Looking for tropical plants appropriate for Louisiana?
Big leaf tibouchina creates a show in a sunny landscape with purple flowers at the LSU AgCenter Hammond Research Station from late summer through fall. (Photo by Allen Owings)
By Allen Owings, LSU AgCenter horticulturist
HAMMOND – A research and extension program at the LSU AgCenter Hammond Research Station this year and next year – along with some work the past two years – is the evaluation of tropical and tropical-like landscape plants.
Funding for work with some of these tropicals with potential is being provided by the Lafayette-based Louisiana Society for Horticultural Research.
Louisiana has many great plants that thrive in summer and fall. Many woody and herbaceous tropical and similar plants do great this time of year. But the big question is which will over-winter and which will not?
Many times it may be best to consider treating these plants as annuals in the landscape and not be concerned with cold hardiness. In fact, considering how much beauty and enjoyment these plants provide, most are not more expensive than a premium annual plant.
We regularly think of bananas, gingers and tropical hibiscus in this category. But some of the tropical-looking plants we can really enjoy are not as highly used, including cassias, princess flowers (also called tibouchinas), duranta and copper plants. All are low-maintenance.
Cassias are among the popular plants that flower from late summer through fall and can be found at many retail garden centers. These plants are sometimes called sennas. They produce yellow flowers on prolific plants and are a landscape “showstopper” in September and October.
Several cassias are common in Louisiana. Probably the best that fits a mostly tree-like description is Cassia splendida. Other species are Cassia alatam, also known as the candlestick tree, and Cassia corymbosa.
Cassias are trouble-free and easy to grow. Plant them in full to partial sun and fertilize them regularly. Cassias need minimum irrigation once established. These are perennial in south Louisiana and can return in other areas of the state after a mild winter.
Princess flowers include several species. One of the lesser-known species is glory flower, also known as big leaf tibouchina. It has much larger foliage and larger flowers than the other commonly grown princess flowers. Considered a tropical or tender perennial, the plant is winter-hardy most years in USDA hardiness zone 9A, which is generally south of I-10/I-12. Purple flowers start in late summer and continue through fall. Plants can be easily rooted using softwood cuttings. A few garden centers in Louisiana sell this plant, which needs to be used more.
Another great species is Athens Blue tibouchina or dwarf tibouchina. We have been growing it at Hammond five years now, and it is a great landscape performer with profuse blooms from late spring through fall on 24- to 30-inch-tall plants. A new species of variegated-foliage princess flower from Asia is now available.
Dewdrops and sky flower are common names for durantas. One dwarf variety, Cuban Gold, is low-growing, reaching only 16-20 inches tall in the landscape by fall. The variety Gold Edge produces few if any seed pods or flowers and grows to a height of 5 feet each year. Other varieties available in Louisiana include Sapphire Showers, Lemon Drop, Variegated, White, Purple and Silver Lining. New varieties at Hammond are Green and Gold, Snow Flurry and Little Geisha Girl.
Some of the more unusual tropicals included in our current evaluations are pink-flowering, red-flowering and variegated-foliage jatropha, red orchid tree, bolo bolo plant, tropical lilac, variegated tropical hibiscus, several new varieties of yellow bells (yellow trumpet bush), bellyache bush, less cold-hardy buddleia, popcorn cassia, several less cold-hardy sages, a new bicolored tibouchina and much more.
You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website atwww.lsuagcenter.com/hammond. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.