Common Name: Tree Lupin

General Information

Lupinus arboreus is an evergreen shrub usually growing up to 150cm tall, occasionally reaching 300cm and almost as much wide[, ].
The plant is harvested from the wild as a source of materials. It is sometimes grown in reclamation projects and as a soil stabilizer, and is often grown as an ornamental.
Often grown as an ornamental, the plant has often escaped from cultivation and become naturalized in several countries.

Known Hazards

Lupinus species in general (and especially the seeds) contain a range of bitter-tasting alkaloids such as lupine, anagyrine, sparteine and hydroxylupanine. The pharmacological effects of these alkaloids are that they block ganglionic transmission, decrease cardiac contractility and contract uterine smooth muscle[]. When ingested in moderate to large quantities they can cause symptoms such as respiratory depression and slow heartbeat, sleepiness and convulsions[].
Alkaloid levels can vary greatly from species to species, and several members of the genus are used for food. In some species low-alkaloid, sweeter-tasting varieties have been developed. There are also techniques (particularly soaking and discarding the soak water) that lower the alkaloid levels.
Unless it is known that the plant is low in alkaloids then caution should be applied to any ingestion of the plant[].
Fungal toxins can readily invade the crushed seed and can cause chronic illness[].

Botanical References

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Range

South-western N. America - western and central California

Habitat

Stable sand dunes, coastal scrub and pine forest close to the coast. Naturalized by the sea in S. England[].

Properties

Weed Potential	Yes
Other Uses Rating
Habit	Evergreen Shrub
Height	1.50 m
Growth Rate	Fast
Pollinators	Bees, Insects
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Lupinus arboreus is winter hardy to about -15°c[, ]. Plants are hardy in all but severe winters in Britain[], though they become less hardy with age[].
Requires a well-drained dry or moist soil in a sunny position[, ]. Prefers an alkaline soil[]. Grows well near the coast[], resisting maritime exposure. Established plants are drought tolerant[]. Plants can be grown in quite coarse grass, which can be cut annually in the autumn[].
A fast-growing but short-lived plant[], especially when growing in rich soils[]. Plants have reached 2.7 metres tall and wide within 4 years from seed in a rich soil, flowering and producing seed prolifically[].
Plants self-sow when in a suitable position[].
The flowers bear the fragrance of white clover[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

None known

Medicinal

None known

Agroforestry Uses:

Plants are used in land reclamation schemes to stabilize sandy soils and coastal dunes[, ]. They are also used to improve the soil in pine forests[].Because they are fast growing and tolerant of maritime exposure, they quickly provide shelter for other plants as well as enriching the soil with nitrogen[].
An excellent pioneering plant in permaculture, even in exposed areas it grows rapidly to its maximum height of about 1.5 metres and will give shelter to enable other less tolerant plants to become established. It is especially useful for helping the establishment of shrubs and herbaceous perennials in small gardens[].

Other Uses

A bright yellow dye is obtained from the flowers[].

The root fibres have been used to make a string for making nets etc[].

We have no specific information for this species, but the soakwater used to extract alkaloids from several edible species of lupin has been shown to be effective as a biocide[].

Propagation

Pre-soak the seed for 24 hours in warm water and then sow in early spring in a greenhouse[, ]. The seed is best sown in individual pots since the plants strongly resent root disturbance. Germination should take place within a couple of weeks. If sown in trays, then the seedlings should be potted up into individual pots as soon as they are large enough to handle. Plant out in early summer when the plants are around 15cm tall.
It should also be possible to sow the seed in situ in mid to late spring. Protect the seed from mice.
Cuttings of short side-shoots with a heel, mid summer in a frame[].
Basal cuttings, mid spring in a cold frame. Harvest the shoots when they are about 10cm long with plenty of underground stem. Pot them up in a very sandy soil in individual pots and keep them in light shade in a cold frame or greenhouse until they are rooting well. Plant them out in the summer.
Division in early spring. Difficult.
Lupin propagation is usually carried out by seed - vegetative propagation is normally only used when propagating named cultivars[].