Mashua

Mashua (Tropaeolum tuberosum) is a climbing relative of the garden nasturtium from the Andes, where it is grown as a root crop alongside potatoes, oca and ulluco. The stems climb by wrapping their leaf stalks around anything they touch and reach 6 to 10 feet in a season. The leaves are round with three to five shallow lobes, and the long-spurred, tubular flowers are orange to red with yellow, hanging on long stalks. Underground it forms cone-shaped tubers in yellow, white, red or purple, often streaked or mottled.

The catch: day length

Most mashua is a short-day plant. It doesn't flower or start forming tubers until days shorten in early fall, and the tubers then need several frost-free weeks to size up. Where hard frost arrives in September or early October, you may get a big vine and few or no tubers. It does best where autumns are long and mild and summers are not too hot: the Pacific Northwest coast and northern California are ideal. In hot, humid summers it struggles.

'Ken Aslet' is a day-neutral selection that flowers from midsummer, so it is the one to grow if you want flowers before frost.

Planting and growing

• When: plant tubers around your last spring frost date. Check yours with our zone and frost date lookup.
• How: about 3 inches deep and 2 to 3 feet apart, next to a fence or trellis at least 6 feet tall. See our guide to supporting garden plants.
• Where: full sun in cool-summer areas, light afternoon shade where summers are warm. Loose, well-drained soil that you keep evenly moist through dry spells.

Harvest and storage

Dig the tubers after frost blackens the vines; a light frost doesn't hurt tubers underground, but dig before the ground freezes. Store them like potatoes, somewhere cool, dark and slightly humid, and keep a few of the best for replanting in spring. In zone 8 and warmer, tubers can stay in the ground under mulch and will resprout, which also means any tuber you miss comes back next year.

Raw mashua has a sharp, peppery, mustard-like bite. Cooking mellows it a great deal, and in the Andes the tubers are often left in the sun for a few days before cooking to sweeten them. Use them roasted, in soups and stews, or thinly sliced raw in small amounts.

Wildlife

In its native range mashua is pollinated by hummingbirds, and they visit it in North American gardens too. With short-day types, though, the flowers often open after most hummingbirds have migrated south. Butterflies show little interest.