In the north Island, we revel in the sumptuous splash of flowering hibiscus for a large part of the year and their casual flamboyance is often taken for granted.
There are hundreds of varieties grown in New Zealand and, while many are quite tender and tricky, requiring extra care to thrive here, there are a surprising number that are pretty resilient and can be grown much further south if you give them what they need. The secret is to keep the roots warm and dry in winter.
Winters are never dry here, so the best way to control root temperature and moisture is in pots. Hibiscus are remarkably happy pot plants if kept in full sun, on a deck or patio, against a north-facing wall, out of the wind. They don t mind constricted roots as long as they feel the sun s heat through the pot and are fed regularly on rose or citrus fertiliser, both of which are high in potash and low in nitrogen. The pots should be a size that allows them to be easily moved around.
In summer they need plenty of moisture, but in winter they should be dragged out of the rain, under the eaves or into a sunny porch or hothouse to keep the roots dry. Never put a water tray under the pot in winter. They will tolerate cold temperatures down to just above freezing, but they won’t tolerate wet, cold roots.
A raised brick, stone or concrete garden bed against a masonry wall, on the north side of a house, can make a wonderful spot to grow hibiscus (or frangipani or bougainvillea), in a sheltered, sunny garden where they would not have a chance even a few metres away from the building. Fill the garden bed with light, sandy soil and some extra compost. It should drain quickly and stay warm with the stored heat in the masonry, while the eaves of the house will prevent most of the winter rain from reaching it.
Prune hibiscus hard in September, exactly as you would a rose bush. Every couple of years you should tip them gently out of their pots in September or October, remove two thirds of the old potting mix, along with half the roots, then repot into fresh potting mix. Keep them as warm as possible until new shoots start to grow.
The toughest, old-fashioned varieties tend to have smaller flowers than the big new hybrids, but these oldies produce far more blooms in a season and are much more resistant to disease. Toughest of all is Hibiscus rosa-sinensis ‘Red. Its bright red, 11cm flowers have a deeper red eye. This one would be my first choice if I lived in Nelson, Sumner or Banks Peninsula, and wanted to give hibiscus a shot. Agnes Gault is also remarkably tough, with 17cm, satiny pink blooms and great vigour.
Other real troupers are the shaggy, double pink ‘Suva Queen, the orange ‘DJ O’Brien, petite lilac-pink ‘Island Empress, flame coloured ‘Simmonds Red and the stunning golden-yellow ‘Fiji Gold. There are more, but these are the staunchest of all.
In the ground, hibiscus prefer sandy or light volcanic soil that drains quickly. In clays and clay loam they very often succumb to root rot unless you build up loose soil on top of the existing clay.
In cooler areas, the more tender hybrids can often still be grown successfully if they’re grafted onto hardy roots, such as ‘Suva Queen, Agnes Gault or ‘Red.
Please be aware the hibiscus varieties available, will vary by Mitre 10 store.