Delphinium Description and Cultural Information
Delphiniums are tall, stately plants with showy flowers on open, branching spikes. Each flower has 5 petal-like sepals with 2 or 4 true petals in the center called a bee. Although we think of these as blue and purple plants, Delphinium species include all three primary colors, blue, red, and yellow. Plants may be short-lived, especially if they are grown in hot, dry conditions. Staking is often required to keep the large flower spikes from breaking in the wind. Keep them well watered and highly fertilized for best flowering and growth.
Delphinium elatum, candle larkspur. 5 - 6'. This extremely tall species has been used extensively in hybridizing. It has blue flowers in summer and is reported to be very cold hardy. Zones 2 - 7.
Delphinium grandiflorum, Chinese delphinium. 1 - 2'. This compact delphinium has deeply divided, dark green leaves and deep blue flowers on airy, open spikes. Different seed strains have flowers in varying shades of blue, white, and light pink and they have a tendency to self-sow rather easily. Zones 4 - 8.
Delphinium nudicaule, Canon delphinium. 1 - 2'. This dwarf delphinium has very interesting orange-red flowers with long spurs. Plants may go dormant after flowering and are often short-lived. Zones 5 - 7.
Delphinium semibarbatum, sulfur delphinium. 1 - 2'. This plant is included simply to represent the different species. It is reported to be difficult to grow, and actually prefers perfect drainage and warm temperatures, the opposite of most delphiniums. It has pale yellow flowers in the summer on wind-resistance stems. Many of its characteristics could help towards developing sturdier, more heat tolerant hybrids. Zones 7 - 9.
Delphinium x belladonna, belladonna delphinium. 3 - 4'. This group has been hybridized for over a century, resulting in smaller but longer blooming plants. 'Bellamosum' is a multi-branching plant with deep blue flowers. Other named hybrids exist in white, sky blue, royal blue, and navy blue. Zones 3 to 7.
Delphinium x elatum, large-flowered hybrids. 4 - 8'. This group of hybrids come in double and single flowers in shades of white, yellow, pink, blue, and purple. They often need staking to prevent them from breaking in the wind and the rain. Zones 2 to 8.
Delphinium x 'Magic Fountain Hybrids'. 2 - 3'. These compact x elatum hybrids come in white, pink, blue, and lavender. Zones 2 to 7.
Delphinium x 'Pacific Giant Hybrids'. 4 - 5'. These hybrids have huge flowers in many colors. Zones 3 - 8.
There are many other hybrids as well. Selecting named plants will give you the best color selection, otherwise purchase plants while in bloom to be assured you get the colors you want.
How to Grow: Delphiniums are very cold hardy and prefer long, cold winters with lots of snow cover. Plants may be short-lived and are often treated as annuals, though, especially in warmer zones. Plant them in moist, humus-rich soil in full sun to part shade. Water and feed throughout the growing season, treating them more like annuals than perennials which usually don't care for so much fertilizer. Remove spent flower stalks and old shoots to encourage reblooming and keep the plants more compact. Divide in spring, if needed, and replant into new soil prepared with generous amounts of compost, although propagation is best done by seed.
Landscape uses: Plant Delphiniums in the cottage garden as a tall, vertical accent. Combine them with lilies, poppies, iris, peonies, daylilies, and many other plants. Plant the taller varieties with other tall plants such as lavender mist meadow rue (Thalictrum rochebrunianum), roses, shrubs, or ornamental grasses. Use the shorter species and hybrids at the middle or front of the perennial border.