Mashua (Tropaeolum tuberosum) is a herbaceous, tuber-forming perennial vine related to garden nasturtiums. It's leaves and tubers can be enjoyed raw or cooked, and in the Andes, where it's been cultivated for thousands of years, mashua tubers are traditionally roasted, boiled, added to stews, fermented, or even used in desserts after curing.
Mashua has been cultivated at high elevations in Peru, Bolivia, and Ecuador and thrives in cool, moist climates where many other tubers struggle.
Mashua tubers have a distinctive flavour. When raw, they are crisp with a peppery and slightly radish-like heat, similar to the spiciness of nasturtium flowers. Cooked, they become tender and the flavour mellows to nutty, earthy, and faintly sweet.
For northern gardeners, mashua is especially appealing because it grows vigorously through cool summers and doesn’t demand heat to produce a crop. Vines can reach 6-12+ feet long each season, creating lush gardens and quick green screens.
PLANTING MASHUA
When to Start
- Mashua is grown from tubers, not seed.
- Start tubers indoors or in a greenhouse: late winter to early spring.
- Plant outdoors: after risk of hard frost, once soils have warmed slightly (8-10ºC).
- Mashua tolerates cool conditions but young shoots are frost-sensitive. In coastal BC, planting out late April–May works well.
Planting Position
- Plant tubers horizontally, 5–10 cm (2–4”) deep, with the sprout at the fat end pointing up (if visible).
- Space plants 30–45 cm (12–18”) apart in-ground, or grow one plant per 15–20 gallon container.
- Tubers can be pre-sprouted in pots to get a head start.
- Mashua is a climbing vine that cannot hold itself up off the ground without something to climb. Give it a trellis, fence, netting, or let it scramble through shrubs.
GROWING MASHUA
Site and Sun
- Plant in full sun to light shade.
- In hotter climates, it prefers afternoon shade, but in coastal areas full sun is usually fine.
- Mashua actually performs best where summers are cool and moist, with good air movement.
Soil
- Loose, well-drained soil with moderate fertility
- Rich in organic matter
- Avoid compacted or waterlogged ground
- Don't overfeed, especially with nitrogen - you'll get large vines but small tubers
Water
- Keep evenly moist, especially during active growth.
- Do not let the soil dry out completely.
- Mulching helps retain moisture and moderates soil temperature.
- Mashua produces a lot of top growth before forming tubers, so patience is key.
DAYLENGTH AND FLOWERING
Mashua is short-day sensitive. That means it only begins forming tubers as days shorten in late summer or early fall to approximately 12 hours of daylight, which usually falls around the fall equinox (Sept 22). That means tubers don't usually begin forming until late September.
Mashua isn’t just daylength-sensitive — it’s daylength + temperature sensitive:
- Short days + cool nights = strong tuber set
- Short days alone, with warm nights, give weaker tuberization
That means:
- Lots of vines produced early
- Tubers bulk up late in the season
Don’t panic if you don’t see results by midsummer — this is normal. This trait is exactly why mashua performs better in cool coastal climates than in hot continental ones.
HARVESTING
When to Harvest
Let the tubers size up as long as possible, but don't let them freeze.
- Harvest after frost kills back the foliage (or just before a hard freeze).
- Tubers are usually ready late October to November, though sometimes they make it to December in mild climates if frost is light.
- Dig gently — tubers form close to the surface and close to the base of the plant.
Washing
Washing the tubers after harvest is optional. Traditionally, they are not washed, but we prefer to wash ours before curing.
STORAGE AND CURING
Fresh mashua can be sharp or bitter. Traditional curing improves flavour.
Curing
- Expose harvested tubers to indirect light for 1–2 weeks, in a dry, frost-free location.
- This converts compounds that cause bitterness into sugars.
Storage for Eating
- Mashua tubers need similar conditions to potatoes, but cooler (8-12ºC) and not as dry.
- Properly cured mashua stores for several months.
- Traditional storage for eating would see unwashed, cured tubers stored in a dark, dry, cool location. Watch that they don't dry out or sprout early.
Storage for Replanting
- We like to wash and cure our tubers and then store them in a container in the fridge at approximately 3-5ºC (normal fridge temperatures).
- We check on the tubers every 1-2 weeks, opening the container to allow air exchange and to monitor humidity levels.
- This method allows us to monitor tuber health and keeps tubers firm.
- Tubers can also be stored in breathable containers of barely damp grow mix in a cool location (we use an unheated, insulated garage) - this is one of the easiest options for ensuring accurate moisture levels throughout storage, but they may sprout earlier than if kept in the fridge.
PESTS AND ISSUES
- Generally pest-resistant.
- Can act as a trap crop for aphids, similar to nasturtiums. Aphids will be most attracted to the growth tips.
- Deer and rodents tend to avoid it.
TIPS FOR SUCCESS
- Plant out in the spring after risk of frost and freezing, and harvest in the fall before the ground freezes.
- Provide a support structure.
- Provide consistent moisture, especially during tuber formation.
- Leave tubers in the ground as long as possible in the fall (without freezing), allowing the tubers to size up.
- Be gentle during harvest - the tubers are tender and have thin skin.
Mashua is productive, resilient, unusual, and deeply rooted in Andean culture and food history. It offers a flavour you won’t find in grocery stores and it fits perfectly into cool-summer, short-season gardens and food forests.