How to grow Queensland Arrowroot in New Zealand

Where to plant

Plant in deep, rich, well-drained soil in sun or part shade, in a spot where the clump can be kept in check. Canna indica spreads by rhizomes and by seed carried by water, and Weedbusters lists it as a weed that forms dense stands in wetlands, stream margins, gullies and coastal areas in frost-free districts. Never plant it near a stream, wetland or bush edge, and check your regional council's pest plant rules before planting.

• Northland and Auckland: grows well as a summer clump in frost-free gardens. Plant in October or November.
• Waikato and Bay of Plenty: marginal. Coastal Bay of Plenty only; plant in November and mulch the clump well before winter.
• Central North Island, Wellington, Nelson and Marlborough, Canterbury, Otago and Southland, and Central Otago: our calendar marks these as unsuitable, as frost and cold winters kill it back or stop it returning.

How to plant

1. Plant pieces of rhizome, each with a bud, about 10 cm deep after the last frost.
2. Work compost through the soil first, as the plants are hungry and grow fast.
3. Water in and keep the soil moist while shoots appear.
4. Space plants about 1 m apart, and edge the bed or plant in a large sunken container to stop rhizomes spreading.

Watering and feeding

Established plants tolerate dry spells, but regular watering in summer gives larger rhizomes. A mulch of compost in spring feeds the clump.

Pruning and care through the year

• Cut off the flower stems before the seed capsules ripen, to stop seed spreading.
• Cut the leafy stems for compost or poultry fodder through summer.
• Dispose of unwanted rhizomes and plant waste at a refuse transfer station, not in green waste dumped in the open, as pieces regrow.

Harvesting

Rhizomes can be dug from about six months after planting, when they are tender, but most are harvested at 8 to 10 months, when they reach full size. Dig the clump, shake off the soil and cut the rhizomes from the stems. They keep well in the ground, so dig as needed, as dug rhizomes do not store for long.

Growing in pots

A large pot at least 50 cm wide is a good way to grow arrowroot, as it keeps the rhizomes contained. Use a rich potting mix, water regularly in summer, and in cooler districts move the pot somewhere frost-free over winter.

Using it

The rhizomes are starchy and are eaten cooked, and the starch is used as a thickener. The large leaves are useful as bulk for the compost heap and as green feed for poultry.

Propagation and saving seed

Grow it from rhizome pieces or tips planted in spring. Large clumps can be divided in spring before new shoots appear. It also grows from seed, which is why the seed heads should be removed.