Lupin

Name: Lupin, lupine, Lupinus Polyphyllus, L. Perennis, L. Arboreous.

Height: Usually 0.6 to 2m.

Foliage: Green dissected compound leaves, arranged radially rising from herbaceous stems.

Climate: Prefers dry summers and cool, wet winters.

Soil: Prefers well-drained, moderately fertile sandy soil.

Position: Full sun to partial shade in warmer temperate climates.

Flowering and fruiting: Colourful vertical spikes of single-coloured or two-toned pea-like flowers from spring to early summer, developing into flat, hairy, pea-like pods that split open when mature, shedding the hard seeds.

Feeding: Use a controlled release organic fertilizer specifically for flowering plants in early spring. Avoid fertilizers high in nitrogen as lupins have nitrogen-fixing roots.

Watering: Regular watering throughout the spring and summer growth periods.

Characteristics of Lupins

Lupins form mounding upright clumps of fresh green foliage, dissected into leaflets like the spokes of a wheel. Upright spikes of dramatic flowers in singular or two-tone colour combinations arise from the domes of foliage in spring and early summer. These colours include shades of blue, purple, pink, yellow, red, orange and white. There are dwarf cultivars from 0.6 metres high to tall varieties up to 3 metres. The most famous are the Russell lupins, although many species and cultivars are grown as green manure crops, to provide fodder for animals, or for human food production including flour.

Climate 

Lupins will grow in most temperate climates with dry summers and cool, moist winters. They prefer to be planted in full sun or partially shaded environments in hot climates. Lupins usually die back to the ground in autumn before reshooting the following spring. They can be used in cottage gardens and borders to provide pops of early summer colour or mass planted for a dramatic impact. 

Soil

Lupins grow best in free draining soils with a pH around 6.5–7. They can survive in relatively poor soils due to their nitrogen-fixing roots. Adequate moisture in their growth phase from spring to early summer is essential for healthy growth. Winter wet conditions may cause root rot.

On farms, lupins are often planted by seed, grown to maturity and then turned into the soil, before planting with other vegetable or grain crops, as their nitrogen-fixing roots improve nutrient-deficient soils. This is often called a ‘green manure’ crop.

Pruning lupins

Remove fading flowers promptly before the hairy pods swell, to prevent the plant from going to seed and reducing its vigour. 

This will encourage a second flush of flowers later in summer, although these will be smaller than the first spikes. 

In autumn or after the first frost, cut the stems back down to the ground.