For the back of the perennial border, few plants can rival the dramatic display of delphiniums. Most varieties produce 4- to 6-foot spikes filled with 1-inch, fragrant blooms. Most are blue, but some are white, pink, or purple.
New dwarf hybrids have also been developed that grow to only about 2 feet. Delphiniums bloom in early summer and, if deadheaded after first bloom, again in the fall. The tallest, most spectacular types do best in places with extended cool weather, such as the Pacific Northwest, but shorter ones do well in many other parts of the country. They are next to impossible to growing in hot, dry areas.Notable VarietiesMid-Century Hybrids are resistant to mildew, 4 to 5 feet tall, and are available in many colors.Pacific Giant Hybrids grow 6 feet tall and produce double flowers in a wide spectrum of colors.CareDelphiniums do best in alkaline soil and regions with an extended cool growing season, such as the Pacific Northwest. They need fertile, moist soil in partial shade to full sun. Delphiniums should be fertilized at least once during the growing season. Protect from wind and provide support as flower stalks develop. Deadhead to promote rebloom. They are short-lived plants that may need to be replaced after a few years.PlantingPlant in spring in full sun in alkaline soil rich in organic matter. Ensure that crown is at soil level to avoid rot. Space 12 to 36 inches apart depending on variety. Propagate from seeds sown in spring or midsummer. In areas with cold winters, protect young seedlings by mulching after the soil freezes, or by overwintering in a cold frame. Divide established clumps in early spring (in mild-winter climates, in fall).Pests and DiseasesDelphiniums are susceptible to slugs, snails, mites, and mildew. A regular pest control program is recommended.