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How to Grow Ullucos UK | Regional Planting Calendar
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In the UK, ullucos go in the ground early May to early June.
Ullucos (Ullucus tuberosus) — Tender tuberous perennial grown as an annual.
Timing is the decision that matters most in the UK: there are 4 separate regional sowing windows, ranging from early May in Southern England to late May in Scotland.
Core growing advice on this page is checked against named horticultural sources — see References.
Cultivariable: plant tubers once frost danger has passed, roughly seven months ahead of the first expected autumn frost -- taken here as a May planting window for southern England's typically mild, maritime autumns, which give the short-day tuberization stage the best chance to run its course before hard frost.
Midlands - detail & sources
Planting window shifted about a week later than southern England for a cooler spring start. Honest caveat: the Midlands' typically earlier autumn frosts leave less margin for ulluco's late, short-day tuber bulking than the milder south and west.
Northern England - detail & sources
Planting window shifted about two weeks later than southern England. Honest caveat: this crop is a genuinely marginal choice here -- Cultivariable's own harvest timeline (mid-November for a half crop, full maturity not until December/January) assumes a long, mild, frost-free autumn that Northern England often cannot guarantee.
Scotland - detail & sources
Planting window shifted about three weeks later than southern England. Honest caveat: Scotland's shorter, cooler growing season and earlier hard frosts make ulluco a genuinely difficult crop to bring to worthwhile harvest outdoors -- best reserved for the mildest coastal gardens, or grown with season-extension in mind.
Thrives even in poor soil (Cultivariable); loose, light soil is an advantage at harvest time; moderately acidic preferred; compost outperforms synthetic fertiliser.
Lifecycle
Tender tuberous perennial grown as an annual. Cultivariable: best suited to USDA zone 9a and cool maritime climates; performs poorly above 80F (27C), with even brief hot spells cutting yield.
Cultivariable: plant whole or cut seed tubers (with at least two eyes) once frost danger has passed, at a depth equal to the tuber's diameter; space plants about 15in apart in rows 24-36in apart. Plant roughly seven months before the expected first autumn frost to allow enough time to mature.
Canopy establishment
3
Cultivariable: plants form a dense, sprawling ground cover to about 3ft (91cm) across and 15in (38cm) tall, effectively suppressing weeds once established. Full sun gives the best tuber production, though afternoon shade helps where summers run hot -- growth stalls badly above 80F (27C).
Tuber initiation (short-day trigger)
5
Cultivariable: the main tuber-forming trigger only switches on once day length drops to around 13 hours or less, typically after the autumn equinox -- an honestly late and weather-dependent stage in a UK growing year, the same short-day tension already documented for Oca.
Tuber bulking and harvest
8
Cultivariable: tubers keep bulking through November into December/January; earliest worthwhile harvest is mid-November, with full maturity not reached until late December or January. Tubers tolerate a freeze better than the foliage does (about 75% viability after 25F/-4C), so a mild, frost-free autumn is what actually decides the size of the crop.
When to pick: Cultivariable: earliest worthwhile harvest is mid-November (around 50% of potential yield); mid-December approaches 80%; full maturity is reached in late December or January, when most varieties have formed over 100 tubers per plant, though often only around a third are of a marketable size.
Storage
Cultivariable: store at 34-38F (1-3C), 90% humidity, in the dark -- ulluco has been known to keep for up to two years under these conditions, with one year readily achievable.
Cultivariable: Potato leafroll virus is one of the most common viruses found in heirloom ulluco stock.
Papaya mosaic virus disease
Papaya mosaic virus
Cultivariable: Papaya mosaic virus is one of the most common viruses found in heirloom ulluco stock -- over 90% of heirloom varieties carry some virus; seed-grown stock tests clean.
Verticillium wilt
Verticillium dahliae
Cultivariable: Verticillium wilt is the most serious fungal threat to ulluco, with symptoms worsening above 75F/24C.
Ulluco mosaic virus disease
Ulluco mosaic virus
Cultivariable: an Ulluco mosaic virus is one of the most common viruses found in heirloom ulluco stock.
Black scurf and stem canker
Rhizoctonia solani
Cultivariable: Rhizoctonia solani reduces ulluco yields and increases storage losses -- the same soil-borne pathogen behind potato black scurf.
