Greenhouse Grower: Don't Bet The Farm On Tropicals

I have been evaluating new plants for a long time, and although I work with the plants themselves, I also get involved with the mindset of the people who are growing, selling and buying these new things. How easily can a new plant or a new idea (or an old one, for that matter), enter the mainstream of our industry? One of the trends I hear people discussing is the movement to tropical plants, and I am not even sure what plants they are talking about.

The tropics, by definition, is the area between the tropics of Cancer and Capricorn, which covers almost a quarter of the earth's surface and includes nearly one-third of the world's 250,000-plus known plant species. Therefore, nearly all our annuals, from alyssum to zinnia, can be defined as tropicals. Our most accepted foliage plants like coleus are tropicals, as are other mainstream flowering plants such as gerberas, cannas and daylilies. Yet when people are talking about tropical plants, they are not discussing these. So what are "tropical" plants? Perhaps it is like Supreme Court Justice Potter Stewart's definition of pornography: "I can't define it, but I know it when I see it."

The increased interest in "tropicals" for the grower, landscaper and user has to do more with a particular look than where it comes from. The plants I see bandied about as tropicals are diverse for sure, but the main ones belong to the ginger family, the banana family or the jack-in-the-pulpit family.

My Bet On Gingers

I see lots of interest in gingers. More than 1,300 species belong to this group, so it is not surprising that a few have been trying to mainstream. The two I see the most interest in around the country are the variegated shell ginger, alpinia and the peacock ginger, kaempferia. The former grows about 4 feet tall while the latter is only about 8 inches tall. Both produce flowers but are grown more for the foliage than for the blossoms. There are dozens of other gingers, including curcuma and globba, that are sometimes mentioned, but only the first two will likely ever see the light of day in mainstream horticulture. Even then, many producers are not interested in growing anything that requires additional heat, and these do. We are a rather conservative lot, and growing something that requires additional inputs with unknown value is not something we do readily. My money is still on kaempferia, a genus that is easily available as liners, grows well in shade, can be grown in 6-inch or gallon containers and, best of all, is sought after by landscapers.

My Bet On Bananas

The banana definitely provides a tropical look, but the banana phenomenon goes up and down like Mr. Otis. People get on the banana bandwagon for awhile, then they cool down. Between the genera musa and ensete, there are bananas for everyone. However, will bananas ever play in Peoria? One or two just might, and for my money, I think Musa basjoo might gain sufficient converts, as it is reliably hardy to Zone 5, and may be just the tropical look people are searching for. They can be moved out in 6-inch pots, but a 3-gallon container is needed to get some size on it. While these are still the bailiwick of botanical gardens and public spaces, somebody has to grow them.

My Bet On Jacks

Most of the movement to tropicals today can be traced to plants belonging to the jack-in-the-pulpit family (araceae), a large group of about 2,900 species. These include perennials like our native jack-in-the-pulpit, as well as houseplants from the tropics like dieffenbachia and philodendron. However, as far as plants for the tropical look outdoors, only a couple are poised for the mainstream. They are the ubiquitous taro, belonging to the genera alocasia and colocasia. I see these in containers from Minneapolis to Miami, in private gardens and public displays from coast to coast. At least a dozen cultivars are easily available through tissue culture, and their greenhouse and garden culture is simple. All are best displayed in large containers, but can be started in the greenhouse in gallon pots. My money is on these.

The Gambler

If I were a gambling man, and the bet was on what "tropicals" will be around in five years, I would first make sure it is not a trick question (i.e. petunias), then I would place my bets on the plants mentioned here. Many so-called tropicals are being produced, but let's get serious. They are limited because they require too much heat to produce and without sufficient heat, they are too slow. And in truth, from globba to siphonochilus, they are a little too weird for conservative gardeners and landscapers. That is not to say that such plants don't have their place, but probably not across the country.

Last, I am a believer in tropicals, just ask how many people ever thought a sweet potato would go public! But my comments here are the result of my talking and listening to people like you, from all around the country. I have little doubt that many tropicals that will never be mainstream nationally will be very important regionally. So, we will continue to evaluate tropicals in our trials, just don't ask me to bet on too many of them.

Allan Armitage

Contributing Editor

allan@greenhousegrower.com

About the author: Allan Armitage is a professor, Department of Horticulture, University of Georgia, Athens, Ga. You can e-mail him at allan@greenhouse grower.com.