How to grow Arrowroot

Where to plant

Edible canna wants warm, sunny weather and moist, fertile soil, but does best in moderately hot summers. Long spells above about 90°F (32°C) slow it down, so in the desert give it steady water and afternoon shade. Frost kills the tops, and a hard freeze kills rhizomes left in frozen ground.

It grows all year in Hawaii and South Florida, and as a long season crop in Central Florida, Southern California, the Desert Southwest, Northern California and the Mid-South, where the clump can be mulched over winter or lifted before a hard freeze. Where the season is short, such as the Northeast, the Midwest and the mountains, it is grown more as an ornamental, with a small crop dug in fall. Sources differ on cool summer areas: our regional calendar treats Pacific Northwest summers as too cool for a worthwhile crop, while a Washington State grower reports good yields there after about eight months.

• Tall clumps blow over in strong wind, so plant along a fence or in a sheltered spot.

How to plant

1. Buy rhizomes sold as edible canna or achira from a food plant nursery. Most varieties are sterile and grown only from rhizomes.
2. Cut large rhizomes into pieces, or use the rhizome tips, each with at least one or two buds.
3. Plant about 3 to 4 inches (8 to 10 cm) deep in spring, once the soil has warmed, in soil dug over with plenty of compost.
4. Space plants about 2 feet (60 cm) apart in rows 3 feet (90 cm) apart, or a little closer in a block. Crowding gives smaller roots per plant but a big total crop.
5. Water in well. Shoots should appear in about two weeks.

Watering and feeding

Keep the soil evenly moist through the growing season, especially in hot, dry weather, and mulch deeply to hold moisture. Like garden cannas, it grows best in rich soil with regular feeding: dig in compost before planting and side dress with compost or a balanced fertilizer during summer.

Do not let the bed become waterlogged once growth slows in fall, as rhizomes sitting in cold, wet soil rot.

Pruning and care through the year

• Cut some of the older leaves through summer for mulch or poultry feed, but leave most of the foliage to feed the rhizomes.
• Where frosts are light, cut the frosted tops back to 6 to 8 inches (15 to 20 cm) and mulch heavily over the clump; it regrows in spring.
• Where the ground freezes, dig the clump before a hard freeze and save a few healthy pieces for replanting.
• Keep edible canna away from ornamental cannas if you can, as both carry canna viruses spread by aphids.

Harvesting

In warm climates the rhizomes can be dug from about five months after planting, and in cooler ones after six to eight months. They keep growing if left, but slowly become more fibrous. Unlike some root crops, they are at their best for eating straight out of the ground. Where the soil does not freeze, the best store is the ground itself: dig what you need and leave the rest.

Dug rhizomes are perishable. Kept at about 45°F (7°C) they last about three to four weeks. Peel and cook them like potatoes. They are mild and slightly sweet. The young shoots and leaves are edible too, and older leaves are used as food wraps.

Growing in pots

Edible canna grows in a large pot, at least 20 inches (50 cm) wide, which also makes it easy to move under cover in cold areas. Use a rich potting mix and water often, as the leafy clump drinks a lot in summer. Expect a smaller crop than in the ground.

Propagation and saving seed

Grow it from rhizome pieces or tips, which root and sprout readily. For a head start in short season areas, pot the pieces indoors in spring and plant them out once frost has passed. Seed is possible for the few fertile varieties, but it has a hard coat and germinates slowly and unevenly.