Richard Bogren, Huffstickler, Kyle, Gill, Daniel J., Owings, Allen D.
Louisiana has many great plants that thrive in summer and fall. Some are tropical-like in appearance. They include cassias, princess flowers (also called tibouchinas) and durantas. 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 alata (which we may know as candlestick tree) and Cassia corymbosa.
Cassia splendida is usually the tallest-growing – making a 10- to 12-foot-tall tree. Cassia corymbosa is most often a medium to large shrub, and the candlestick tree can vary greatly in size depending on age and location. It is common to see them 12-15 feet tall in the more southern portions of the state with a 6- to 8-foot height common in the Florida parishes. Candlestick trees have more herbaceous-type growth, and the other species have more woody-type growth.
All species have a tendency to need trimming and pruning occasionally to keep the plants in a manageable growth pattern. Although the best time to remove dead wood is right after new growth commences in the spring, you also can prune slightly during the growing season to manage growth. But don’t get carried away with pruning after early summer or you’ll sacrifice fall flowers.
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 (Tibouchina) include several species. One of the lesser known species is glory flower (T. grandifolia), 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 the 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 T. urvilleana. It is also called Athens Blue tibouchina or dwarf tibouchina. We have been growing it at the LSU AgCenter the past three years, and it is a great landscape performer with profuse blooms from late spring through fall on 18- to 24-inch-tall plants. A variegated-foliage form of this plant is now available.
Dewdrops is a common name for durantas, which also are called sky flowers. One dwarf variety is Cuban Gold. It is low-growing, reaching only 16-20 inches tall in the landscape by fall.
Durantas prefer full sun. Because chartreuse foliage color is its main characteristic, it can be a great substitute for chartreuse-foliaged ornamental sweet potatoes. It is recommended as a perennial in south Louisiana and is a great annual elsewhere.
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 Lemon Drop, Variegated, White, Purple and Silver Lining.
As we move into the heat of midsummer, try some cassias, tibouchinas or durantas if you can find them at your garden centers. You will be pleased with having some great plants that really will be showstoppers through fall.
Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.lsuagcenter.com/lahouse or www.lsuagcenter.com/lyn.