Hibiscus: Tropical Gems of the Garden
Hawaiian State Flower
This high phosphorus fertilizer applied in late Spring on fully mature shrubs will insure continuous blooms through the summer months.
Close your eyes for a moment and try to visualize the look of a lovely South Pacific Island girl. The beautiful large bloom in her long flowing black hair is probably a hibiscus. It is the most recognizable and beloved of the tropical flowers, and, though exotic in appearance, is easy to grow.
Hibiscus is in the mallow family and is a distant cousin of the hollyhock. It comes to us from Asia and the islands of the Pacfic Ocean. One variety, Hibiscus brackenridgei, is the state flower of Hawaii. Another, Hibiscus rosa-sinensis, comes from China, and its brilliant red variety serves as the national flower of Malaysia.
There are hundreds of hybrids with blooms ranging from 3" to 12" across. Hibiscus moscheutos is a 6-8 ft. shrub (hardy hibiscus) that produces the largest flowers. Some blooms reach up to a foot across! In recent years the tropical "Hotbiscus" was introduced. It is grafted onto a mother root to insure the plant's ability to thrive in different climate zones. This class of hybrids features an amazing array of color combinations in spectacular patterns on oversized blooms. They are indeed eye-catching!
Hibiscus is definitely a tropical plant which ideally prefers a temperature range of 60-90 degrees. California, Florida, and Hawaii provide the best climates for year-round growth in the U.S.; however, these exotic beauties can be enjoyed elsewhere with a few more considerations.
In temperate areas, hibiscus can reach 15 feet in the garden making it a good choice for a showy hedge. Fast growing, these can gain 3 feet in just one year! Some more compact varieties such as the showy "hotbiscus" will stay under 3 ft. where they are perfectly suited for containers. These plants are very cold sensitive. As winter approaches, it is important to heed frost warnings and cover plants with plastic sheeting or a cloth for the night. Mulching will help to protect roots from the cold as well. Strong wind can also damage these tropical gems..
In regions with winter temperatures consistently below freezing, it is preferable to grow hibiscus in pots which can easily be brought indoors. Plants will need to be pruned to within 5" of the main stem and will most likely drop all leaves until they are placed outdoors again in spring. It is essential to provide 6-8 hours of bright light indoors even if it has to come from fluorescent sources. Although some growers will enjoy continuous indoor blooms in the cool season with ample light and fertilizers, it is important to give your plant a rest and not force blooming at this time. When placed outside in late March, the hibiscus will begin to leaf out and prepare for warm season flowering by June. Treating hibiscus as an annual in the coldest climates is also a good to way to insure a stunning display of prolific blooms.
General care: Hibiscus needs at least 6-8 hours of sun per day. The exception is Hotbiscus which can take quite a bit of shade. In hot inland areas, plants will need midday shelter from the hottest sun. Red varieties are usually more heat-tolerant. All hibiscus needs regular deep-watering during the blooming period and should never be allowed to completely dry out. This is especially important during the first 2 years of growth. Extreme fluctuations in watering will make the plant more prone to insect damage. Since these plants are heavy feeders, it is important to fertilize every 4-6 weeks during the growing season. As tempting as it may be to give them a super bloomer, they still need ample potash. Choose one that has both phosphorus and significant potassium like Gro-more Hawaiian Bud & Bloom. An organic food like a 6-5-3 is also a good choice, especially on newer shrubs. A feeding with iron and micro-nutrients in the spring will help with the yellow leaves and support overall vigor. Dead-head spent flowers and lightly prune to shape. This will encourage more blooms.
Biological controls for whitefly make the most sense for heavy infestations.
Parasitic wasps are an effective control for white flies without the use of toxic sprays and systemic poisons.
Pests and Diseases: Hibiscus is generally not prone to disease. Overwatering in the dormant season can cause root-rot, but it is rare. Also, it is important to NEVER let a container plant sit in a saucer of water. A plant will drown without aeration to its roots. Avoiding a soggy environment will also dissuade fungus gnats which lay eggs on wet potting soil.
Young buds are magnets for aphid infestation and occasional thrips damage. Aphids are very visible and can be easily washed off with a good blast of water or fed to hungry ladybugs and lacewing larva. Thrips on the other hand are so tiny that plant damage is the first indication of their presence. Unopened buds, deformed leaves, yellowing, and bud drop are symptoms. (High summer temperatures also cause buds to drop before opening.) To confirm your suspicion of thrips, tap a bud or flower over a clean sheet of white paper, and you should be able to see them scurrying way. A magnifyer is helpful.
Spider mites are tiny reddish spiders which weave delicate webs over branch ends. Prevention is best. Consistent watering and occasional plant washing to rid the leaves of dust and air-born pollutants will help. Use an organic control like insecticidal soap or neem oil once mites show up. Be sure to check undersides of leaves.
White flies are a common pest and difficult to get rid of once the plant is heavily infested. The adults lay eggs on the undersides of leaves and cover them with a waxy coating to protect them. A member of the lady beetle family, delphastus pusillus, is a native to Florida and works to keep common white flies under control. They can be ordered as home garden controls at www.tiptopbio.com. The Giant Whitefly- aleurodicus dugesii- comes from Mexico and is a real problem here in California and elsewhere. The long spiral waxy filaments look like white hair and are a shock to gardeners! There are two different schools of thought re. pest control: 1. use a strong control at the onset of the problem and 2. start with the mildest remedy first and go for heavier artillery as needed.
I recommend the second approach even though it requires more diligence and patience. Eradicating bugs without true necessity often skews the balance in the food chain and creates an even bigger problem. The USDA also uses a parasitic wasp- Encarsia formosa- as a biological control against the whitefly. Some insecticides might kill beneficial insects too. If chemical controls are used, a systemic, rather than a topical one, is best. These are applied as a soil drench and are taken up through the root system. The plant will then kill or repel would-be feeders. Again, prevention is the best approach:
1) Keep the plants healthy with proper care.
2) Apply worm castings at the time of planting. (refer to link)
3) Routinely clean tops and undersides of leaves with a blast of water.
4) Apply neem or paraffinic oil spray as needed.
If the problem still continues, a systemic pesticide that works from the inside out may be called for.
Ants are usually present with whiteflies and aphids because they harvest the sticky honeydew that the insects produce. The sticky deposits on the leaves blacken with mold and interfere with the plant's ability to perform photosynthesis, further weakening the plant. Use organic controls like Tanglefoot goo applied to strips of paper and wrapped around tree branches. Diatomaceous Earth, the crushed skeletons of tiny sea creatures, pierces the ant bodies and dries them up. It can be applied to ant nests or sprinkled around the edges of containers.
Worm castings have a built-in insect repellent and are rich in minerals.
- Worm Castings: A Gardener's Secret to Success
Raising worms, called vermiculture, is gaining in popularity today due to the common practice of backyard composting. Worms are decomposers and speed up the breakdown of the organic matter in the compost pile...
Worm castings provide natural insect resistance and add essential minerals and nutrients for vigorous growth.
As soon as the danger of frost is gone and the sun lingers longer, it will be the perfect time to plant some of these tropical gems. Whether planting in containers or in the ground, apply a bit or micorrhizae fertilizer next to the rootball to help the roots take up nutrients. Water, fertilize regularly, place in a nice sunny area until the summer heat becomes intense, and keep an eye out for insects. By the first of July, you will have a spectacular show of blooms to enjoy all summer long. Put on your aloha shirt and grab that Mai Tai. Ah! paradise!
© 2011 Catherine Tally
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