What’s that soft yellow bush in the distance? It just might be a Tree Lupine (Lupinus arboreus). The common names are yellow bush lupine (US) or tree lupin (UK).
This perennial will grow to about 79-inches in full sun. Tree lupins typically live up to seven years and are hardy to 10˚F.
The attractive yellow flowers held on a 12-inch stem is rich in nectar and pollen. The gray-green leaves are palm-shaped and covered with fine, silky hair.
Lupins are attractive to many bees, butterflies, and moths. Tree Lupins host to ten or more butterflies and moths. Some have estimated the number to be upwards of 39 in total. Lupines do not appear to be attractive to birds.
The term lupine is from the Latin for “wolf,” referring to the mistaken belief that these plants deplete soil minerals. The opposite is actually true.
Many species of Lupine will collect nitrogen from the air. This ability gradually enriches surrounding soils and may displace native varieties adapted to more nitrogen-poor conditions.
Tree lupins are strong growers and can outcompete other grasses, forbs, and native plants. It grows in a number of different soils with good drainage including sand dunes and coastal sage scrub. At one time, this plant was used to stabilize sand dunes and other soils along the Oregon and California coast.
This species can threaten native plants through hybridization. There are approximately 220 species of lupines with many growing in the North American west.
Yellow Lupin creates a lot of seeds every year. These seeds persist in the soil for a very long time and can create a seed bank.
Unsprouted seeds collect and lay dormant in a shallow mat below the shrub. This seed bank will sprout with even minimal disturbance. Disturbances can include manmade or environmental. Even something like rodent activity or wind is enough to cause sprouting.
Lupins can be toxic depending on season, variety, and plant parts. Seeds for instance are often very toxic. A wide variety of less invasive and colorful lupines are available commercially.
–Tree Lupine, https://www.fws.gov/refuge/Humboldt_Bay/wildlife_and_habitat/YellowBushLupine.html
—Lupine arboreus, https://calscape.org/Lupinus-arboreus-()