Extension Educator, Horticulture
Lug it in? or Let it die? Each fall I am torn as to the fate of my tropical plants. Their very warm-blooded tropicalness renders them winter whimps. They pout at temperatures below 55 and may perish at temperatures below 40 degrees F.
Each year I tell myself I'm not going to drag all those plants into the house. But each year I can't stand to watch them succumb to a cold, cruel death. I refuse to surrender my plants to winter. If you too can not watch them die, here are a few tips to keep tropicals through the winter.
Tropicals that form a bulb, corm or rhizome are fairly easy to keep. These include elephant's ear, caladium, canna, dahlia, and gladiolus. Dig the bulbs, allow the soil and leaves to dry then store bulbs in peat moss or sawdust in boxes at temperatures between 40-50 degrees F.
The winter care of tropicals such as mandevilla, hibiscus, angel's trumpet (brugmansia) and bananas can be one of two methods: grow as a houseplant or store as a dormant plant.
Tropicals can be amiable houseplants but are often gentle giants requiring plenty of space. Dig the tropical from the garden or bring in the container ideally before day temperatures get below 60 degrees F and before frost. All is not lost if they experience a little frost nip. Trim plant to a manageable size. Wash plant thoroughly to remove as many insects as possible. Dug plants should be potted into well-drained potting soil. Place the pot in a sunny location or under fluorescent lights.
Water tropicals as houseplants about once a week. Do not fertilize during the winter. Periodically check for insects such as spider mites. Don't be alarmed if tropicals insist on going dormant and lose their leaves. Reduce watering if they go into dormancy. They often look dreadful during the winter, but they will recover once spring arrives.
The other method is known as "just don't die". Many plants have natural adaptations to survive in a dormant state while they wait for better growing conditions. To keep tropicals as dormant plants leave them in the original pot or place them in a plastic-lined cardboard box, milk crate style box or plastic bag. Let the leaves die back naturally and if soil is particularly wet, let them dry on newspaper before storing. Dry soil can be left on roots. Store pots or crates in a cool dark basement, garage or crawlspace. Any location where the temperatures stay about 40-50 degrees is ideal. At higher temperatures plants may need a little moisture half way through winter.
Bananas are amazingly tough tropical plants. They are not true trees since they never form a woody stem. What appears to be a trunk is really the overlapping leaf bases or petioles of the giant leaves. They grow from a central crown near the base 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. Even large ones are fairly easy to dig. I keep mine in the basement in a pot all winter with minimal light and water. Bananas can also be brought indoors to be stored dormant in a plastic bag in a cool dry place. For two springs dormant bananas have fooled me into thinking they were dead only to arise alive and well from my compost pile.
One banana species, Musa basjoo, is reportedly hardy to zone 4 if given at least 2 feet of mulch.