Mashua

Mashua is a climbing vine that produces edible tubers, edible leaves, and edible flowers, repels certain insects and nematodes by volatilizing compounds into the surrounding air, and looks genuinely beautiful on a trellis from mid-summer through frost. It is also almost completely unknown in the United States outside of Andean immigrant communities and a small community of specialty crop growers. That combination - real utility plus obscurity - is exactly why it fetches $8-15/lb when someone actually has it to sell.

The flavor catches people off guard. Raw mashua tastes sharp, peppery, and slightly bitter in a way that reads almost medicinal. Cooked mashua tastes mild and starchy with a hint of sweetness. These are not variations on the same theme - they are entirely different eating experiences produced by the same root. Understanding why makes you a better cook and a better grower.

What it actually is

Tropaeolum tuberosum is the tuberous nasturtium, a close relative of the common garden nasturtium (T. majus) familiar from flower beds everywhere. The common nasturtium produces no significant root; mashua puts that family’s energy underground, producing tubers 2-6 inches long with waxy, yellow-to-orange-to-red skin, sometimes streaked with purple. Above ground, the plant is a vigorous climbing vine that reaches 6-8 feet, producing lobed leaves and vivid orange and yellow flowers from late summer until frost. The Incas called it mashua or añu and grew it extensively throughout the Andean highlands alongside oca and ulluco as part of a traditional tuber polyculture.

Every part of the plant is edible. The tubers are the main harvest. Young leaves and shoots can be eaten in salads or as a cooked green. The flowers have the mild, slightly peppery character of common nasturtium flowers and are used as an edible garnish.

The plant grows as an annual in most of the US. In its native Andean range, it thrives at 9,000-13,000 feet elevation in cool temperatures - frost-tolerant above ground as a seedling but the tubers need to form before hard frost arrives. In North American garden conditions, the growth pattern most closely resembles oca: slow early growth, accelerating in late summer, with tuber bulking tied to shortening day length in fall.

The ROI case

The seed cost is higher than most vegetables: $12.99 for a 6-count tuber packet from specialty Andean crop suppliers like Cultivariable or Strictly Medicinal Seeds. That’s the full input cost. Mashua has no significant pest or disease pressure in North American gardens, needs no fertilizer beyond basic soil preparation, and requires no irrigation beyond 1 inch per week.

A standard 6-tuber planting in good soil, allowed to run on a trellis with a full season, yields 4-8 lb of tubers. Five pounds is a conservative midpoint.

Planting	Yield	Price scenario	Gross	Seed cost	Net
6 tubers	5 lb	Farmers market ($10/lb)	$50.00	$12.99	$37.01
6 tubers	5 lb	Specialty market ($8/lb)	$40.00	$12.99	$27.01
6 tubers	7 lb	Farmers market ($10/lb)	$70.00	$12.99	$57.01

Year 2+ seed cost: $0. Mashua tubers store well through winter (same conditions as potatoes - cool, dark, dry) and replant directly in spring. Save 6 of the best tubers from your harvest and you’ve eliminated the only recurring input cost.

The ornamental case is real. Mashua on a trellis or fence produces months of vivid orange flowers and dense climbing foliage. It earns its garden space on visual grounds alone before accounting for the harvest.

Growing requirements

Season: mashua needs 180-220 frost-free days for a full tuber harvest. This is a genuine constraint in zones 5-6, where the frost-free window runs roughly 150-170 days. Row cover in fall extends the season 2-3 weeks - and those weeks matter, because tubers bulk heavily in September and October as days shorten. In zones 7-9, timing is less critical and yields are generally higher.

Starting: plant tubers outdoors after last frost, 4-6 inches deep, 12-18 inches apart. Mashua does not benefit meaningfully from indoor starting - the tubers prefer to establish in cool spring soil rather than a warm indoor container. In zone 5, plant as early as the soil is workable and the threat of hard frost has passed.

Support: provide a trellis, fence, or wire frame. The vine climbs by twining and reaches 6-8 feet. Without support it sprawls horizontally and produces a tangled, difficult-to-manage ground cover. On a vertical structure it is clean, dense, and beautiful. A simple cattle panel arch or 6-foot wooden trellis handles it well.

Soil: loose, moderately fertile, well-drained. Mashua is not demanding - it evolved in high-altitude Andean soils that are relatively lean. Avoid excessive nitrogen, which drives vine growth at the expense of tuber formation. A modest compost amendment at planting is sufficient; no supplemental fertilizer is typically needed.

Water: 1 inch per week through the growing season. Consistent moisture produces better tubers than boom-bust irrigation cycles. Reduce watering slightly in September and October as the plant shifts energy to tuber development. Mashua tolerates brief drought better than oca but worse than potato.

Day length response: mashua is a short-day crop. Tuber initiation is triggered by day lengths below approximately 12 hours, which occurs after the autumn equinox. This is the same response that governs sweet potato and oca tuber formation. The practical implication is that you cannot hurry it: the vine will grow vigorously all summer, then switch into tuber mode in fall. Late-season frost protection (row cover or low tunnel) becomes important precisely when the plant is doing its most productive work.

