Bringing the Tropics Back Indoors

A tropical look on the deck is very “in,” but soon you’ll have to bring those plants in—indoors, that is!—to save them from the cold. Photo: Atlantic Gardening Company, www.trianglegardener.com

The tropical style has dominated our terraces and balconies for a few years now. Every spring, garden centers fill up with tropical-looking plants with huge leaves, exuberant growth and brilliantly showy flowers, plants that find easy takers and decorate our patios, balconies and terraces from the very first days of summer on. But that summer is coming to an end. These great and glorious plants will soon freeze and turn into mush if you do nothing. Should you save them? Can you save them? If so, how? 

Here’s a summary of the possibilities.

Banana (Musa spp. and Ensete spp.)

Nothing says “tropical” better than a banana tree (technically, bananas aren’t trees, but herbs) with its large paddle-shaped leaves, sometimes 5 feet (1.5 m) long. There are now many varieties on the market: big ones, small ones, with green, purple or variously marbled leaves. There is even a “hardy banana” (Musa basjoo) that will indeed survive the winter in mild climates (zone 8, sometimes 7 with protection), but is certainly not where I live (USDA zone 3)! Any banana you intend to keep in a cold-winter climate, you’ll need to bring indoors.

There are two ways to overwinter a banana tree indoors: in growth and dormant.

To keep your banana growing, bring it in early, while the nights are still warm. Place it in front of a sunny window and continue to water it all winter.

To learn how to bring any tropical plant indoors without also bringing in unwanted bugs, read Bring Your Plants Indoors Without the Bugs. 

But sometimes your favorite banana is just too big for your living room or maybe you don’t want to have to deal with watering it all winter. If so, you can force it into dormancy. Wait until the nights cool down to about 40 °F (5 °C) (this will slow its growth), then cut it back to a stump to between 4 and 6 inches (10-15 cm) high. That’s easy enough to do because the banana’s pseudotrunk isn’t woody and is just made up of interlocking leaf bases.

Place the pot in a barely heated room and stop watering completely. In spring, around March, expose the stump to greater heat and plenty of sunshine. Start watering it and soon your banana will be growing again.

Note that bananas are unlikely to ever produce bananas in a temperate climate, regardless of the care you give them. It’s better to consider them as plants grown for their ornamental foliage.

Brugmansia or Angel’s Trumpet (Brugmansia spp.)

This large shrub or small tree produces a lot of rather large leaves, but its main charm comes from its huge pendulous trumpet-shaped flowers, highly scented in the evening. Again, two treatments are available to those who want to bring it indoors for the winter.

You can keep the plant growing and even get decent bloom indoors until about Christmas. After that, natural sunlight is generally too weak, and the plant will remain a rather ordinary foliage plant for the rest of the winter. When brugmansias are growing, you have to give them the most intense sun you can, good atmospheric humidity (to keep spider mites at bay) and temperatures above 50 °F (10 °C).

You can also put your brugmansia into dormancy. Cut all branches back (you can root them as cuttings to make more plants if you want), leaving it with a trunk and a few rather short branches. Place the plant in a barely heated garage, a closet or a dark basement. No light is required. Water a little, about every three weeks, just enough so that the soil doesn’t dry up completely. The leaves, if any remain, will fall off on their own: compost them. In March, expose the plant to the sun again, then start watering and fertilizing to launch a new flowering season.

Canna (Canna spp.)

With its large green, purple or multicolored paddle-shaped leaves, a canna looks a lot like a banana plant, but it blooms much more readily. To keep it over the winter, let it undergo a touch of frost, enough to kill back the foliage. Cut the stems between 1 to 2 inches (2-5 cm) in height.

If yours is growing in a pot, just bring the pot into the house as is. If your canna is growing in the ground, dig it up and place its large rhizomes in a perforated box, covering them with sawdust, newspaper or peat. In both cases, keep the plant in a cool basement or in a barely heated garage. No light and no watering will be needed in the winter as the plant will be fully dormant. In the spring, repot it, start watering it again and expose it to full sun. Soon it will be up and growing again.

Hibiscus (Hibiscus rosa-sinensis)

Very popular on decks and balconies, but not the easiest plant to bring indoors. It can suffer a mightily during the transition back to indoor conditions, often losing most if its leaves.

To help acclimatize it without leaf loss, bring it in early (early September is not too soon!) and cover it with a large, clear bag to maintain high humidity. After two weeks in this “greenhouse,” start removing the bag gradually over another two-week period; this will allow the hibiscus to gradually adapt to the drier, dimmer conditions indoors and leaf loss will be minimal.

During the winter, your hibiscus will need as much sunshine as you can give it and abundant watering (never let it dry to the point of wilting). In early March, unless you want it to reach the size of a small car, cut it back seriously. This will stimulate abundant branching, followed by a summer flush of flowers.

Oleander (Nerium oleander)

Not quite tropical (you can leave it outdoors in zones 9 and 10), the oleander, a tall shrub or small tree, prefers cool temperatures during the winter, between 40 and 60 °F (5-15 °C). You can put it in a cool basement or in a barely heated garage, reducing watering to minimum. Even though this plant holds on to its leaves during the dormant period, it won’t be photosynthesizing to any degree if you’re not watering it and won’t need light. 

You can also grow it as a houseplant, offering it strong light and regular watering.

To keep oleanders under control, cut them back by one third when you bring them in for the winter.

Elephant’s Ear (Alocasia, Colocasia, Caladium)

There are several plants called elephant’s ear, all the Araceae family. Some have green foliage, others colorful foliage, but they always have large arrowhead-shaped leaves. Hidden underground is a tuber where they’ve stored energy for the coming season. That means you can cut back their foliage and put them into dormancy, storing them dry and cool like a canna (information above).

Majesty Palm (Ravenea rivularis)

This palm came out of nowhere a few years back to become the hit of the summer and you now see it everywhere: decks, balconies, restaurant terraces, municipal plantings, etc. With its large arching fronds, it creates a beautiful tropical effect, but then so would just about any palm. The difference is that it’s much cheaper than other palms, hence its popularity.

Indoors, though, the majesty palm is actually one of the harder palms to grow, often losing most of its fronds or out and out dying. To keep it happy, give it full sun and high humidity, perhaps using a humidifier. Keep watering it: it doesn’t appreciate dry soil. It’s very prone to spider mites (red spider mites) when the air is dry. Shower it regularly to control them if they show up.

Castor Bean (Ricinus communis)

In spite of its shrubby appearance, it’s best to treat this plant with thick, tall stems and huge palmate leaves as an annual: it just isn’t happy indoors, so let it freeze. Fortunately, the castor bean plant is easy to grow from seeds sown in May and its seeds are easy to find.

And Many Others…

The descriptions above only cover a few varieties, but the choice of tropical-looking plants for the terrace is huge. Think of begonias, mandevillas, papyrus, pennisetums, fatsias, etc. In general, they can all be brought indoors in the fall and treated like houseplants, so offer them good light, regular waterings and keep the atmospheric humidity up (no plant likes dry air!). No need to fertilize them from fall through winter but, as of March, start feeding them again with a simple all-purpose fertilizer. That’s all you need to keep them happy.

But do bring all tropical indoors fairly early in the fall: leaving them outdoors until nights start to grow cold can seriously harm their growth.