How to Grow Mashuas

Quick Facts

Factor	Value
Drainage	Moist but well-drained (RHS); Cultivariable: tolerates poor soil, loose/light soil best for harvest, moderately acidic.
Lifecycle	Tuberous, climbing perennial. Cultivariable gives USDA zone 9a as the best fit, noting about half the tubers survive a multi-day freeze at 25°F.
Edible parts	tubers, leaves, flowers
Documented problems	4 diseases, 7 pests

At a Glance

Diseases

Bacterial tuber staining (mashua, causal agent not yet confirmed)

low

Named only vaguely by Cultivariable (brown bacterial staining in wet, warm soil), no species identified -- generic entry created rather than guessing a pathogen.

Cucumber mosaic virus

low

Cucumber mosaic virus (CMV)

Mostly mild or asymptomatic in North American stock per Cultivariable.

Powdery scab

low

Spongospora subterranea

Raised or sunken scabby patches on tuber/root skin

Named specifically by Cultivariable as powdery scab (Spongospora subterranea).

Mashua virus diseases (potyviruses and Papaya mosaic virus, unspecified)

low

Covers Cultivariable's potyviruses (possibly Bean Yellow Mosaic, Turnip Mosaic, or unidentified mashua-specific strains) and Papaya mosaic virus, grouped since neither is singularly confirmed.

Pests

Glasshouse red spider mite (two-spotted spider mite)

low

Tetranychus urticae

Named by RHS for UK growing.

Glasshouse whitefly

low

Trialeurodes vaporariorum

Named by RHS for UK growing.

Cabbage white butterfly

moderate

Pieris spp.

Named by Cultivariable; larvae feed on the foliage.

Aphids

low

Aphididae (various spp.)

Named by Cultivariable.

Flea beetles

low

Chrysomelidae: Alticini (various spp.)

Named by Cultivariable.

Mice

low

Muridae (mice, various spp.)

Named by Cultivariable as "field mice," damaging tubers.

Deer

high

Cervidae

Named by Cultivariable as the single most serious mashua pest.

Growth Stages

1. Planting (BBCH 0): Cultivariable: plant whole or cut tubers (each piece at least 1/2oz with two or more eyes) 2-3in deep after frost danger passes, 30in row spacing; give the climbing stems support to grow up. RHS: propagate 'Ken Aslet' by division of the tuberous rootstock.
2. Climbing growth (BBCH 3): RHS: grow in full sun or partial shade, sheltered, moist but well-drained soil; wear gloves when handling, as the plant is a skin allergen. Cultivariable: performs best where summer highs stay below 80°F, with afternoon shade helpful in hotter spells.
3. Day-length triggered tuber formation (BBCH 4)
4. Harvest and overwintering (BBCH 8): Cultivariable: tubers need about 10 weeks after formation to size up, harvested around mid-November. RHS: lift and store tubers somewhere frost-free over winter, or grow the plant in a deep container that can be moved indoors.

Harvest & Storage

When to pick: Cultivariable: tubers need about 10 weeks after formation to reach good size, harvest falling around mid-November; colour develops late, so fully coloured varieties benefit from maturing as long as possible before frost.

Storage

Tubers keep 6-8 weeks at room temperature, or up to 8 months at 35-38°F/95% humidity; can also be frozen chuno-style for longer preservation (Cultivariable).

Sources

1. Cultivariable (specialist Andean roots and tubers breeder/grower resource) - Mashua (Tropaeolum tuberosum) growing guide

   Light: full sun in mild climates, afternoon shade where temperatures often exceed 80°F; needs cool summers (ideally not above 80°F). Soil: tolerates poor soil, loose/light soil best for harvest, moderately acidic, minimal fertiliser needed. Size: 8-12ft climbing height given support, tubers 3-8in (to 13in). Hardiness: USDA zone 9a (20-25°F), ~50% of tubers survive a multi-day freeze at 25°F; does well in the maritime Pacific Northwest. Day length: most varieties need ~13h critical day length, tuber formation starting early September; 'Ken Aslet' has a longer critical day length, tuberising mid-summer. Planting: whole or cut tubers (min 1/2oz per piece, 2+ eyes) 2-3in deep after frost, 30in row spacing; seed started 3+ months ahead at 55-65°F. Propagation: vegetative (tubers/cuttings) or seed (not true to type), hummingbird/bumblebee pollinated. Pests: deer (most serious), cabbage white butterfly larvae, flea beetles, aphids, field mice; bears/waterfowl can destroy plantings. Diseases: potyviruses (possibly Bean Yellow Mosaic, Turnip Mosaic, or mashua-specific strains), Cucumber Mosaic Virus, Papaya Mosaic Virus (mostly mild/asymptomatic in North American stock); powdery scab (Spongospora subterranea); bacterial brown staining in wet, warm soil. Harvest: tubers need ~10 weeks after formation, around mid-November; colour develops late, so full-colour varieties benefit from maturing as long as possible before frost. Storage: 6-8 weeks at room temperature, up to 8 months at 35-38°F/95% humidity; can be frozen (chuno-style) for longer preservation. Edible use: all parts edible -- tubers cabbagey when cooked (raw tubers unpleasant, glucosinolates), leaves a spicy mustard-like salad green, flowers sweet with aniseed notes; high in vitamin C, contains isothiocyanates.

These source is specific to this region. The full list of 2 sources behind this guide (Cultivariable (specialist Andean roots and tubers breeder/grower resource), Royal Horticultural Society) is in the references of our UK guide to mashua; they describe the plant itself, which is the same wherever it grows.