How to Grow Pearl Lupins UK | Regional Planting Calendar

Pearl Lupin (Lupinus mutabilis)

A pearl lupin plant with pink flower spikes — “Planta de tarwi” by Morales Cynthia is licensed under CC BY-SA 4.0. Source: Wikimedia Commons

2 sources cited · Verified

The short answer

Plant
Mid March to mid May
Ready in
150–330 days
Site
6+ hours of sun, soil pH 4.5–7

In the UK, pearl lupins go in the ground mid March to mid May, and are ready to harvest 150–330 days after planting.

Pearl lupins (Lupinus mutabilis) — Annual, occasionally grown as an short-lived plant taking 2-5 years to reach full maturity in UK conditions.

Timing is the decision that matters most in the UK: sowing mid March, and that same window applies across all 4 regions covered here.

Core growing advice on this page is checked against named horticultural sources — see References.

Regional Planting Calendar

Region Sow
Southern England derived mid March to mid May
Midlands derived mid March to mid May
Northern England derived mid March to mid May
Scotland derived mid March to mid May

Rows marked derived are interpolated between regions our sources do state, because no source we consulted gives a figure for that region specifically. They are deliberately wider to reflect that uncertainty.

Southern England - detail & sources

RHS gives UK-relevant hardiness (H3, tolerant to about -5C) and soil/site detail but no explicit sowing month. Useful Tropical Plants confirms mature plants survive light frost near -5C though heavy/prolonged frost kills them. This mid-March to mid-May direct-sowing window is derived from those two facts, applied as one UK-wide window across all four sub-regions -- a later, more cautious start than a fully hardy crop but earlier than the strictly frost-tender tropicals in this catalogue, reflecting this crop's genuinely better (though still limited) cold tolerance.

Midlands - detail & sources

RHS gives UK-relevant hardiness (H3, tolerant to about -5C) and soil/site detail but no explicit sowing month. Useful Tropical Plants confirms mature plants survive light frost near -5C though heavy/prolonged frost kills them. This mid-March to mid-May direct-sowing window is derived from those two facts, applied as one UK-wide window across all four sub-regions -- a later, more cautious start than a fully hardy crop but earlier than the strictly frost-tender tropicals in this catalogue, reflecting this crop's genuinely better (though still limited) cold tolerance.

Northern England - detail & sources

RHS gives UK-relevant hardiness (H3, tolerant to about -5C) and soil/site detail but no explicit sowing month. Useful Tropical Plants confirms mature plants survive light frost near -5C though heavy/prolonged frost kills them. This mid-March to mid-May direct-sowing window is derived from those two facts, applied as one UK-wide window across all four sub-regions -- a later, more cautious start than a fully hardy crop but earlier than the strictly frost-tender tropicals in this catalogue, reflecting this crop's genuinely better (though still limited) cold tolerance.

Scotland - detail & sources

RHS gives UK-relevant hardiness (H3, tolerant to about -5C) and soil/site detail but no explicit sowing month. Useful Tropical Plants confirms mature plants survive light frost near -5C though heavy/prolonged frost kills them. This mid-March to mid-May direct-sowing window is derived from those two facts, applied as one UK-wide window across all four sub-regions -- a later, more cautious start than a fully hardy crop but earlier than the strictly frost-tender tropicals in this catalogue, reflecting this crop's genuinely better (though still limited) cold tolerance.

Quick Facts

A pearl lupin plant with pink flower spikes — “Planta de tarwi” by Morales Cynthia is licensed under CC BY-SA 4.0. Source: Wikimedia Commons
“Planta de tarwi” by Morales Cynthia is licensed under CC BY-SA 4.0. Source: Wikimedia Commons.
Factor Value
Soil pH 4.5 - 7
Sunlight 6-8 hours direct sun
Optimal growing temp 18-24C
Minimum survivable temp -5C
Time to harvest 150-330 days
Soil texture Loam, sand (RHS); succeeds in any moderately good soil (Useful Tropical Plants)
Drainage Moist but well-drained (RHS); well-drained soils preferred, though it succeeds on poor soils via its deep taproot (Useful Tropical Plants)
Lifecycle Annual, occasionally grown as an short-lived plant taking 2-5 years to reach full maturity in UK conditions (RHS); Useful Tropical Plants records it as an annual 50-250cm tall that continues flowering and seeding until frost kills it, taking 5-11 months to fully ripen its crop.
Edible parts seeds

At a Glance

Close-up of a white, pink and yellow pearl lupin flower — “Lupinus mutabilis en el humedal El Burro” by Juan Carlos Sáenz Rodríguez is licensed under CC BY-SA 4.0. Source: Wikimedia Commons
“Lupinus mutabilis en el humedal El Burro” by Juan Carlos Sáenz Rodríguez is licensed under CC BY-SA 4.0. Source: Wikimedia Commons.
Lupinus mutabilis Pearl Lupin Lupin aphid Slugs PESTS

Soil & Growing Conditions

A field of flowering pearl lupin plants — “Lupinus mutabilis Cotacachi” by Awkiku is licensed under CC BY-SA 3.0. Source: Wikimedia Commons
“Lupinus mutabilis Cotacachi” by Awkiku is licensed under CC BY-SA 3.0. Source: Wikimedia Commons.

Water: Prefers 500-1000mm annual rainfall, tolerates a range of 350-1700mm (Useful Tropical Plants)

Soil pH range

4.5 7

Span reflects genuine variation between the cited authorities, not a single agreed figure.

