Oh, the delightful delphinium! The stalwart of many summer flower gardens, these showy perennials are grown for their long, colorful spikes in blue and other gorgeous hues.
Flowering all summer, delphiniums are butterfly and hummingbird magnets, too! Learn how to plant, grow, and care for delphiniums.
Delphinium is a genus in the Ranunculaceae family. (They’re often confused with larkspur, which are a different plant species.) There are more than 300 delphinium species, so there is quite a variety of heights, from dwarf hybrids to 6-foot tall beauties, so they can be planted in the front, middle, or back of a perennial border. The blue delphinium is most common, but varieties also come in gorgeous shades of violet, pink, white, red, and purple. They are popular in both cottage-style and cutting gardens.
Most delphiniums are short-lived perennials, lasting 2 or 3 years in the garden. Some varieties will bloom throughout the entire summer if the plants are cut back regularly. Other hybrids bloom from early to mid-summer and will produce a second flower display in late summer or early fall if you cut off the old flower stalk.
What’s important to know about delphiniums is that they will thrive if you meet their specific conditions. Delphiniums prefer moist, cool summers; they do not fare well in hot, dry weather or sudden wind or rain, which can knock them down. Most varieties will need staking. See more details below.
Are Delphinium Poisonous?
Yes, delphiniums are highly poisonous. If seeds and seedlings are ingested, they can cause nausea, twitching muscles, paralysis, and even death. This is mainly a concern for grazing animals such as cattle, horses, and sheep, and it is also a caution to gardeners with small children.
Growing
- Delphiniums are heavy feeders. Apply a balanced liquid fertilizer starting in early spring every 2 to 3 weeks.
- Insert sturdy stake supports no later than mid-spring or when the plants reach 12 inches high.
- Do not allow the soil to dry out, but avoid puddling. Water plants during the summer if rainfall is less than 1 inch per week.
- For ideal flower spikes, thin side shoots at 3 inches high, leaving 2 or 3 shoots on young plants and 5 to 7 shoots on mature, well-established ones.
- Deadhead by cutting spent flower spikes back to small, flowering side shoots.
- After delphiniums have finished blooming, cut flower stalks to the ground, and new, though smaller, flower stalks will develop. The flowers will survive the coming cold days and even light frosts. (See local frost dates.)
- Every 3 to 4 years, divide plants in spring: Remove and replant the new little plants growing around the outside of the clump. Discard the hard old heart.
Types
- Belladonna Group: blue flowers native to North America; easier to grow and longer-lived than varieties in the Elatum Group (below); upright, loose, and branching perennials; secondary flower spikes extend bloom period into autumn; 3 to 4 feet tall. ‘Blue Donna’ has clear, blue flowers.
- Elatum Group: tallest varieties in shades of violet, blue, pink, and/or white; short-lived; reach 6 feet tall or more. ‘Aurora Deep Purple’ has purple flowers with a white center.
- Pacific Hybrids: 3-inch violet, blue, and pink flowers; short-lived; tolerate warm/hot climates as annuals; giant (3- to 6-foot) heirlooms and dwarf hybrids. ‘King Arthur’, 5 to 6 feet tall, has plum flowers with white centers.
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Comments
There are a few varieties that are biennial and bloom every other year. If you planted 10 plants that were the same variety chances are that the six that didn't come up this year are dead. It's helpful to know the name of the delphiniums that you plant. You can then look them up and get details on the variety.
Cut the plant down to about 6 to 8 inches after the first killing frost in autumn. You can then store the pot in the basement. Just remember to water the plant a couple of times during the winter months just so that the roots don't get too dry.
Hi, Trucia: Delphiniums are not the hardiest plants to divide and transplant to begin with (starting from seed often works better), but if you do wish to divide and transplant, it's best to do it in the early spring, after they've had a chance to regroup over the winter. Then again, there might not be much to lose, so up to you. Thanks for asking!
For heat zones above zone 7, it is recommended that you grow them where they get afternoon shade. Consider them to be short-lived perennials in your zone or you can grow them as annuals.
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Delphiniums don't like "wet feet" and if you have a puddle now it will happen again. The soil needs to drain well so we suggest that you dig up the plants and amend the soil with compost before replanting. Or move the plants to a "drier" location.