Hibiscus care: light, water and more blooms

Light

Sources pull in slightly different directions here. NC State lists full sun to partial shade and says an indoor plant needs a spot with bright light, and Clemson grows it outdoors in full sun or light afternoon shade. The RHS, writing for a cloudier climate and for plants behind glass, asks for bright, filtered light protected from direct sun in a greenhouse, yet says a south-facing windowsill will do in winter. In practice, indoors in the US that means the brightest window you have, which on the Illinois Extension scale is high light of 300 foot-candles or more, with a sheer curtain only if leaves bleach in midsummer afternoon sun.

Light is what drives flowering. A hibiscus in a dim room grows soft, leafy shoots and few buds. Outdoors for the summer, it usually blooms far more, but Clemson advises acclimating it gradually to the stronger light, and bringing it in again needs the same care in reverse.

Water

NC State says the roots should be kept moist, and Clemson tells growers to water the plants freely during the growing season. A flowering hibiscus with dozens of large leaves in a warm, bright window uses a lot of water, and a pot allowed to dry out completely tends to shed its buds. Check the surface often in summer and water as soon as it feels dry, soaking until water runs out of the drainage hole.

The RHS frames watering around the seasons. In spring, increase watering as rising light and temperatures stimulate growth. As growth slows in fall, reduce it, and in winter water only when the top layer of compost is dry. In cool conditions the plant overwinters semi-dormant, and that rest is healthy rather than a sign of trouble.

Do not let the pot stand in water at any time of year. Moist roots and waterlogged roots are different things; a saucer full of water in winter, when the plant is barely using any, is an invitation to root rot.

Soil and pH

NC State and Clemson both ask for rich soil with good drainage, Clemson specifying plenty of organic matter. For pots, the RHS recommends a peat-free compost formulated for houseplants, or a soil-based compost such as John Innes No 2. A quality bagged houseplant mix with some compost or loam added holds moisture between waterings while still draining freely. Any container must have a drainage hole, and a heavier pot helps once the plant reaches 3 feet or more.

Humidity

NC State notes that Chinese hibiscus appreciates high humidity, and the RHS describes it as needing bright, humid conditions with good ventilation. A heated home in winter often drops below 30 percent humidity, according to the Illinois Extension, which partly explains the winter leaf and bud drop. The RHS raises humidity by standing the pot on a tray of damp gravel or clay pellets and grouping plants together. Dry air also favors red spider mites, one of the main hibiscus pests.

Temperature

The RHS gives a minimum night temperature of 45°F (7°C) and calls 45 to 50°F (7 to 10°C) nights ideal for overwintering in a greenhouse; an ordinary home is warmer than that, which is fine. More useful is the outdoor cutoff. The RHS says to bring plants in before temperatures drop below 54°F (12°C), and Clemson says to move tropical hibiscus indoors when nighttime temperatures fall into the lower 50s °F. UF/IFAS warns that the slightest cold wave can make lower leaves yellow and drop. Indoors, keep it away from open fires, radiators and drafts, and pull it back from windows on frosty nights.

Fertilizer

Tropical hibiscus is a heavy feeder while it grows. The RHS recommends starting weekly feeding with a balanced liquid houseplant fertilizer about six to eight weeks after the late-winter repotting and continuing through spring and summer. That is far more often than the general Illinois Extension rule for foliage houseplants, and it reflects how much energy a plant spends producing a new flower almost every day. Follow the label rate. When growth slows in fall, cease feeding, as the RHS advises, and resume only when spring growth starts.

Work out the dose for your watering can with the fertilizer dilution calculator →

Repotting

The RHS repots tropical hibiscus in February or early March, just before the spring growth surge, using fresh houseplant or soil-based compost. Combine it with the annual prune. Move to a pot one size larger if roots are coming through the drainage holes or the plant wilts between normal waterings in summer; otherwise, refresh the compost and return it to the same pot. Water lightly until new growth appears, and wait six to eight weeks before the first feed so tender new roots are not burned.

• Roots grow through the drainage holes
• The plant wilts between normal waterings in summer
• New leaves are smaller than normal

Propagation

The RHS says softwood tip cuttings or semi-ripe cuttings taken in late spring or early summer root readily. Insert them in pots of sandy, peat-free cutting compost and give them bottom heat of 75 to 80°F (24 to 27°C) and high humidity, either in a heated propagator or with the pots enclosed in plastic bags on a warm windowsill. Pot rooted cuttings individually into 3½-inch pots and leave them undisturbed over the first winter. Cuttings are also the only way to keep a favorite named flower color.

Methods: Softwood tip cuttings, Semi-ripe cuttings · Best season: late spring or early summer.

Common problems

Bud drop is the complaint behind most questions about hibiscus. NC State notes that the plant is sensitive to environmental changes, so moving it can cause leaf and bud drop, and the RHS adds that in winter, buds and leaves yellow and fall because indoor light is low, a semi-dormant state the plant survives if watering is reduced. Pests are the other big issue. The RHS names aphids, red spider mites and glasshouse whitefly, UF/IFAS adds mealybugs and recommends insecticidal soaps or horticultural oils, and warns never to use the insecticide malathion on hibiscus.

Not sure which one it is? Try the plant problem diagnosis tool →

Is the hibiscus toxic to cats and dogs?

The ASPCA lists hibiscus as non-toxic to cats, dogs and horses. One caveat deserves mention: the ASPCA's hibiscus entry, and its separate Rose of China entry, are both filed under the scientific name Hibiscus syriacus, the hardy rose of Sharon, although Rose of China is a common name of the tropical species. There is no entry for Hibiscus rosa-sinensis by its own name. NC State flags no poison hazard for it either. A pet that eats a lot of any plant can still have an upset stomach, so keep fallen flowers swept up and call your veterinarian if symptoms appear.

Check any other plant against the ASPCA lists →