Lupin (Lupinus polyphyllus) is a colourful perennial bloomer that produces colourful flowers on upright spikes measuring between 30 cm and 1.2 m (1 and 4 feet) tall. Although lupin is often purple, the plant is also available in blue, yellow, pink or white. For planting in late spring or summer, lupin seeds must be prepared ahead of time. If you prefer to plant lupin seeds in late winter, the seeds require no preparation, as nature will do the job for you.
Collecting lupin seeds
Although you can buy lupin seeds commercially, lupin seeds are often collected from existing plants between June and August. Remove dry pods from the plant, then place the pods in a paper sack to dry. Store the paper sack in a cool, dry spot where the seeds will be out of the reach of rodents. Leave the pods in the sack until planting time. The seeds will be naturally expelled from the pods as the pods dry.
Preparing the seeds
Nick each lupin seed lightly with a sharp knife or a piece of sandpaper, as lupin seeds have a hard coating and won't germinate easily without nicking, or scarifying the seed. If you're planting a large number of lupin seeds, fill a glass jar half full with coarse sand, then place the lupin seeds in the jar. Shake the for several minutes, or until the seeds have all been nicked. Soak the seeds in a bowl of hot water for about three hours. Discard any seeds that float and plant the seeds that sink to the bottom.
Preparing the soil
Prepare the soil in an area in full sunlight or light shade. Use a tiller or a garden fork to work the soil to a depth of 30 to 50 cm (12 to 20 inches). Although lupin will grow in sand or nearly any well-drained soil, the plant won't usually tolerate heavy clay soils.
Planting lupin seeds
To plant lupin seeds, simply scatter the seeds over the prepared soil. Cover the seeds lightly with no more than 6 mm (1/4 inch) of soil, then water the area with a hose and spray attachment to avoid loosening the seeds. Plant prepared seeds any time in spring, or in summer before August first. Preparing the seeds will cause the seeds to swell, much as they would naturally if expelled from the plant and left on the ground. Unprepared seeds must be planted between September and November, as the cold weather will prepare the seeds for germination in spring.