Lupinus diffusus aka Sky Blue Lupine

Lupinus diffusus has two common names: skyblue lupine and blue sandhill lupine. This wildflower is part of the bean family, Fabaceae. It comes from the southeastern United States. Its range spans North Carolina to Florida and west to Mississippi. It grows in scrub, sandhills, coastal strands, and pine flatwoods. In North Carolina, it grows in the south near the coast.

The plant grows upright and spreads out at a moderate rate. It reaches 1.5–3 feet (0.46–0.91 metres) tall. It spreads 2–3 feet (0.61–0.91 metres) wide. Sources call it a perennial, though it can also be biennial. Its green leaves stay on the plant year-round. Fine white hairs make the leaves feel soft. The detailed leaf account says each oval leaf is undivided. Each has smooth edges and measures about 0.33 feet (0.10 metres) long. Leaves grow in turn along the plant or in rosettes. The stems have no scent.

Blue flowers bloom from March through May. Each pea-like bloom has a white mark on its upper petal. The two lower petals join together. Dense racemes, or flower clusters, rise above the leaves. Long, flat legume pods follow from June through July. The flowers draw bees and have special value for bumblebees. Gray hairstreak butterflies use the plant to host their young. These traits suit gardens for native plants and butterflies. They also suit plantings near the coast. The blue blooms add a garden accent.

Full sun gives this lupine the best bloom. Light shade in the afternoon can help in hot summers. It needs dry, sandy soil that drains well. It grows best in mildly acid soil and withstands drought. NC State lists USDA hardiness zones 4–10. Yet hot, humid summers can shorten its life in zones 7–9. Gardeners there may need to grow it as an annual. Its deep taproot makes rooted plants very hard to move. Seeds may lie dormant for years before they sprout. Growing new plants in pots can be hard, too.

Powdery mildew can harm this lupine. Good airflow helps curb the problem. Its strict root and soil needs make it hard to grow. The seeds hold poisonous alkaloids and are not food. Eating large amounts can make you drowsy. It can also slow the heartbeat and cause trouble breathing. Convulsions may occur, too. NC State rates its poison severity as low. The plant does not cause contact dermatitis, a skin rash from touch.