Tropical hibiscus (Hibiscus rosa-sinensis) is one of the most popular plants used in Louisiana and along the Gulf Coast. Summers in Louisiana are warm and humid, perfect conditions for growth of these tropical plants. With proper care, hibiscus can provide almost non-stop blooming from spring through the 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, tropi- cal hibiscus is not cold hardy. Protect from temperatures below 45 degrees F.
Soil and Bed Preparation
If planting tropical hibiscus in a land- scape bed, provide a soil pH between 6.5 to 6.8. This is a slightly acid soil. Soil pH can be increased by using dolomitic lime and decreased by using 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 the landscape bed area and after amending the area.
Tropical hibiscus needs a sunny loca- tion for optimum flowering and perfor- mance. Generally, 6 to 8 hours of full (direct) sun daily are optimum. The more
sun exposure your hibiscus receives, the more irrigation (supplemental watering) will be needed. 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 most of them are enjoyed in our landscapes. Many variet- ies 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 main- tain 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 yellow 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.
Magnesium sulfate, also called Epsom salt, gives hibiscus foliage a good dark green color. Add at the rate of one table- spoon per gallon of pot size to pots on a monthly schedule during the growing season. You can also spray magnesium sulfate on the foliage at the rate of one tablespoon per gallon of water. Epsom salt does not change the soil pH. It is considered pH neutral.
Several insects can be serious pests on hibiscus. These include thrips, aphids, spider mites, whiteflies and scale. After positive identification, treat with the recom- mended insecticide. Insecticidal soap and dormant/summer horticultural oil sprays also are recommended. Some damage to