How to care for Hibiscus

The queen of tropical flowers, the hibiscus is flamboyant and colourful and reminds us of far-flung warm climes when the temperature drops. Blooming in late summer and autumn, there are tender forms to enjoy in glasshouses, as well as hardier plants to grow outdoors.

There are 437 species of hibiscus – mostly native to the tropics and subtropics, in particular the coastal rim of the Indian and Pacific Oceans, where the large flowers bedeck temples and shrines. The most iconic of them all – Hibiscus rosa-sinensis – was introduced to Europe in 1731 and during the 18th and 19th centuries, its blooms became the symbol of all things exotic.

The genus encompasses a range of plant types, from low herbaceous perennials, to shrubs, and even large trees. A red tea is made from the garnet-coloured calyces of the subshrub Hibiscus sabdariffa (roselle) and drunk in many parts of the world, either hot or cold. It is rich in vitamin C and other nutrients and has a tart cranberry-like taste.

But the two hibiscuses that are of most interest to gardeners are H. syriacus and H. rosa-sinensis, both shrubs. H. syriacus is the hardiest and can be grown outdoors in the milder regions of the UK; its common names are rose of Sharon and Syrian hibiscus, but they are misnomers, since the plant hails from China, not the Israeli coast or Syria. In the right conditions, it is long lived and drought tolerant and produces wide pink, red, blue, or white flowers in late summer and autumn.

H. rosa-sinensis (the Chinese hibiscus) is a fabulous tender plant for a conservatory or greenhouse. It has been cultivated as an ornamental plant in China for thousands of years and is the most well-known hibiscus. The big letterbox-red flowers with long gold-tipped anthers are synonymous with Hawaii and Florida, where the plant has been used extensively as a parent to create some 10,000 hybrids, including yellow, peach, white, and pink forms. A collection of Chinese hibiscus hybrids was recently added to the large glasshouse at RHS Wisley, demonstrating how to grow them under cover. They are easy to grow in pots or in glasshouse beds, and – in good conditions – can flower for many months, injecting the much-needed colour and vim of the tropics on grey days.

Which hibiscuses to grow outdoors

The rose of Sharon (Hibiscus syriacus) is a great shrub in the milder half of the UK, having a good branching habit and forming a vase shape. In cold gardens, it can be planted in a pot and overwintered indoors. Arguably the most beautiful varieties are lavender blue – for instance 'Marina' and 'Oiseau Bleu'. But there are also lovely pink and white options, such as 'Woodbridge' and 'Red Heart'.

The swamp mallow (H. moscheutos) is a moisture-loving herbaceous perennial that can be grown outside in most parts of the country. Having large flowers (up to 30 centimetres wide), it can topple and therefore must be staked and isn't suitable for very windy gardens. 'Midnight Marvel' is a rich red cultivar.

H. trionum is a lovely rarely seen perennial that can be grown as an annual in very well-drained soil in sun. The primrose-cream flowers have maroon-black centres that give the plant some of its common names: black-eyed Susan, goodnight at noon, and devil's head in a bush.

Which hibiscus to grow in a greenhouse or conservatory

The legendary Chinese hibiscus (Hibiscus rosa-sinensis) and its hybrids are super plants for a heated greenhouse or conservatory. The flowers of the species are a bold shade of crimson and can be 25 centimetres wide; like daylilies, they last for one day, but the plant will produce a profusion of them. In Malaysia, these flowers were once used to dye hair and eyebrows and colour shoe polish; and, across Asia, different parts of the plant are still used in traditional medicine. There are umpteen hybrids available, in lush, vivid colours.

How to plant hibiscus

Both H. syriacus and H. rosa-sinensis can be grown in pots or in the ground. Because the roots are shallow and like to spread, a wide pot is best (ideally glazed clay, timber, or stone to maintain an even temperature) and, when grown in the ground, ensure the shrub isn't crowded by other plants. If necessary, add grit to soil to provide the aeration and drainage that hibiscuses crave; in a pot, use a mix of loam, compost, and sand. Water the plant well before planting. Don't plant deeply, ensuring the stem is the same level with the soil, as it was with the compost in its pot.

How to grow hibiscus

• Hardiness: H. syriacus is the only hibiscus shrub to try growing in the ground outside in the milder counties of the UK or on the coast or in cities. Ideally, give it a warm, sheltered south-facing wall. In cold regions, it is better in a pot that can be wheeled inside for winter; alternatively, wrap the plant in hessian or bracken.
• Light: H. syriacus and H. rosa-sinensis must have full sun outside, but in a conservatory or greenhouse in summer, semi-shade is fine.
• Soil: A very free-draining soil is essential, so add pebbles, gravel, pot pieces, or anything that creates it, before planting. Growing on a slope or bank is also great for drainage, as is a raised bed, with the latter having the added advantage of warming the roots somewhat.
• Moisture: Hibiscuses like a lot of moisture in the growing season. This should be provided by regular thorough soakings (rather than frequent light waterings), as well as mulching.
• Nutrients: Start feeding hibiscus in spring and continue until early autumn; this is especially important for container-grown plants. Use a liquid seaweed feed or any potassium-rich fertiliser; citrus food and rose food will also do. Hibiscus responds very well to mulching, and this can be done little and often throughout the growing season, using compost, well-rotted manure, pine needles, coconut fibre, or leafmould.
• Pruning: If necessary, a hibiscus shrub can be cut back by half in winter.

Hibiscus pests and diseases

Mealybugs, aphids, scale insects, and whitefly can be a problem on H. rosa-sinensis and H. syriacus, especially in a greenhouse. Regularly pick off insects by hand to reduce the problem. Both are also susceptible to powdery mildew, where air flow and moisture levels are poor. Slugs and snails are fond of H. moscheutos.