March 2014 Articles

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Tropical hibiscuses add to spring, summer landscapes

Tropical hibiscuses add to spring, summer landscapes Source: Allen Owings, LSU AgCenter horticulturist
HAMMOND, La. – In Louisiana, we are ideally located to grow many plants that are adapted to more tropical and semi-tropical climates. This is especially true south of Interstate 10 and Interstate 12.
Even for those of us who cannot use tropical plants as perennials, many plants are still available to select from for colorful foliage and tropical flowers. One of the best plants for tropical flowers from midspring through fall is the tropical hibiscus.
Tropical hibiscuses go by the scientific name of Hibiscus rosa-sinensis. Our growing conditions are perfect for these plants. With proper care, hibiscuses can provide almost non-stop blooming from spring through fall. They can be used in landscape beds or as container-grown plants. Few plants will surpass tropical hibiscus for size, color and flower beauty. As its name suggests, tropical hibiscus is not cold hardy and must be protected from temperatures below 45 degrees.
If planting tropical hibiscus in a landscape bed, provide a soil pH between 6.5 and 6.8. This is slightly acidic. Soil pH can be increased by adding dolomitic lime and decreased by adding elemental sulfur or aluminum sulfate.
As with most ornamental plants, make sure the soil is well-drained. Most native soils in Louisiana are clay-type and typically poorly drained. Amend clay-based soils with sand and organic matter – pine bark, peat moss, etc. Always conduct a soil test before amending a landscape bed area and again after amending it.
Tropical hibiscus needs a sunny location for optimum flowering and performance. Generally, six to eight hours of full, direct sun daily are optimum. The more sun exposure your hibiscus receives, the more supplemental watering it will need. If plants start getting very large by late summer, afternoon shading may slow the watering requirement.
Container culture is ideal for tropical hibiscus. In fact, this is how we enjoy most of them in our landscapes. Many varieties may also bloom better if somewhat rootbound. Be sure to provide enough water and fertilizer. Containers can be placed on a patio, around the swimming pool, along the driveway or in a landscape bed. As winter approaches, bring plants indoors or maintain in a protected area to enjoy next year.
The biggest problem you’ll face when growing hibiscus, especially in containers, is drying out. Flower bud drop, sudden foliage decline and excessive yellowing of leaves are signs of excessive drying of the soil or container medium. Hibiscus in pots will need lots of water during the hottest days of summer. It’s also a good idea to use a water-soluble fertilizer in combination with irrigation.
Tropical hibiscus needs potassium fertilizer. This is important, in addition to a regular source of nitrogen. Use two to three times more potassium than nitrogen. A good fertilizer ratio for hibiscus is 12-4-18 or a “high bloom,” water-soluble fertilizer. Slow-release granular fertilizers, like Osmocote, can be used in combination with water-soluble fertilizer when irrigating.
Several insects can be serious pests on hibiscus. These include thrips, aphids, spider mites, whiteflies and scale. After positive identification, treat with the recommended insecticide. Insecticidal soap and dormant/summer horticultural oil sprays also are recommended.
It is great that in our state we have Louisiana-developed tropical hibiscuses from which to choose. The Cajun series hibiscus was developed by Bobby Dupont of Dupont Nursery in Plaquemine. These have some of the largest flowers of any of the tropical hibiscus, and the uniqueness of flower colors is impressive. The TradeWinds series tropical hibiscuses are also gaining in popularity and are being sold at retail garden centers. Colors in this series are numerous.