Hibiscus or rose mallow (Hibiscus rosa-sinensis) is a staple of tropical and subtropical gardens that is so common that its incredible flowers are often taken for granted. The plant is originally from South Asia but is now ubiquitous around the world and can even be grown as an indoor pot plant in cold climates. There are thousands of cultivars with single- and double-petaled flowers coming in white, yellow, orange, pink and red. Hibiscus plants can grow up to 10 feet high with scentless flowers up to 6 inches across. While the flowers only last for one day, they are produced in abundance throughout the year.
Hibiscus plants thrive in deep, rich soil that is free draining and slightly acidic but will grow well almost anywhere provided that the soil is not waterlogged. In gardens with heavy clay soils, hibiscuss should be planted in raised beds to maximize drainage. Plant your hibiscus in a sheltered spot with full sun or high shade for the best growth and flower production. When planting, bury deep enough to cover the root ball but do not cover the main stem. For hedges, allow about 3 feet between plants.
Water your hibiscus plant when the surface of the soil is dry but do not allow the root ball to dry out. Twice a week during the growing season should be enough. If your plant has a lot of yellow leaves on it during the summer it is likely to be under-watered. During the winter, hibiscus plants need less water but the soil should be kept damp. Indoor potted hibiscus plants are vulnerable to both drying out and water-logging. Do not keep the pot on a saucer and water every other day if the plant is in a sunny spot.
During the spring when hibiscus plants are producing a lot of new foliage they need high-nitrogen liquid fertilizer at half strength every two weeks. As flower production increases during the summer a micro-nutrient enriched liquid fertilizer at half strength every two weeks is ideal, decreasing to once a month during the autumn and winter. Over-fertilizing with full-strength fertilizer can burn the roots of hibiscus plants, especially during hot weather, and can cause massive leaf drop.
Hibiscus plants can be pruned back heavily during the early spring and trimmed at any time of year. Heavy pruning stimulates flower production and stops large plants from becoming leggy. For hedges, plants should have their main growing tips pinched out as soon as they reach the desired height. The plants can then be pruned every year and will form a very neat hedge within only a couple of years. Hibiscus bushes also make excellent topiary subjects.
While generally hardy, hibiscus plants are vulnerable to attack from scale insects, aphids and mealybugs, as well as red spider mites. Insect pests should be treated with a systemic insecticide that enters the sap of the plant and poisons the pests when they feed. Red spider mites can be treated with a miticide but often simply soaking the leaves of the plant every morning and evening for a week will bring an infestation under control.
Hibiscus rosa-sinensis does not set seed and is best propagated via 6-inch tender shoot cuttings taken during the summer months. These should be dipped in commercial rooting powder and planted in damp compost inside a high-humidity propagator. Placing a transparent plastic bag over the pot will also maintain humidity. Cuttings take best at a uniform temperature of between 70 and 80 degrees Fahrenheit. Hibiscus can also be propagated via hardwood cuttings about a foot long and as thick as a pencil, planted in well-gritted compost and kept in humid, shady conditions.