Delphinium trolliifolium aka Cow Poison

Delphinium trolliifolium belongs to the buttercup family, Ranunculaceae. This plant lives for more than one year. Its home range runs from Oregon into northwestern California. It grows where the climate is temperate, or mild. Chicago Botanic Garden calls it Columbian larkspur. The RHS gives another name: Californian cow-poison. It is not native to Britain or Ireland. The RHS has yet to resolve its name status.

This larkspur grows upright and bears tall flower spikes. The blooms are dark purple-blue, with a white “bee.” This is the name for the flower's white center. That pale part stands out against the dark parts. Chicago lists white, blue, and purple as bloom colors. These shades appear together in the flower show it describes. The plant blooms from May through June. Its tall spikes give it a clear upright shape. This shape and the flower colors provide its main garden appeal.

Chicago lists full sun and part shade as options. Its care notes put more stress on part shade. They also call for soil rich in humus. This soil must hold moisture through dry spells in summer. The listed need for water is moderate. The plant thus suits sites that stay moist in summer. The soil should not dry out all the way. Chicago lists USDA hardiness zones 6–9 for this plant. It can cope with winter cold in those zones. It still needs soil that holds water in summer.

This plant lives for years, but its life is short. It is not a long-term part of the garden. Chicago says to let seeds ripen and fall in autumn. New plants from seed can help keep it growing there. Suggested uses include beds, borders, and groundcover. It also suits planting beneath taller plants, in part shade. Its upright shape and flower spikes fit the border role. The groundcover use does not mean its form lies flat.

Chicago says the plant draws both birds and butterflies. It also lists the plant as deer resistant. These traits add wildlife interest to its early-summer blooms. Chicago reports few insect or disease problems. This does not mean pests will never cause harm. Shade and soil that holds moisture remain its main care needs. Letting seeds ripen helps offset its short garden life. The supplied species accounts give no clear advice on edible uses. Nor do they give clear guidance on toxicity.