Not everyone will have positive memories of collecting wild, blooming lupines from vacant lots and fields. They were so lovely and made a great (and inexpensive) table decoration for a poor college student.
The purple (with a bit of white) lupines are more common in the norther part of the lupine range. Southward in California and Baja California, one would find soft yellow blooms.
Lupines are fairly invasive throughout much of its range and in areas where it has been introduced (like western Europe, Australia, New Zealand, South America, and more). So why was it introduced?
Spreading this plant around was more than ‘it seemed like a good idea.’ Finding a way to add nitrogen to a site with poor soils can be a challenge. Lupines are able to fix (collect/create) in the soil.
On the other hand, species on nitrogen-poor soils have probably adapted. Adding back non-native nitrogen will gradually change soil chemistry, allowing other invasives to establish, and push out or weaken native plants.
Tree lupine will hybridize with other native lupines which can endanger the natives. There are approximately 220 species of lupines with many growing in the North American west.
The Plants for a Future website described Lupine as the “Right Plant Wrong Place” meaning it may or may not be invasive in your region.
This perennial plant can live up to seven years. This plant is a strong grower and can outcompete other grasses, forbs, and native plants.
They will grow in a number of different soils including sand dunes and coastal sage scrub. This plant has been, the past, used to help stabilize sand dunes and other soils. Good draining soil is a must.
Most lupines require full sun. Unlike the northern purple blooming type, the yellow southern variety will grow to six feet in the sun. The northern varieties seem to be significantly shorter.
It doesn’t hurt that the plant can have pretty blooms. The fragrant, soft yellow, pea-like bloom can be 12 inches long. The flowers are rich in nectar and pollen.
Leaf color can vary per variety. The leaves for the yellow bloomers are grey-green where the purple bloomers are more dark green.
In all cases, the leaves are ‘palm’-shaped (palmate) with 5-12 leaflets each. Leaflets are often covered with fine silky hair.
This plant creates a lot of seeds every year. The seeds are relatively large and can survive for a very long time.
Like other plants (think Scotch Broom and Gorse), the seeds from the yellow lupine will build up in the soil. This seed bank makes the plant very difficult to remove once it is established.
Unsprouted seeds rest in a seed bank below the shrub in a shallow mat. Seeds often sprout with a disturbance (such as manmade or environmental). Seeds can be spread by rodents, wind, water, disruptions, etc.
The plant is not only attractive to humans, but it also attractive to many bees, butterflies, and moths. It plays host to 10 butterflies and moths, and potentially 39 in total. Lupines do not appear to be attractive to birds.
A variety of lupins are available commercially through nurseries.
Several varieties of Lupine can be toxic; others are not. Some parts of the plant (the seeds for instance) may be more toxic than others, and the season can also be a factor in toxicity level.
The consensus seems to be that the plant can be toxic to cats, dogs, sheep, and people. Livestock (except sheep) seem to be unaffected.
So perhaps making bouquets with this plant is not such a bad idea. One could minimize seed build-up by removing the seed. Better yet, make bouquets.
Tips: Put cut flowers into water (they wilt quickly and only last a few days). Do not add the spent bouquet/seeds to the compost pile. Appropriately dispose like other invasive plants in your area/season. As a general practice, wear garden or plastic surgical gloves when working with any plant particularly those that might be toxic.
—The Danger of Lupine (https://homeguides.sfgate.com/)
–US Dept. of Agriculture, Plant Inventory (https://plants.sc.egov.usda.gov/core/profile?symbol=LUPIN)
–Wikipedia, Lupine arboreus (https://en.wikipedia.org/wiki/Lupinus_arboreus)
–Gardeners World, Lupine arboreus (https://www.gardenersworld.com/plants/lupinus-arboreus/)
–Plants for the Future (https://pfaf.org/User/Plant.aspx?LatinName=Lupinus+arboreus)