Lupins are a cool-climate legume with a bold, typically purple, flower, though white, pinks, reds and yellows are also found. The yellow bean the plant produces, called a lupin bean, is traditionally harvested and pickled in salt water. As an ornamental, lupins make a striking addition to a vegetable or flower garden. Lupins have nitrogen-fixing properties that are typical of the legume family.
Plant your lupins a cool area that gets partial sun. Avoid full sun and very hot climates. U.S. Department of Agriculture Plant Hardiness Zones 4 to 9 are ideal for growing this flowering legume. Generally, if daytime temperatures reach a consistent high of 90 degrees F or above, it is not the right climate for a lupine crop.
Lupins like loose sandy, loamy soil best but this hardy plant can adapt and succeed in wet, heavy soil and soil that has been depleted of nutrients. Being a nitrogen-fixing legume, lupins can be planted as a cover crop to rehabilitate poor gardens or fields.
To get a head start on the season, start lupins indoors eight weeks before the last typical frost date. Soak the seeds in warm water for 24 hours prior to planting and then bury each seed 1/8 inch deep in planting trays filled with peat moss. Keep the trays in a cool place were temperatures remain between 55 and 65 degrees.
When the last frost has passed, transplant your lupin seedlings outdoors 12 inches apart. You can plant lupins in rows that are 12 inches apart when planting as a field crop. Or, plant your lupin seedlings in a flower or vegetable garden to attract pollinators and improve the soil. If you are planting seeds directly into the soil, plant each seed 1 to 2 inches deep.
Fertilizers should not be necessary, but if you do decide to fertilize your crop avoid nitrogen fertilizers. Because lupins absorb nitrogen from the atmosphere, adding additional nitrogen to the soil can overload and stress the plants.
Keep the soil around your lupins consistently moist to a depth of at least 3 inches; you can check the moisture in the soil with your index finger. Water more in hot, dry weather and less in wet, rainy weather.