Tropical Plants to Overwinter
Tropical plants are native to warm, humid, frost-free zones but can provide interest to Pennsylvania gardens during the summer months and even beyond. Tropical plants can be large, imposing specimens. Offering exotic foliage or stunning flowers, tropicals can provide impact or complement other plants within containers as well as in a perennial or mixed border. Some can even create a privacy barrier, growing to fill a space in just one season. By learning to overwinter your tropical plants, you can keep your favorites, add to your collection over time, begin next season with bigger specimens, and save money in the process.
Fall is the time to decide which ones to save. Based on the type of plant, you have choices as to how and where to keep them alive during the winter months.
If you have space and the right indoor conditions, you may consider treating some tropicals as houseplants. Palm trees, banana, and even elephant ears can enhance your interior décor, but require abundant space, a bright sunny window, and added humidity. You can supplement natural light with fluorescent lamps. You can raise the humidity through misting, placing a tray of water and pebbles nearby, or grouping plants together. They must be brought inside before the first frost. Many tropicals will start struggling when nighttime temperatures drop into the low 40s, so plan ahead. Inspect them for insects and mites and treat if necessary. It is advisable to acclimate them to their indoor home over a period of time. For further information on bringing plants indoors, please review Bringing Houseplants Indoors.
Palm trees, cordyline (Cordyline fruticosa), New Zealand flax (Phormium tenax), Chinese hibiscus (Hibiscus rosa-sinensis), bird of paradise (Strelitzia reginae), mandevilla vine (Mandevilla sanderi), and angel's trumpet (Brugmansia) are tropical plants that must be overwintered as houseplants. Cut back the hibiscus, mandevilla, and angel's trumpet when you bring them inside. Less than ideal indoor conditions may cause some leaves to yellow and drop.
Some plants, such as coleus (Coleus scutellarioides), annual flowering geranium (Pelargonium x hybridum), and scented geranium (Pelargonium), are easily carried from one year to the next by propagating through rooting stem cuttings. Cut a six-inch healthy tip from the plant. Remove any lower leaves, dip the stem end in a rooting hormone and push into a container prepared with moistened potting mix. Water and cover with a clear plastic bag. Place in a warm location. After three to four weeks, the plant will have formed roots. Remove the plastic bag and place in a bright, sunny location. Keep it watered through the winter. You may need to trim it as it grows to keep it bushy.
Many plants with tuberous roots, whether they are technically corms, tubers, bulbs, or rhizomes, can be sent into dormancy and stored through the winter in a very cool but frost-free location, such as an attached garage or unheated basement. Ideal storage temperature for most is between 45°F and 55°F, with elephant ears preferring warmer temperatures into the 70°F range. This category includes canna (Canna), elephant ear (Colocasia, Alocasia, and Xanthosoma), dahlia (Dahlia), gladiolus (Gladiolus), caladium (Caladium x hortulanum), and banana (Musa). If they are container-grown, you can cut them back, leaving a few inches of the above-ground stem, and store the entire container in that cool, dark space. Check the plant periodically throughout the winter, and water only when completely dry. Too much water can lead to root rot. The ideal time for digging up the bulbs is after a light frost when the tops have died back but before a hard freeze when the roots could die. In my suburban southern Allegheny County garden, I have a tough bed of cannas that have overwintered outdoors in the same protected south-facing location for more than 15 years. Elsewhere in my garden, they do not survive. Elephant ears can survive a light frost, but not a hard freeze. Their bulbous roots will turn into mush. I choose to prepare them before the first frost. Cut off all but four to six inches of foliage and lay them in a warm place to dry for a few days. Add the foliage to your compost bin. You can leave some soil around the bulbous roots. Washing them will cause rot. To survive the winter, they must remain dry enough not to rot, but moist enough not to desiccate. Label them and place in a box with ventilation, barely covered with dry peat moss or potting soil. I have had success with storing the bulbs in plastic bins with the lid on but not sealed. Store in a cool, dark place. Check the bulbs during the winter and spray with a little water if they are starting to shrivel too much. Discard any that are rotting.
If you want to get a jump on the season, in the spring, about four to six weeks before the last frost in your area (about the same time you are starting tomatoes from seed), remove the tubers and pot them up in containers with a nutrient-rich well-draining soilless potting mix. Place these and any containers of tropical plants that you may have stored in a warm, sunny indoor spot. You may need to supplement with grow lights. I will often start them in a temporary home to transplant outdoors later. Clean, large, plastic nursery pots will serve this purpose. As with seedlings, you will need to acclimate these tropical plants to the harsh conditions of the outdoors. They can remain outdoors after nighttime temperatures remain above 50°F, like tomatoes and peppers.
You can also plant your overwintered tropicals directly into their summer location in your garden. Within no time at all, they will emerge from their winter dormancy and begin to fill your garden with a touch of the exotic.
