Daniel Gill, Merrill, Thomas A. | 4/19/2005 10:28:53 PM
Get It Growing News For 6/18/04
No other summer-flowering shrub surpasses the tropical hibiscus (Hibiscus rosa-sinensis) for glossy, dark-green foliage and nonstop flowers in shades and blends of pink, yellow, orange, white, lavender or scarlet. And their exceptionally long blooming season runs from late spring through late fall.
Tropical hibiscuses can be planted in the ground or in containers. When planting in the ground, prepare the beds by digging in a generous amount (a 2-inch to 3-inch layer) of compost, peat moss or manure and a light application of a general-purpose fertilizer.
Plant hibiscuses in the ground any time during the summer. To do so, slightly untangle tightly packed root balls to encourage roots to spread into surrounding soil, and set the plants at the same level they were growing in the container.
Since tropical hibiscus plants are not reliably hardy in Louisiana, those planted in the ground are subject to injury or loss when winter temperatures go below the mid-20s. Keep this in mind when deciding how many and where to use these plants in the landscape.
On the other hand, hibiscuses make outstanding container plants, and you can bring them in on nights when freezing temperatures occur. For keeping them in containers, when you bring a new plant home, check the root ball. If it is very pot-bound, shift it into a container about one-third larger than the one in which it is growing. Otherwise, wait until later to repot, since hibiscuses tend to flower better if not allowed too much root room.
During the summer, fertilize your plants occasionally to keep them growing and blooming vigorously. Fertilize hibiscus plants growing in the ground using a granular, soluble or slow-release fertilizer according to label directions. Those in containers should be fertilized with your favorite soluble or slow-release fertilizer formulation.
Hibiscuses prefer an even supply of water and should not be allowed to wilt. Those in containers are especially vulnerable to drying out and may need daily watering in the summer. Water hibiscus plants growing in the ground regularly and thoroughly during hot, dry weather.
Providing enough light is especially important for abundant flower production. Hibiscuses should be given as much direct sunlight as possible – at least four hours to six hours a day, but eight hours of sun is preferred.
Pruning may be done anytime you feel the need to control or shape the bushes. How far back you cut depends on what you trying to accomplish.
When you prune, flower production will stop until the plant has made sufficient new growth. Generally, the farther back you cut your plant, the longer it will take to come back into flower. So it’s better to prune back lightly and occasionally than to allow the plant to grow too large and to have to prune more severely.
Yellow leaves often occur and are alarming but may not necessarily signal trouble. It is perfectly natural and healthy for a vigorously growing hibiscus to occasionally yellow and drop its older leaves. Leaves also may yellow and drop because of sudden changes in environmental conditions, and they may occur in a newly purchased hibiscus or a plant moved from one location to another.
On the other hand, yellowing leaves also may indicate a problem. A plant that is allowed to wilt may recover when watered but then drop leaves some time later. An overall pale, yellowish look to the plant indicates a need to fertilize. Yellow leaves also may mean the plant is infested with sucking insects – generally aphids or whiteflies. Look carefully for these pests, and, if observed, use a pesticide labeled to control them. Several applications may be necessary.
Flower bud loss is most likely due to stress from such factors as high temperatures, dry soil, low light, sudden environmental changes and transplanting. Some varieties of hibiscus seem to be more prone to bud drop than others.
Sometimes a healthy hibiscus will grow well but not produce flowers. As usual, several factors may be responsible. This will occur when newly purchased plants are repotted into a larger container or planted in the ground. This also will occur when plants are cut back severely. Under good growing conditions, the plants will eventually come into flower.
Insufficient light is another cause of poor flowering. Remember to give your plants as much direct sun as possible. Short days and low temperatures also reduce flower production.
Dwarf hibiscuses pack all the punch of larger plants in a much smaller package. They are ideal for window boxes, containers and flower beds.
Provide dwarf hibiscuses the same care as standard hibiscus, and enjoy the large colorful flowers produced on compact plants.
There is, however, a catch. Dwarf hibiscus plants are not smaller growing by nature – that is, they are not genetically dwarf. Instead, these are standard-size 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 at their normal rate. At that time, move them to a location where a larger plant would be appropriate.
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.