Arrowroot

Canna edulis is a tropical root crop closely related to ornamental cannas, producing large starchy tubers beneath bold, decorative foliage. The tubers can be cooked as a vegetable or processed into arrowroot starch used as a culinary thickener. It thrives in full sun with consistent moisture and does not tolerate drought or frost. Best suited to sheltered, warm garden positions or the edge of a subtropical food forest.

Growing

Start tubers or rhizome sections indoors once nighttime temperatures stay reliably above 10 °C, or plant directly outdoors once soil reaches 18 °C. Set divisions 5 cm deep and space plants 60 cm apart. Choose a sunny or lightly shaded spot with free-draining but moisture-retentive soil. In cooler climates, start tubers under cover 4–6 weeks before conditions are warm enough to plant out.

Care

Water consistently throughout the growing season — Canna edulis does not tolerate drought. Apply a balanced fertiliser every 4–6 weeks during active growth, or mulch heavily with compost to maintain soil moisture and provide nutrition. Remove spent flower stems to direct energy into tuber development. In frost-prone areas, lift and store tubers before the first frost event.

Harvest

Harvest tubers once the above-ground growth begins to yellow and die back, typically 6–9 months after planting. Dig carefully around the clump with a fork to avoid slicing tubers. Tubers can be left in the ground longer in frost-free climates to increase size. Leave some small tubers in the ground to regenerate the following season.

In the kitchen

Tubers require extended cooking — boil, steam, or roast until fully tender, which may take significantly longer than potato. They have a mild, slightly sweet flavour and starchy texture. Alternatively, grate and rinse the raw tuber repeatedly in water, then dry the settled starch to produce pure arrowroot powder, ideal as a clear-setting thickener for sauces and glazes.

Storing

Store lifted tubers in a cool, dry, frost-free location packed in barely damp sand or sawdust for up to several months. Cooked tubers keep refrigerated for up to 3 days. Dried arrowroot starch stores in an airtight container in a cool, dark cupboard for up to 12 months.