Tropical Plants Love The Heat

Daniel Gill, Merrill, Thomas A.  |  6/29/2005 2:19:33 AM

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Get It Growing News For 07/22/05

By Dan Gill
LSU AgCenter Horticulturist

Plants that are native to tropical areas of the world are not bothered in the least by the hot days, muggy nights and frequent afternoon rain showers that we see during mid- to late summer in Louisiana. Indeed, that’s just the kind of weather they love.

For that reason, mid-summer is an excellent time to add tropical plants to the landscape. And tropical plants generally are readily available at area nurseries through the summer.

We grow tropical plants for a variety of reasons. Some, such as hibiscus, ixora, canna, angel trumpet, bird of paradise and butterfly ginger, are grown for their beautiful, and often fragrant, flowers. Others, such as peacock ginger, caladium, elephant ear and purple passion plant, are grown for their attractive, colorful foliage.

But no matter what tropicals you grow, it just seems they are an important part of summer gardens in Louisiana.

Gingers certainly are among the favorites of many gardeners. There are many different gingers that can fill a variety of gardening needs. Low-growing gingers, like Kaempferia pulchra, smaller species of Curcuma or Globba, make great ground covers or clumps at the front of shady borders. Medium-sized gingers, which grow 3 feet to 6 feet tall, include species and cultivars of Curcuma, Hedychium and Costus, while the shell ginger (Alpinia zerumbet) grows 10-12 feet tall. These larger gingers are excellent choices for accent, screens or at the back of a border.

Gardeners who are working with shady areas will find a gold mine of shade-tolerant plants among the gingers. In their natural habitats, most gingers grow under the canopies of trees in filtered light, although some grow in the open at the edge of water and in sunnier conditions. Most gingers will do best where they receive direct sun for about two hours to four hours a day and should not be planted in hot, sunny, dry locations. Shell ginger and some types of Curcuma and Costus will, however, grow in full sun. A thick mulch in winter will keep them coming back despite cold weather.

No other summer-flowering shrub surpasses the tropical hibiscus for glossy, dark green foliage and nonstop flowers in shades of and blends of pink, yellow, orange, white, lavender or scarlet. And the blooming season is very long, running from late spring through early winter in Louisiana. This plant often will survive winter in South Louisiana but is less reliable in the northern part of the state.

The tropical hibiscus, Hibiscus rosa-sinensis, thrives in sunny locations and looks great in beds or containers. The dwarf hibiscus plants you see offered are standard hibiscus plants that have been treated with plant growth regulators. Eventually the treatment will wear off (It generally lasts about one growing season.), and the plants will begin to grow to be their normal size.

Another group of tropical plants I really like are the clerodendrums. There are a number of species we grow in this state for their beautiful flowers and, in some cases, ornamental fruit. Perhaps the most well known is the cashmere bouquet (Clerodendrum bungei). Effortlessly easy to grow in part shade to shade, cashmere bouquet produces 4-5-foot-tall stalks with large clusters of small, fragrant, mauve flowers.

But it spreads rapidly. Many of the clerodendrums produce stems that run underground and produce plants some distance from the original plant, but none are quite as bad as cashmere bouquet. If you are aware of this habit and promptly remove sprouts from areas where you don’t want them, this is not a problem. But if you are the type of gardener who is not inclined to keep a careful eye out and remove them as necessary, cashmere bouquet can become a big pain – or let’s just say you probably shouldn’t plant it.

Another great Clerodendrum is the harlequin glory bower (Clerodendrum trichotomum). This large shrub to small tree looks as tropical as the rest, but it is, in fact, quite hardy. It drops its leaves in the winter but does not freeze back, even in North Louisiana. In July, large clusters of very fragrant white flowers last until August. Then amazing turquoise fruit continue the display.

As a group, clerodendrums are very attractive to butterflies and hummingbirds. One is even called butterfly shrub (Clerodendrum ugandense) because of the exquisite blue, butterfly-shaped flowers it produces.

Winter temperatures are an issue that needs to be thought about when using tropical plants in the landscape. Many tropicals will return very reliably from their roots or below-ground parts and make permanent additions to the landscape. Others are not so hardy and are more likely to succumb to the cold and should be used only where a permanent planting is not needed.

You also should be aware that tropicals generally are dormant in the winter, so don’t make them so dominant in your landscape that it is mostly bare during the cooler months.

If you read national gardening magazines regularly and get a variety of gardening catalogs, you may have noticed that "tropical look landscaping" is a trend that is gaining attention across the country these days. To Louisiana gardeners this "hot concept" is old hat. We’ve been gardening in the tropical style as long as anyone can remember.

But there is almost always room to try one more, and there are lots of great tropicals you can purchase and plant in your garden now.

Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.

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Contact: Dan Gill at (225) 578-2222 or dgill@agcenter.lsu.edu
Editor: Tom Merrill at (225) 578-2263 or tmerrill@agcenter.lsu.edu

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