Several key species of the hibiscus genus produce huge, dramatic flowers that are highly prized by gardeners. The tropical types that are planted outdoors in warmer climates are often used in containers in cooler climates, but there are also hardy perennial hibiscus varieties that are excellent outdoor perennial plants in most climates. But however, and wherever, hibiscus are grown, they offer some of the most spectacular flowers available.
The Hibiscus genus includes hundreds of species of annual and perennial plants with woody stems, grown both for their glossy deep-green or bronze-colored leaves, and for large flowers in a wide range of colors, including white, red, pink, orange, yellow, and peach. Some authorities divide hibiscus into three main types: tropical hibiscus, hardy perennial hibiscus, and hardy shrub hibiscus. However, only the tropical hibiscus and hardy perennial hibiscus are considered here. Hardy shrub hibiscus is more often known by its common name, rose of Sharon.
Tropical hibiscus (Hibiscus rosa-sinensis) plants are used as container specimens in cooler climates or as shrubs or small tree in tropical climates (USDA hardiness zones 9 to 11). The trumpet-shaped flowers are 3 to 8 inches in diameter with dramatic protruding stamens. Flowers are produced constantly, but each blossom lasts only one day. These plants can grow as high as 15 feet in good garden locations, but in colder climates are often planted as container specimens that are either replanted annually or brought indoors during the cold months.
Hardy perennial hibiscus (Hibiscus moscheutos) produces huge dinner-plate-sized blossom in shades of white, pink, and red, and is a herbaceous perennial in zones 4 to 11. It is sometimes called rose mallow or swamp mallow. It dies back to the ground each winter and resprouts in the spring. These plants grow from 2 to 7 feet in height.
Various hibiscus species are native throughout the world. Hundreds of species are included in the genus, but outdoor landscape use focuses on two species and their many varieties and cultivars: Hibiscus rosa-sinensis (often called Chinese hibiscus) and Hibiscus moscheutos (swamp mallow or rose mallow).
Hibisus rosa-sinensis is native to tropical regions of Asia. In USDA hardiness zones 9 to 11, it is an evergreen perennial, but can be planted as an annual or a container specimen in other climates.
Hibiscus moscheutos is native to wet landscapes from Ontario and Massachusetts south to Ohio, Indiana, Alabama and Florida. It is perennial in USDA hardiness zones 5 to 9, and several cultivars are highly prized landscape plants.
In warmer climates, tropical hibiscus is grown as a perennial garden plant and is used as a woody shrub for hedges and screens. In colder climates, it is often planted in large containers as a patio or deck specimen. Tropical hibiscus can grow as high as 12 or 15 feet, but when brought indoors, it is usually trimmed back to 5 or 6 feet.
Hardy perennial hibiscus works well in moist areas, as individual specimen plants, or in loosely define shrub islands or borders. Its fondness for moist areas makes it ideal for rain gardens.
Techniques for growing hibiscus depend on the type of plant, with tropical types requiring somewhat different care than the hardy perennial types.
While most plant tags will tell you that tropical hibiscus takes full sun to partial sun, in reality, if you live somewhere hot and bright, you should go more towards a partial sun location. In Northern climates, however, your hibiscus will probably be happier in full sun.
Tropical hibiscus is a thirsty plant and will only thrive and produce blossoms if it is given enough water. Depending on heat, wind, and humidity, your plant may need to be watered daily, or even twice a day in extremely dry conditions. However, soils need to be well drained. If your hibiscus is dropping leaves, or you're seeing yellowing leaves at the top of the hibiscus, chances are it's not getting enough water. If your hibiscus has yellowing leaves in the middle or towards the bottom of the plant, chances are it's suffocating from too much water.
For consistent flower production in container plantings, make sure to avoid very deep containers, which can cause the plant to spend its energy on root development at the expense of flowers. In mixed containers, the ideal pot shape is quite wide but relatively shallow.
When you buy a potted hibiscus, it likely has a slow release fertilizer mixed into the soil so it will not require much feeding in the first few months. After that, regular feeding with a diluted fish emulsion fertilizer will keep in blooming vigorously.
If you live in a northern climate, it is possible to overwinter hibiscus indoors, if you can provide 2 to 3 hours of daily direct sunlight. Your plant will need less water in the winter, but the dry indoor heat of winter is hard on tropical plants, so you will need frequent shallow waterings. If you see any buds, remove them—you don't want your hibiscus to flower in the winter. In the spring, cut the plant back and put it back outside once the nighttime temperatures are consistently above 50 F.
If your outdoor plant is consistently producing hibiscus flowers, it is happy, so keep doing what you're doing. If your plant is not producing buds and flowers, try moving it into an area that has either more or less sunlight.
Hardy Perennial Hibiscus
Hardy perennial hibiscus grows well in average soil with average-to-wet moisture levels. Moist soil with lots of organic material is ideal, but it will tolerate any average garden soil if it is kept moist. Plant it in full sun. It is immune to the heat and humidity of southern climates. The best flower production will occur in full-sun to light-shade locations where air circulation is good. Protect it from wind to reduce the chances of wind burn.
To make the plants bushier, pinch back the growth when the stems are about 8 inches long, and again when they are 12 inches. Deadhead spent flowers to maintain the plant's shape. Like most plants with large flowers, perennial hibiscus benefits from regular feeding during the active growth period.
In late fall, cut the stems back to within 3 to 4 inches of the ground. These plants are slow to return in the spring but grow very quickly once they do start.
- Hibiscus rosa-sinensis 'Bonjour': constantly blooms with red and pink flowers; grows 4 to 6 feet in height.
- Hibiscus sinensis 'Magic Moment' has 10-inch flowers in hues of peach, orange, pink, and light purple, on plants growing up to 8 feet tall.
Hardy perennial hibiscus:
- Hibiscus moscheutos 'Luna Red' is a compact 2 to 3-foot tall plant with 6 to 8-inch flowers in deep burgundy red.
Tropical hibiscus: Generally free of pests and diseases, but try to maintain consistent soil moisture and air temperature to help prevent yellow leaves.
Spider mites and aphids are common insect pests. Plants can develop bacterial diseases due to transmission from insects, rain, and fog; symptoms are leaf wilt, dwarfing, stem rot, and distortion of leaves.
Hardy perennial hibiscus: No serious insect or disease problems. Some susceptibility to leaf spots, blights, rusts, and canker.
Japanese beetles can severely damage foliage, but don't kill the plant. Whiteflies, aphids, and scale may be seen. Leaf scorch can occur if soils are allowed to dry out.