Plant Doctor Archive

My hibiscus flower too late

I HAVE several hibiscus plants - three in pots and one in the garden. They all develop buds and start flowering so late in the season that the winter weather tends to damage the flowers. Is there anything I can do to make them flower earlier in summer? They get almost full sun all summer, but are shaded between May to September. And since they are fairly small, young bushes, I haven't pruned them hard yet. I have a similar problem with my Bambino bougainvilleas - they flowered well the summer I bought them, but despite full sun in summer they're now refusing to flower. The only fertiliser I have used is sulphate of potash.

HIBISCUS produce flowers on new growth and, like many other subtropical plants, they often don't start putting on new growth until soil temperatures have really warmed up in summer. Placing them in a warm, sunny spot as you have done is good, but to encourage growth as early as possible you could also try regular applications of liquid fertiliser, or a slow-release type applied in early spring, along with regular watering if the mix dries out.

Another trick worth trying could be to use dark coloured containers which absorb heat, so warming the root system, which will encourage earlier growth. Or place some dark rocks nearby to soak up the heat during the day and act as radiators at night.

With bougainvilleas the secret is to be tough - if they're in pots, don't fertilise them unless they look really nutrient-deficient. Only water them when really dry and expose them to as much hot sunshine as you can. If planted in the garden, don't feed at all and don't water them unless wilting badly. The harsher the conditions, the better they flower, but flowering does also improve with age.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.