How to Grow Pearl Lupins

At a Glance

Quick Facts

Factor	Value
Soil pH	5 - 6.5
Optimal growing temp	18-24°C
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)
Edible parts	seeds

Soil & Growing Conditions

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

Soil pH range

5 6.5

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

Growth Stages

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

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

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).

Sources

1. Useful Temperate Plants - Lupinus mutabilis

   Mirrors FAO Ecocrop. Fetched and parsed directly for the numeric soil pH range.

2. Useful Tropical Plants Database (Ken Fern) - Lupinus mutabilis

   Annual 50-250cm, 5-11 months to fully ripen crop, flowers/seeds continuously until frost kills plant. Optimal temp 18-24°C, tolerates 6-30°C; mature plants survive to about -5°C 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.

These 2 sources are specific to this region. The full list of 3 sources behind this guide (Royal Horticultural Society, Useful Temperate Plants, Useful Tropical Plants Database (Ken Fern)) is in the references of our UK guide to pearl lupins; they describe the plant itself, which is the same wherever it grows.