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Great Gardening: Storing tropical plants in winter

Most fine gardeners eventually discover the power of tropical plants. Mostly you’ll see these plants in containers, many of them huge. We use them for drama, and for bold colors. Among the most popular tropical plants are elephant ears, bananas, cannas, angel trumpets and caladiums. In recent decades dahlias – loved by connoisseurs since the 1800s – have seen a resurgence as Buffalo gardeners have added them en masse to their late July garden walk displays. Tropicals are in.

Then comes winter.

Many of these plants are classified as USDA Hardiness Zones 8 to 11, and they cannot tolerate freezing. Most grow from bulbs, corms or tubers – underground storage cellars for nutrients. These tropical tubers will survive the winter only if you dig them up and store them in the right conditions. Then you can replant them in spring, year after year. Don’t worry, however, if you were busy in early October and the first frost catches your cannas and caladiums still standing tall. It’s actually good for them to be touched by frost, as it turns leaves brown and signals the tuberous roots to initiate dormancy. Just get them out of the ground before a deep freeze.

The trick is figuring out how to handle these plants when they become enormous, and to find the right storage conditions.

What dahlia people do

Jim Locke and Annabelle Irey are the Garden Walk Buffalo gardeners on Lancaster Avenue who show a massive dahlia collection along with hundreds of other plants. “This year we will be over-wintering 155 dahlias. Our system is to dig the tubers when the plant shows signs of stress or fatigue. We cut off the stalks to within 6 inches of the ground and remove as much as soil as possible by hand from the tubers,” Jim said. (He said that “Flower Fairy” Annabelle is very popular during certain weeks as she gives away the flowers.)

The next step is critical for keeping tubers or bulbs healthy. “We dry the tubers in our garage/potting shed for a few days up to a week. We then put them in fruit baskets (with labels attached) in our cellar. We usually get about a 90 percent return rate,” Jim said. They use a similar method for elephant ears, cannas and pineapple lilies.

Opinions differ about washing or not washing bulbs and tubers when you lift them. Notice that Jim just brushes off the soil before drying them, whereas some experts wash the soil off. Either way, you must air dry them before they go into storage (typically packed in peat moss, sawdust, shredded paper, or fine bark mulch). Once they are stored, check every few weeks for rotting or drying and immediately discard rotting bulbs. Re-potting them begins in spring. Since they multiplied last summer, you will now have many more (and need more pots) than the year before.

Re-creating a tropical winter temperature is often the biggest challenge in cold climates. Our houses, including many basements, are too hot, and unattached garages or barns are too cold. The tubers survive best in dark places with temperatures between 40 and 50 degrees – just above freezing. That describes a typical cold cellar, but few homes still have them. The best spot might be some part of an attached but unheated porch or garage. Start moving a thermometer around now to see where to stack the bulbs in just a couple of weeks.

Large banana plants

Some years back some “hardy bananas” were trendy, and indeed some gardeners managed to over-winter them outside under a mountain of mulch or straw. The plants lived, but they took so long to grow a few feet tall that it was hardly worth the effort. My friends Gordon Ballard and Brian Olinski grow many tropicals and have tried every possible way to store a giant banana plant. One method: Cut it back to 8 inches above the crown and then store it in a cool place. But Gordon said: “Then we had to restart the plant in spring – and it’s not so successful if you want large lush banana trees.” The other methods: “Last year we grew them all winter in our basement with bright indirect plant lights. They do attract white flies so spraying was necessary. The absolute best way to store them: Find someone who has a big enough heated greenhouse and ask them to baby-sit your plants for the winter. Butter them up with seeds and plant divisions from your garden to say thanks,” he said. (Smart approach– but where are those greenhouse people?)

A mutual friend from Hamburg also told us how she un-pots the bananas to the bare roots, peels off all of the outer leaves to the core of the plant, rolls them up (in fabric or newspaper) and lays them flat on her basement floor until about February when she restarts them. So far it’s working.

Angels and elephants

Angel trumpets and tropical hibiscus plants might possibly flower for several months in your house if you have really bright lighting. Some people also keep elephant ears – Alocasia or Colocasia – growing successfully inside. (Colocasias can even stand in water.) Usually it works better to move all these plants inside before a frost, let them dry out and drop their leaves, and then store them in that 40- to 50-degree place. “I do keep about 18 pots of elephant ears over winter in my basement. Some are now 9 years old, with 8-inch diameter trunks. All but one leaf is cut off each plant. I give very little water over the winter – only a quart or so in the huge pots, much less in the smaller pots in January,” said Eden gardener Marcia Sully, another host to busloads of gardeners every summer.

Marcia is also known for an extreme over-wintering technique: She drives hundreds of bare-rooted tropical plants, annuals and succulents to Florida for the winter. There the tropicals grow in comfort, while the succulents laze about in the sand. Good plan for all!

This week look at your own tropical treasures and decide: Which will you save?

Sally Cunningham is a garden writer, lecturer and consultant.

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