Perennial lupin (Lupinus perennis), also called wild or sundial lupin, is a perennial flowering plant native to disturbed sites, open woodlands and sandy hills in the eastern and central United States and Canada. Lupins work well in naturalistic plantings, in floral arrangements or as ornamental roadside flowers. They also make attractive and important additions to butterfly gardens.
Perennial lupins usually grow around 4 feet tall. They have palmately compound leaves, or leaves shaped like the palm of a hand. Each individual leaf is composed of seven to 11 leaflets that grow around a single point on the leaf stem. In the spring, elongated clusters of pink, blue or white blossoms appear at the ends of the slightly hairy flowering stems. Flattened, oblong, hairy pods follow the blossoms. Each pod carries several large, hard seeds.
Perennial lupin plants benefit the soil by transforming nitrogen from the environment into a form that is useful to plants, which enhances the fertility of the soil. This species is also the primary larval host and food source for the Karner blue butterfly, an endangered butterfly species from the Great Lakes region. Female adults lay their eggs near sundial lupins. The caterpillars feed on the leaves, while the adults feed on the nectar. Since they do not feed on any other species but lupin, this limits the areas where Karner blue butterflies can live. Frosted elfin butterflies are also dependent upon lupins for survival.
Sundial lupins are cold-hardy in United States Department of Agriculture hardiness zones 3 through 9. They require full sunlight and grow best in well-drained, sandy loose soil. This species generally cannot adapt to heavy soil. They reproduce through seeds or rhizomes, which are thick underground stems; new plants form each year in the same location. Lupin seeds germinate 15 and 75 days after planting. Plants do not usually start blooming until their second year.
Rub lupin seeds with sandpaper and soak them overnight in room-temperature water to loosen the seed coat. Plant them approximately a quarter of an inch deep in small pots or trays. The seeds do not germinate easily, according to the United States Department of Agriculture Forest Service, and many seedlings do not survive. They are susceptible to root rot infections when grown in containers, so transfer the young plants outdoors as soon as they have two or three leaves. Older plants do not tolerate having their roots disturbed and will die if uprooted or transplanted.