Cultivariable: true seed is extremely rare under natural conditions -- around 1 in 400 hand-pollinations succeeds -- so ulluco is grown almost entirely from seed tubers instead.
Ulluco goes by several regional names across the Andes -- papalisa in Bolivia, olluco in Peru -- reflecting its long history as a staple alongside potato.
Climate: cool maritime best (e.g. coastal strip Vancouver BC to San Francisco CA); USDA zone 9a; performs poorly above 80F/27C, brief heat cuts yield significantly. Tolerates mild frosts; tubers ~75% viable after a 25F/-4C freeze (hardier than potato tubers). Soil: thrives even in poor soil, moderately acidic preferred, loose/light soil helps at harvest; compost/earthworm castings outperform synthetic fertiliser or goat manure. Sun: full sun for good tuber production, afternoon shade helpful in heat. Planting: whole or cut tubers with 2+ eyes, planted after frost danger passes, depth = tuber diameter, 15in between plants in-row, 24-36in between rows, plant ~7 months before expected first frost. Day-length: primary tuberization on underground stolons is day-length-independent; secondary tuberization needs day length down to 13 hours or less (12 or less in most varieties), typically starting after the autumn equinox -- harvest not worthwhile before mid-November. Size: plants ~3ft (91cm) diameter, ~15in (38cm) tall before sprawling; can form 100+ tubers per plant, but often half or more are too small to eat. Propagation: primarily seed tubers; true seed extremely rare (about 1 in 400 hand-pollinations succeeds); stem cuttings root easily in water/moist soil. Storage: 34-38F/1-3C, 90% humidity, darkness -- up to two years, one year readily achievable. Pests: slugs (young plants), field mice and voles (sever stems at ground level), cucumber beetles (serious in some regions); deer show no interest. Diseases: over 90% of heirloom varieties carry viruses -- Papaya mosaic virus, Potato leafroll virus and an Ulluco mosaic virus are most common (seed-grown stock tests clean); Verticillium wilt is the most serious fungal threat, worse above 75F; Rhizoctonia solani also reduces yield and increases storage losses. Harvest: earliest worthwhile harvest mid-November (~50% of potential yield), mid-December approaches 80%, full maturity late December/January. Edible use: tubers raw or cooked (cooking reduces sliminess), flavour earthy/beet-like to mild depending on variety, firm texture; leaves edible raw or cooked, spinach-like.
Ulluco: "easy to grow, frost resistant, and is moderately drought resistant, although the plant prefers soils that are rich in organic matter." Tubers come in a variety of colors and shapes; high water content makes them most suitable for boiling; soft shiny skins need no peeling. Leaves also edible, "rich in protein, calcium, and carotene," similar in texture to spinach -- "a spoonful of cooked leaves can produce a considerable part of a child's daily essential nutrient requirement." Described as the most widely recognized and commercially viable of the Andean root and tuber crops. No specific pest, disease, propagation, size or harvest-timing detail given on this page. Used as a tier-1 substitute for RHS, whose Ullucus tuberosus and named-cultivar pages carry no cultivation content at all.
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.
Frequently Asked Questions
When should I sow ullucos in the UK?
In Southern England, from early May. In Scotland, wait until late May. Treat these as a guide rather than a fixed date — the governing rule is to sow only once frost risk has passed and temperatures are reliably warm enough.
When do I sow ullucos?
Sow early May to late June.
What problems affect ullucos?
Our data links 5 diseases and 4 pests to this crop. See the sections above for each one and how to manage it.
Plan next season before the problems start
Most of the advice on this page comes down to timing and spacing — sowing at the right moment, rotating beds, and giving plants enough airflow. The UK Garden Planner lays your plot out month by month so those decisions are already made before the season starts.
UK vegetable growing guides · Checked against RHS & Met Office guidance
Every SoilCommander guide is written and maintained by our editorial team for real UK growing conditions, and reviewed against Royal Horticultural Society growing advice and Met Office climate data before publication.
Sketch your exact plot shape, pick your UK crops, and get a spacing-accurate bed layout with companion pairings, a rotation plan and month-by-month sowing dates — every fact sourced from RHS and Garden Organic.
