Aloha Hibiscus

Hibiscus adds a touch of tropical flair to your garden.

Hibiscus syriacus, Rose of Sharon. Picture: Getty Images

If you think of hibiscus, you might conjure an image of large, brightly coloured blooms and tag an association with Hawaii. They would be Hibiscus rosa-sinensis, aka tropical or Hawaiian hibiscus, thought to originate from southern China and South-East Asia. The species name translates as rose of China and although originally red, decades of breeding has produced thousands of registered cultivars in a dazzling range of colours.

The genus Hibiscus is in the mallow (Malvaceae) family, which includes cotton (Gossypium), okra (Abelmoschus), cacao (Theobroma), and Chinese lantern (Abutilon). Hibiscus covers more than 300 tree, shrub, perennial and annual species, many with a similar flower shape.

In Hawaii, the six native species include the yellow H. brackenridgei, the state flower. Australia has about 40 species, mostly from the tropical north and arid centre. Our native rosella, H. heterophyllus, is found all the way up the east coast but can grow in cooler areas with a warm microclimate. It quickly becomes a rounded shrub of 3-5m tall, with prickly branches and variable, long leaves. The large, nectar-rich flowers tend to be yellow in the north, and white or pink in the south, with a deep red centre.

H. tiliaceus (Talipariti tiliaceum; coastal hibiscus or cottonwood), is familiar as a small tree with yellow flowers and heart-shaped leaves. It’s found behind beaches along the east coast but is increasingly popular as a street and home garden tree (especially the purple-leafed ‘Rubra’) for its rapid growth and ability to take salt, wind and poor, sandy soil. In good urban conditions it can reach 8m, but is readily pruned.

Also called rosella, Hibiscus sabdariffa from tropical Africa has flowers that are added to sparkling drinks, tingeing them a soft pink. Jars of rosella in syrup contain the fleshy red calyx that develops after the flower petals have fallen; dried calyces are used in tea. It is grown as a short-lived, 1.5-2m-tall shrub in frost-free climates and an annual in colder areas.

Hibiscus mutabilis or cotton rose is fascinating as its large blooms, borne from late summer to autumn, open white in the morning, turn pink by noon and deep red by evening, staying on the plant for several days. It’s a fast-growing, partly deciduous, rounded shrub to about 4m tall from south-east China. Choose the double ‘Flora Plena’ as the single one is showing some weed potential around waterways near Brisbane.

If you live in a colder climate, try Hibiscus syriacus or Rose of Sharon (pictured), South Korea’s national flower. It’s an upright deciduous shrub of 2-5m with smaller flowers; summer blooms can be double or single in white, mauve or pink.

Good to know

For most hibiscus species, individual flowers last only a day or two but there is a constant succession through the warm months.

Tropical hibiscus like full sun, no frost, ample water and regular doses of rose or citrus fertiliser. Prune in late winter/early spring by about a third.

Small beetles cause holes in flowers and leaves. Control with traps of white or yellow plastic containers of water and detergent, or spray with pyrethrum.

Q&A

My four olive trees bear thousands of buds but I get only 30-40 olives per tree. Is there a remedy? Max Strahan, Sorrento, Vic

Olives flower profusely but not all flowers develop into fruits. Olives do best in a Mediterranean climate: hot, dry summers and cool winters. In milder, coastal areas, fruiting is reduced; in tropical climates they rarely fruit at all. They require cross-pollination from a second variety for reliably good crops.

I try to mix one part worm castings to three parts clay soil but it’s difficult to disperse them evenly. Are there other ways? Greg Horne, by email

Vermicast is a wonderful soil improver, adding organic matter and boosting microbial activity. Adding 10 per cent by volume is sufficient. It will not burn roots. You can apply castings to the soil surface without digging in if you water in and cover them with a soft mulch such as compost, pea straw or sugar cane mulch. Making them into a liquid solution is another option.

How do we remove agapanthus seedlings from our lawn? Jasmine, Adelaide

Hand weeding is best but is easiest when the soil is moist and seedlings are small. Use an old, blunt knife or a weeding tool to help lever them out. To avoid agapanthus seeds forming, cut off flowering stems at the base as soon as flowers fade.

November’s prize

Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. The best question for November wins two copies of Paul Bangay’s new book Stonefields by the Seasons. October’s winner is Shah Ramamurthy for his bulb question.