate. Store the plant in a cool dark basement, garage or crawlspace. Anywhere where the temperatures stay about 55-60 degrees is adequate. Do not fertilize during the winter.
Keep the soil on the dry side, but do not let it dry out completely. In the early spring the plant will form shoots. Move it to a sunny spot indoors and pinch shoots periodically to form a bushier, more floriferous vine. Before setting outside in late May or early June, repot and apply a water-soluble fertilizer. Do not set outside until all chances of frost have passed and temperatures stay above 60 degrees F.
Brugmansia or Angel's Trumpet with its monstrous fragrant fluted flowers is another popular tropical that can be treated in the winter much the same way as mandevilla.
Bananas are amazingly tough plants, but they are cold weather wimps. They grow a bit differently then most of our plants. Bananas are not true trees since they never form a woody stem. They are actually the largest herbaceous plant in the world. What appears to be a trunk is really the overlapping leaf bases or petioles of the giant leaves. They grow from a central crown so the leaves can be cut back and some of the side leaf petioles on the trunk can be removed so the plant is a manageable size to bring indoors. I kept one in the basement in a pot all winter with minimal light and water. It flourished the next summer. At the Idea Garden the bananas have been kept for 6 years and just get bigger and more beautiful. One even produced baby bananas this year.
Tropicals are worth the extra effort to nestle them in for a long winter's nap.