Pest-repelling properties

Mashua contains glucosinolates and isothiocyanates - the same class of sulfur-containing compounds found in mustard, horseradish, and arugula. These compounds volatilize from the plant’s tissues and have demonstrated repellent effects on some insects and nematodes in the root zone. Research published in pest management literature and referenced by ATTRA (National Sustainable Agriculture Information Service) identifies mashua as a functional companion crop for use alongside potato and oca, where it may reduce aphid pressure and suppress root-knot nematode populations.

This is not folk superstition about “good companions.” There is a documented chemical mechanism: isothiocyanates are the same compounds used in commercial biofumigant treatments derived from mustard seed meal. Mashua releases them continuously from living tissue.

Traditional Andean polycultures interplant mashua with potato and oca specifically for this reason. A border planting of mashua around a potato bed, or alternating mashua plants within an oca row, applies the same principle. The pest suppression is partial - not a substitute for scouting and management - but it is real and quantifiable.

The raw vs. cooked distinction

This matters enough to address directly. The glucosinolates and isothiocyanates responsible for mashua’s pest-repelling properties are also responsible for its raw flavor. Bite into a raw mashua tuber and you get a sharp, peppery, slightly bitter heat. It reads somewhere between horseradish and radish. Some people find it interesting in small amounts; others find it unpleasant as a straight raw vegetable.

Heat at or above 180°F hydrolyzes these compounds. A fully cooked mashua tuber - boiled, roasted, or steamed - has a mild, starchy flavor with a subtle sweetness. The transformation is not subtle. You would not identify cooked mashua as the same vegetable from flavor alone.

A second path to reducing raw pungency: sun-sweetening after harvest. Leave freshly dug tubers in indirect sunlight for 3-5 days before eating. The same post-harvest treatment used for oca reduces glucosinolate concentration and converts starches toward sugars. The result is a milder raw flavor and a noticeably sweeter one. Traditionally, this is the preferred preparation in the Andes for fresh eating.

If you’re serving mashua to people unfamiliar with it, cook it first. The mild, starchy cooked form is an accessible introduction. The raw, sharp form is an acquired taste.

What goes wrong

Short season in zones 5-6: tubers remain small if frost arrives before the plant has had adequate time post-equinox to bulk them. Prioritize row cover deployment in late September. Even a simple layer of floating row cover across the trellis can provide 4-6 degrees of frost protection and extend the effective season into early November in most of zone 6.

Vine without support becomes a mess: mashua will sprawl across surrounding plants if not given vertical structure early. Install the trellis at planting time, before the vine needs it. Trying to redirect an established 6-foot mashua vine in July without damaging it is frustrating.

Expecting potato-like yields: mashua is a specialty crop. Five pounds from six tubers is a realistic, good outcome - not a disappointment. Managing expectations matters because the vine grows with such vigor all summer that first-time growers often expect a proportionally large harvest. The vine and the tubers are on different schedules.

Harvesting before frost-sweetening: mashua tubers are technically harvestable after the first frost kills back the foliage, but flavor improves if you allow the tubers to remain in the ground for a week or two after light frost (above 28°F). Harder frosts damage the tubers; light frosts do not. Monitor the forecast and harvest before temperatures drop below 28°F consistently.

Harvest and storage

Harvest after the first light frost kills the foliage, which is the signal that the plant has finished its above-ground growth cycle. Cut the vines back and dig with a fork, working outward from the plant base. Mashua tubers tend to cluster more tightly than oca but extend further than potato - check a 12-inch radius around the main stem before calling a plant finished.

Brush off soil and cure at room temperature for a few days before storage. Sun-sweetening (3-5 days of indirect light) at this stage reduces raw pungency if you intend to eat any portion raw.

Storage conditions: cool (40-55°F), dark, with moderate humidity and good air circulation. The same conditions appropriate for potato work well. Do not refrigerate below 40°F; chilling injury causes discoloration and off-flavors. Do not allow to freeze. Properly stored mashua keeps 3-4 months.

Saving planting tubers: select firm, unblemished tubers in the 2-4 oz range. These store as described above and replant directly in spring, with no special treatment needed beyond keeping them from drying out completely. Label them clearly so they don’t get cooked.

Kitchen use: beyond the sun-sweetened raw application, mashua works well roasted (400°F, 25-30 minutes, with olive oil and salt), boiled and mashed with butter and cream, or sliced thin and fried into chips. The mild starchy cooked flavor is versatile and pairs naturally with the acid and fat combinations that work well with potato. In Andean cooking, it frequently appears with oca in mixed stews where each tuber contributes distinct texture and flavor alongside a shared background of chili and aromatic herbs.

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Related reading: Oca - fellow Andean short-day tuber with similar timing and season extension needs; Potato - companion crop and traditional Andean polyculture partner