How to Grow Hibiscus
Hibiscus are part of the mallow family and according to Dr. William C. Welch, mallows have "the largest flowers of any hardy perennial." For sheer impact, you can't beat hardy hibiscus, H. moscheutos in the landscape. H. mutabilis is hardy to Zone 7b and is seen throughout southern states which explains its common name, Confederate rose. When speaking of hibiscus, H. syriacus, commonly known as rose-of-sharon, isn't often considered part of the hibiscus family, but it is. There's also tropical hibiscus, H. rosa-sinensis, that is only hardy to Zone 9, but is such a pretty accent wherever its grown. Then, there's Texas star hibiscus, H. coccineus which has unique, palmate leaves often confused with marijuana. Several newer varieties of H. acetosella, red-leaf hibiscus like 'Haight Ashbury' and 'Maple Sugar' are grown almost entirely for their leaf shape and color.
So, with all of these choices, how do you care for each type of hibiscus?
H. rosa-sinensis, tropical hibiscus, and H. acetosella, red-leaf hibiscus, are usually hardy from USDA Zone 9 to 11. Tropical hibiscus are known by their dark, glossy leaves and single or double flowers in bright shades of red, pink, yellow or orange. H. acetosella are grown mostly for their leaf shape and color which remind some gardeners of Japanese maples. Their flowers are considered insignificant. Grow both in well-drained, slightly acidic soil with a pH between 6.5 to 6.8 that retains moisture. Tropical hibiscus need consistent moisture while actively growing. Tropical and red-leaf hibiscus are frost tender. They prefer temperatures from 60 and 90F. If temperatures go below 50F, tropical hibiscus will quit blooming. Temperatures over 95F or other plant stress will cause blossom drop. In the hottest parts of the country, all hibiscus benefit from a little shade during the hottest part of the day. However, they need 6 to 8 hours of sunlight to bloom their best.
Use an all-purpose fertilizer with micro- nutrients for best results. Avoid fertilizers high in phosphorous. Try organic fertilizers made from worm castings, manure or compost. During the growing season, water soluble fertilizers like manure teas, are ideal.
Tropical hibiscus can be grown in ground or in containers. In areas with harder winters, containers are ideal because these can be moved indoors in fall. Tropical hibiscus can be overwintered indoors in a sunny window if desired. Only water in winter when soil is dry as plants don't need as much moisture.
Tropical hibiscus are susceptible to aphids, thrips, spider mites, scale and whiteflies. A hard spray of water will drown many of these pests. Turn over leaves to reach the little beasties. If you must spray a pesticide, use insecticidal soap for aphids, or better yet, encourage ladybugs to make your garden their home by planting other flowers rich in nectar for adults. For other natural pesticides, read the label before applying.
H. moscheutos, hardy hibiscus, rose mallow or swamp rose mallow, is extremely easy to grow with consistent water and full sun, and it's hardy to USDA Zone 5. Hardy hibiscus die back to the ground in winter, but re-emerge as soon as late spring temperatures become consistently warm. They can be slow to emerge so don't panic. Hardy hibiscus grow best in well-drained, consistently moist soils rich in organic matter. However, they also perform in leaner soils with less water than some hibiscus. Provide them with good organic fertilizer, and you'll be rewarded with fantastic growth and blooms starting mid-summer and continuing into fall. Pests include Japanese beetles, sawflies and grasshoppers. Use Nolo Bait as a natural defense for grasshoppers. Various organic pesticides will work for other insects, but read directions before using. Because hibiscus are such great pollinator plants, systemic insecticides can harm bees and other pollinators that visit so don't use systemic pesticides.
H. coccineus, Texas hardy hibiscus, scarlet rosemallow, swamp hibiscus and crimson rosemallow, is native to Texas and much of the deep south. It is often found near swamps and other boggy conditions. It requires consistent water and can be grown in full sun or partial shade. Rosemallow makes a great plant for rain gardens. 'Alba' is a white selection. 'Texas Star' is a crimson variety and is attractive to hummingbirds. All types are visited by butterflies.
- Hibiscus are large and dramatic. Their flowers usually only last one day.
- Blooms and plants can be very large depending upon variety.
- Large leaves of some varieties attract Japanese beetles and grasshoppers.
- Blossom drop on tropical varieties is a sure sign of distress. Check soil moisture and ambient outdoor temperature.
- All varieties are very easy to grow and provide great flowers or foliage for the landscape.
- Hibiscus are excellent pollinator plants too being attractive to bees, hummingbirds and other pollinators. Think before using systemic insecticides which are harmful to nectaring insects.