Hibiscus

By Jennifer Stackhouse

Tags: care, erinose mite, hibiscus, hibiscus flower beetle, Jennifer Stackhouse, pests and diseases, Sooty Mould, summer flowering

The flamboyant flowers of hibiscus (Hibiscus rosa-sinensis) light up summer gardens. They are such generous shrubs unfurling new flowers day after day so there’s always something bold and colourful to enjoy amid the dense green of our summer gardens. With flowers in tones of red, pink, yellow, orange and even purple, and single or double, choosing a favourite is one of the hardest decisions to make when buying a hibiscus for the garden.

Oriental origins and care

Hibiscus flowers conjure up memories of tropical-island and beachside holidays and indeed they are often called Hawaiian hibiscus. Despite this common name, these shrubs are native to China. Their oriental origins are recorded in the species name of ‘rosa-sinensis’, which means ‘rose of China’ in botanical Latin.

It isn’t a bad idea to think of hibiscus as roses as they respond to the same care roses demand. They need full sun and thrive on regular feeding (apply rose food every six weeks from spring to late summer). They also benefit from a 5mm layer of organic mulch mixed with composted cow manure, deep watering and a hard prune in late winter or very early spring. Cut back by about a third.

Hibiscus shrubs shine through the warmer months of the year so work well planted around outdoor summer features such as swimming pools or sunny terraces. They grow well in the ground but some compact varieties also suit pots. The shrubs range from compact metre-high shrubs (great in pots or beside the path) to large shrubs 2-3m high.

During winter hibiscus lose their leaves and hunker down. These vibrant subtropical plants don’t tolerate heavy frost. In areas with very cold frosty winters, grow hibiscus in a warm, frost-free microclimate such as against a warm, north-facing masonry wall, or in large containers so they can be moved into a frost-free position over winter.

Troubleshooting

In subtropical climates hibiscus are attacked by a minute insect called erinose mite. This little insect is invisible to the naked eye but distorts the leaves with blistered lumps that are very easy to see. Control this pest by pruning off damaged growth and disposing of it in a sealed bag in the rubbish.

As the flowers form, hibiscus flower beetle may chew holes in petals to access pollen. They cause flower buds to drop. The beetles are black, small (just 3mm long) and very hard, which makes them difficult to squash. Imidacloprid (sold as Confidor and MaxGuard) is registered against this pest but is not recommended for use on flowering plants where bees are present.

There are several simple non-chemical control measures that reduce beetle numbers. These include collecting and disposing of spent flowers (put them in a bag and in the garbage bin) and using a trap under affected plants in the form of a white plastic container filled with water and a few drops of detergent. The white colour appears to attract the beetles that then drown in the water.

Black sooty mould that may appear on the leaves is triggered by aphids that are feeding on new growth or around the base of buds. Control aphids (squash or use low-toxicity insecticide). Soap sprays such as Natrasoap control aphids and help remove sooty mould.

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Jennifer Stackhouse

Jennifer Stackhouse

Horticulturist, garden writer, blogger & editor.