Lupinus arboreus aka Bush Lupine

Lupinus arboreus belongs to the pea family. Its names include tree lupin and yellow bush lupine. It is native to western and southwestern California. Its range reaches south to northern Baja California. It grows near coasts in stable dunes, scrub, and pine woods. It now grows wild by the sea in southern England, too. This woody shrub grows fast and can shelter less hardy plants.

Garden plants reach about 5–8 feet [1.5–2.5 metres] tall and wide. In open ground, they can form a rounded bush. The bark is grey. Young stems are green to reddish-green. The grey-green leaves are palmate: five to eleven leaflets spread like fingers. Fine, silky hairs coat the lower side of each leaf. RHS says the leaves stay on all year. Virginia Tech calls them deciduous, meaning they fall each year. These views leave year-round leaf cover less sure across growing conditions.

Scented flowers rise above the leaves in late spring and summer. Most are yellow. Sources also note blue or purple blooms. The upright flower spikes, called racemes, reach about 1 foot [0.3 metres] long. Brown hairs coat the seed pods, which look like pea pods. Each pod is about 1.5–2.5 inches long. Ripe pods split with force. They twist apart and throw out seeds. The flowers suit cutting for use indoors.

Full sun gives the best growth, though the shrub copes with part shade. Use sandy or loamy soil that drains well. The soil should be acidic or neutral. Sources give moisture needs from dry to moist. Mild gardens near the coast suit it, even in sea winds. In colder places, shelter helps guard against long, hard frosts. RHS rates it H4. Plants For A Future lists USDA zones 7–10. Plants reach full size in two to five years. They need little routine pruning. Grow them from seed or basal cuttings, taken at the base.

Use it in informal beds, borders, or coastal planting. Its roots help hold loose sand. The plant also adds nitrogen to soil. Flowers give yellow dye, and root fibres have supplied string. It can become weedy, so watch its local spread. Slugs and lupin aphids may attack it. Problems also include powdery mildew, rots, leaf spot, and viruses. The supplied evidence lists no edible or medicinal uses. RHS warns that eating it harms people and pets. RHS also says to wear gloves and protective clothing when handling plants.