Delphinium glaucum aka Sierra Larkspur

Delphinium glaucum is a perennial in the buttercup family, Ranunculaceae. Its common names include giant larkspur and Sierra larkspur. It comes from western North America, from Alaska into the western United States. Its range also includes Yukon, Alberta, and British Columbia. Plants For A Future lists Washington, Oregon, California, and Nevada. It is not native to Britain or Ireland.

This plant grows to about 6 feet [1.8 metres] tall. It flowers from July to August. Each flower has both male and female organs. The species varies enough to cause debate over its boundaries. Some botanists split it into several closely related species. Plants For A Future notes that these divisions lack clear, consistent traits. This makes the names of some plants hard to settle.

Wild plants grow in meadows and along streambanks. They also occur in wet thickets, bogs, and open conifer woods. Their habitats extend from sea level into alpine areas. The upper limit reaches about 10,500 feet [3,200 metres]. Despite these varied settings, garden plants need an open, sunny site. Give them rich, moist soil that drains well. They dislike waterlogged ground and cannot grow in shade. Sandy, loamy, and clay soils can all suit them. They accept mildly acid, neutral, and mildly alkaline soil. Plants For A Future reports hardiness to about −20°C.

Cultivated beds provide a place for this tall perennial. Seed, basal cuttings, and division offer ways to raise more plants. Sow seed in a cold frame in March or April. Outdoor sowing can follow in May. Keep the seed moist and shaded until it sprouts. At 15°C, germination may take two to nine weeks. Higher temperatures can prevent germination. Seed loses viability, so cool, sealed storage matters. Move seedlings into separate pots once large enough to handle. Plant them out in summer. Divide plants in spring or early autumn.

All parts are poisonous, with young plants posing the greatest hazard. No edible uses are known. Plants For A Future gives no medicinal uses. It records a leaf preparation used to kill parasites. That preparation is itself toxic and was for external use only. The same source does not flag the species as weedy.