How to Grow Mashuas UK

When to Plant Mashuas in the UK

When to plant mashuas in the UK: in Southern England, sow early May to early June. Find your area in the table below.

Region	Sow
Southern England	early May to early June
Midlands	early May to early June
Northern England	early May to early June
Scotland	mid May to early June

Southern England - detail & sources

Cultivariable states planting is done after frost danger passes; taken here as May for southern England.

Midlands - detail & sources

Same after-frost planting window as elsewhere in the UK.

Northern England - detail & sources

Planting window opens about a week later than southern England for a later last-frost date -- RHS rates 'Ken Aslet' H3, only reliably hardy in coastal and relatively mild UK areas, so exposed northern sites may do better with container growing and indoor overwintering.

Scotland - detail & sources

Planting window opens about two weeks later than southern England for Scotland's later last-frost date -- RHS's H3 rating makes reliable outdoor overwintering unlikely here, so lifting tubers or growing in a movable container is the safer approach.

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. RHS rates the 'Ken Aslet' garden form H3 (-5 to 1°C), hardy only in coastal and relatively mild parts of the UK. 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

At a Glance

Growth Stages

Stage	BBCH	Notes
Planting	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.
Climbing growth	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.
Day-length triggered tuber formation	4	Cultivariable: most mashua varieties are short-day plants, needing a critical day length of around 13 hours before tubers begin forming in early September -- the RHS-favoured 'Ken Aslet' cultivar has a longer critical day length, tuberising earlier in mid-summer, which likely explains its popularity as the standard UK garden form.
Harvest and overwintering	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).

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)

Named specifically by Cultivariable, alongside potyviruses and Papaya mosaic virus; RHS separately gives a general virus-susceptibility warning for the UK garden cultivar. Mostly mild or asymptomatic in North American…

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.

Mashua, Seed to Harvest

Orange flowers with red spurs

RHS describes the AGM-winning 'Ken Aslet' cultivar's flowers as orange with brown veining and red spurs -- a close relative of garden nasturtiums.

Striped yellow tubers

Cultivariable notes mashua tubers range from 3-8in, occasionally longer -- the black striping on yellow skin is a common colour pattern.

Purple and cream tubers

Cultivariable notes colour develops late in the growing season, so fully coloured varieties benefit from as long a season as possible before frost.

A climbing habit

Cultivariable gives a climbing height of 8-12ft given something to grow up -- RHS's 'Ken Aslet' reaches a slightly more modest 2.5-4m in UK gardens.

A named Peruvian cultivar

'Yawar Waqay' (Quechua for 'crying blood') is one of many named mashua cultivars maintained by Andean growers, reflecting the crop's long cultivation history.

A wide range of tuber colours

Andean growers maintain dozens of mashua varieties, selected over centuries for colour, flavour and yield.

Foliage and flowers together

The rounded, lobed leaves are typical of the wider Tropaeolum genus, which also includes the common garden nasturtium.

Trellis-grown vine

RHS recommends a sunny wall or similar support for 'Ken Aslet' -- the climbing habit needs something to scramble up to perform well.

Tuber surface detail

Cultivariable notes raw tubers taste unpleasant due to glucosinolates, but become 'cabbagey' and palatable once properly cooked.

References

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.

2. Royal Horticultural Society - Tropaeolum tuberosum 'Ken Aslet' (nasturtium)

   Hardiness H3 (-5 to 1°C, coastal and relatively mild parts of the UK). Soil: clay, loam, sand, moist but well-drained, acid or neutral pH. Sun/aspect: full sun or partial shade, any aspect. Exposure: sheltered. Size: 2.5-4m height, 0.5-1m spread, 2-5 years to maturity. Propagation: division of the tuberous rootstock. Pests: glasshouse whitefly, red spider mite. Diseases: susceptible to virus diseases affecting vigour. Safety: skin allergen, wear gloves when handling. Notable: AGM-winning cultivar, orange flowers with brown veining and red spurs; earlier-flowering with bluish foliage, grows well in Britain on a sunny wall. Overwintering: lift and store tubers frost-free, or grow in a deep container overwintered indoors.

2 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.