A frost-tolerant Andean tuber with peppery, mustard-edged flavor that thrives in cool climates where most root crops struggle.
Tropaeolum tuberosum · also called añu, isaño
Windows are counted from the average date of your last spring frost.
Mashua is one of the most productive tubers per square foot in cool, short-season gardens and requires almost no fertilizer. Its trailing stems also produce edible flowers, giving the bed ornamental value through the growing season.
A little history. Native to the Andes from Colombia to Bolivia, where it has been cultivated above 10,000 feet for at least 1,500 years according to archaeological records. Tubers contain glucosinolates — the same sulfur-based compounds found in mustard — which account for the sharp raw flavor and diminish substantially with cooking.
Sow seeds 4 inches (102 mm) deep, and aim for 18 inches (45 cm) between plants once thinned. Plant tubers 3–4 inches deep and keep soil evenly moist; shoots are slow to emerge — do not assume failure before 4 weeks. Seedlings emerge in 14–28 days.
Beds strongly preferred — tubers spread widely and need 12 inches of loose soil depth; containers restrict yield significantly. In containers: 15-gallon pot minimum, at least 14 inches deep.
Water deeply once or twice a week during active growth; reduce once tops begin to yellow in autumn. Water when the top 2 inches of soil feel dry to the touch. Aim for about 1 inch per week including rain.
Apply a single side-dress (scatter fertilizer along the row and water in) at planting; avoid heavy feeding mid-season. What to use: low-nitrogen compost or a 2–5-5 organic blend; excess nitrogen drives leaf growth at the expense of tubers.
Pinch out the leading shoot tips once vines reach 18 inches to encourage branching and redirect energy toward tuber development; remove any flower stems if maximum tuber yield is the goal.
It's ready when harvest after the first killing frost blackens the tops, or when foliage yellows and dies back naturally — tubers are at peak size and starch content at this point. Cut back dead tops to 2 inches, then loosen soil with a fork 8–10 inches out from the crown and lift carefully; tubers are brittle — work slowly to avoid snapping them.
Cure in a single layer in a cool, dry, airy space at 50–55 °F (10–13 °C) for 1 week, then store in slightly damp sand or paper bags at 40–50 °F (4–10 °C) for up to 4 months.
In climates with mild winters (lows above 20 °F (-7 °C)), tubers left in the ground may re-sprout; mulch heavily with 4–6 inches of straw after tops die. In colder climates, lift all tubers before hard ground freeze.
Nasturtium
Aphids often settle on nasturtium stems in preference to mashua shoot tips, which can pull colonies off the crop. Treat it as a sacrifice plant: cut off and bin loaded shoots rather than leaving them to breed more aphids.
Fava Bean
Fava beans bank nitrogen in root nodules that is mostly released the following season as the roots break down, so leave the stubble in place. Mashua is a light feeder and will not fight the beans for food in the meantime.
Spinach
Spinach feeds in the top few inches while mashua tubers form deeper, so the two rarely compete for water or food. The spinach is usually cut and cleared by early summer, well before the mashua vines run over the bed.
Cilantro
Let a few cilantro plants bolt (shift from leaf growth to flowering) and the flat flower heads draw in hoverflies and tiny parasitic wasps whose larvae feed on aphids, the main pest of young mashua shoots.
Potato
Both crops are hosts for late blight, and cool wet autumn weather is exactly when mashua is still in leaf. Growing them side by side lets spores move straight from one canopy to the other; keep them in separate parts of the garden.
Tomato
Tomatoes carry the same late blight that strips mashua foliage, and infected tomato vines left standing in late summer become a spore source right when mashua is sizing its tubers. Separate the two beds.
Easy-going — Mashua can grow almost anywhere in the rotation without a strict rest.
The pea and bean family, the cabbage family or the tomato family thrive in this ground next season.
Mashua is a light feeder and leaves the soil loose and in fair shape, but it gives little back, so work in compost after lifting. Wait at least 1 year before returning any nasturtium-family crop here. Legumes, brassicas, or nightshades follow well.
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