David Robson: Tending tropical plants in northern climates
For making a statement in the garden, nothing beats big tropical foliage plants.
While hardy only in areas that don’t get below 45 degrees, you can bring them indoors for the winter. Or you can treat them like annuals and let them freeze, but, for green-thumbers, that’s difficult.
Banana leaves, elephant ears and cannas make the most visual impact. Like all tropical plants, they thrive in the Midwest summer humidity and heat, and they dislike cool temperatures.
Cannas are practically Victorian in nature, with gardeners growing them for years, overwintering the rhizomes in boxes in the basement only to plant them again the following spring.
The typical canna has plain green leaves and red foliage, giving it almost a Christmas appearance in August. Occasionally, you will find plants with yellow flowers.
In the 1990s, the All-America Selections came out with Tropical Rose, a pink flowering form from seed. It made a brief effect, but it has since been relegated to specialty catalogs. It wasn’t bad; it’s just that newer introductions have more of a “Wow!” effect.
Like many tropicals, the foliage is becoming more important than the flowers. Besides rolling off the tongue, the Tropicana cannas are plants of choice.
Tropicana Gold cannas have variegated foliage of green with orange-red stripes that almost approach yellow as the plant gets more sun and the leaf ages. Leaves may end up approaching two feet long and 10 inches across as the plant matures. If it never produces the orange flowers, you still have a stunning garden specimen.
To satisfy fans of darker foliage, Tropicana Black has almost pure burgundy-black leaves as they unfurl, showing orange variegation as the leaves age. They also have orange flowers, which many gardeners remove. The downside to Tropicana cannas is they attract Japanese beetles.
Elephant ears is a catch-all term for two similar plants: colocasia and alocasia. Alocasia is stiffer with crimpled leaf margins while colocasia is floppier and less thick. Both grow from a large bulb that can be overwintered in the same box as cannas.
There seems to be a wider variety of colocasia on the market, with green leaves speckled with a dark red, such as Margarita. Some are cup-shaped with leaves looking like stingrays, hence the names Tea Cup and Stingray.
Black Magic and rhubarb are dark red leaf varieties, some with brilliant red petioles or leaf stems. Alocasia, sadly, tends toward the green, though some leaves have dark prominent veins of white, yellow or red. The shades of green vary from chartreuse to a dark forest hue. A couple have a contrasting shade on the underside.
Generally speaking, the alocasia are smaller than most colocasia, but the regular green alocasia can be larger than the smaller colocasia. So there’s no hard-and-fast rule.
Unlike the cannas, elephant ears don’t seem to attract Japanese beetles, but only a fool would state that as an absolute.
Finally, there are the bananas. Bananas will never be a perfectly clean garden plant. A little wind and the leaves tear, though some gardeners think that gives the plant character. Leaves come and go, but the plant keeps producing.
Unlike elephant ears, bananas can tolerate a little drought, but not as well as cannas. Also, don’t count on the plants bearing fruit. They might if you keep bringing them indoors or live where temperatures allow year-round sun tanning.
Bananas have gone the same route as the other three; what once started as green foliage plants have morphed into those with speckles and splotches of colors, as well as those leaves approaching a black red.
Cannas, elephant ears and bananas are perfect for container planting, as long as the container is large enough to allow for growth. All of these plants can tolerate lots of water as long as the soil is loose, loose and looser still.
Many gardeners will plant elephant ears and cannas in pots with holes, and then sink those pots in another container without holes, with water always in the outer pot. That’s fine, though the water can get stagnant and become a mosquito breeding ground.
All four could be planted directly in the ground, but make sure you don’t over water them. In-ground planting promotes more root and bulb rots as the soil isn’t as loose and aerated. Add lots of compost or composted manures, and you can improve the chances of success. Consider fertilizing once a month with a water-soluble fertilizer.
Give them as much sun and warmth as possible. Shade may be acceptable for some elephant ears, but you’ll find the best growth with sun from early morning until late afternoon.
David Robson is a specialist with the University of Illinois Extension. For more gardening information or for your local extension unit office, go to www.extension.uiuc.edu/mg.