Delphinium

Delphiniums produce the most extraordinary vertical element in the garden: spikes 4 to 6 feet tall packed with flowers in true blue, purple, white and bicolours, often with a contrasting central bee, irresistible to bumblebees and impossible to substitute. They are also among the more demanding plants: rich, deep, moisture-retentive soil, staking before the stems reach full height, shelter from wind, and cool summers. The Pacific Giants are the tall classics; the Magic Fountain and New Millennium strains are shorter and sturdier.

Plant in full sun, 18 to 24 inches apart, in deeply dug soil with compost worked in and a near-neutral pH, and keep them watered, especially in the first year. Set the stakes at planting. Cut the main spike when the lower third of the flowers is open; after the first flush, cut back to the lateral shoots for a second, smaller flush in late summer. Slugs eat the spring shoots, and mildew arrives in a humid August.

With good drainage they are reliably perennial through cold winters, zones 3 to 7, and short-lived where summers are hot. All parts are toxic if eaten, so wear gloves and keep them from grazing animals; deer and rabbits leave them alone for the same reason. They last a week in the vase and the hollow stems can be filled with water and plugged.