Growth Stages

A pearl lupin palmate leaf with dew drops — “Hojas de tarwi” by AsiriMH is licensed under CC BY-SA 4.0. Source: Wikimedia Commons
“Hojas de tarwi” by AsiriMH is licensed under CC BY-SA 4.0. Source: Wikimedia Commons.
Stage BBCH Notes
Sowing and establishment 0 Pre-soak seed 24 hours in warm water before sowing in situ; protect from mice. Germination takes place within about 2 weeks (Useful Tropical Plants). RHS grows the crop from seed, propagated indoors or outdoors.
Vegetative growth 3 Erect, bushy growth to 0.5-1m in UK cultivation (RHS), though up to 2.5m recorded in its native range (Useful Tropical Plants); blue-green leaves of 7-9 leaflets. The deep taproot breaks up poor subsoil, and as a nitrogen-fixing legume the crop can fix up to 400kg N/hectare (Useful Tropical Plants).
Flowering 6 Upright spires of small, pea-like flowers on blue-green foliage (RHS). Flowering and pod-set continue until frost kills the plant (Useful Tropical Plants).
Fruiting and harvest 8 Takes 5-11 months in total to fully ripen its seed crop; the continuous flowering habit makes mechanical harvesting difficult (Useful Tropical Plants). Recorded seed yields range from 290kg up to 7 tonnes per hectare depending on region and variety.

Harvest & Storage

Harvested pearl lupin (tarwi) seeds at a market — “Mercado Punata - Cochabamba Bolivia - Mercado Central de Punata 22 - Tarwi - chuchusmuti” by Mauri777AE is licensed under CC BY-SA 4.0. Source: Wikimedia Commons
“Mercado Punata - Cochabamba Bolivia - Mercado Central de Punata 22 - Tarwi - chuchusmuti” by Mauri777AE is licensed under CC BY-SA 4.0. Source: Wikimedia Commons.

When to pick: Continuous flowering and pod-set until frost kills the plant makes mechanical harvesting difficult; the crop takes 5-11 months in total to fully ripen (Useful Tropical Plants). Seed yields recorded from 290kg up to 7 tonnes per hectare depending on region and variety, with an oil content up to 18%.

Storage

Raw seed is toxic and must be processed before eating: soak overnight, or 2-3 days with water changes, to leach out bitter quinolizidine alkaloids; some low-alkaloid "sweet" forms bred for lower toxicity need less processing (Useful Tropical Plants). RHS confirms the plant is harmful if eaten unprepared, including to pets.

Pests

A blue, white and yellow pearl lupin flower spike — “Flor de Tarwi” by Cggtcggt is licensed under CC BY-SA 4.0. Source: Wikimedia Commons
“Flor de Tarwi” by Cggtcggt is licensed under CC BY-SA 4.0. Source: Wikimedia Commons.
Lupin aphid
moderate

Macrosiphum albifrons

Named directly by RHS as one of the main pests of lupins; RHS's dedicated advice page states severely impacted plants typically wilt.

Slugs
low

Gastropoda (slugs, various spp.)

Named directly on RHS's own growing-guide page as one of two pests this crop is susceptible to (no severity grading given).

References

  1. Annual/biennial, erect bushy habit, blue-green 7-9 leaflet leaves, upright spires of small pea-like flowers. Hardiness H3 (-5 to 1C). Soil: loam/sand, moist but well-drained, acid/neutral. Full sun/partial shade. Height 0.5-1m, spread 0.1-0.5m, 2-5yr to maturity. Grown from seed. Pests: slugs, lupin aphid. Diseases: powdery mildews, rots, leaf spot, plant viruses. Seeds edible once processed; toxic/harmful to pets if eaten unprepared. Family Fabaceae, not native to GB/Ireland. Also known as tarhui/tarwi.

  2. Annual 50-250cm, 5-11 months to fully ripen crop, flowers/seeds continuously until frost kills plant. Optimal temp 18-24C, tolerates 6-30C; mature plants survive to about -5C but heavy/prolonged frost kills. Elevation to 4000m in tropics. Rainfall 500-1000mm (tolerates 350-1700mm). Soil: any moderately good soil, pH 5-6.5 preferred (tolerates 4.5-7), acid/neutral, intolerant of lime, well-drained, succeeds on poor soils via deep taproot. Sunny position. Propagation: pre-soak seed 24hr, sow in situ, protect from mice, germinates within 2 weeks. Seed yield 290kg-7 tonnes/hectare, oil content to 18%. No specific pests/diseases documented by this source. Edible: cooked seeds only -- bitter toxic alkaloids in many forms, leached by soaking overnight or 2-3 days with water changes; some low-alkaloid sweet forms exist. Up to 50% protein. Nitrogen-fixing green manure, fixes up to 400kg N/hectare. Also used for edible oil, ornamentally, and cooking water as a pesticide.

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 pearl lupins in the UK?

In Southern England, from mid March. In Scotland, wait until mid March. 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 pearl lupins?

Sow mid March to mid May.

How long do pearl lupins take to grow?

Typically 150–330 days, depending on cultivar and growing conditions.

What soil pH do pearl lupins need?

A pH of about 4.5–7. That span reflects genuine variation between the authorities we cite rather than a single agreed figure — the References section lists each source's exact range.

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.

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Last verified 2026-09-03