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Planting, Growing, and Caring for Delphiniums
Delightful delphiniums! 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.
About Delphinium Flowers
Delphinium is a genus in the Ranunculaceae family. (They鈥檙e often confused with larkspur, but these are 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.
Image: Edita Medeina/Shutterstock
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鈥檚 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
- Delphinium 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.
Credit: Arty Alison/Shutterstock
Catherine Boeckmann
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my delphs are well up. should I cover them for -9 degrees c.prediction?
No worries. Delphiniums are a hardy herbaceous perennial, which means they are fully hardy down -10 to -15C and between 5 - 14F. In late autumn and winter they die back completely to bare earth and regrow each spring. Note: They do need shelter from winds and best planted in a sheltered spot away from winds. They have heavy flower heads supported by hollow stems. Also, all delphiniums need staking as soon as they have put on growth and are getting established.
How big should Delphiniums be before transplanting them from under the grow light to outdoors?
Kudos for getting sprouts, Jack. Height is a consideration but you want seedlings with 鈥渢rue鈥 leaves, not just the two that initially appear. True leaves appear early, so if your plants have a couple to a few inches, you’re probably well past that stage. As for height, we’ve see suggestions of 12 to 15 inches but it depends on the strength of the plants. Before transplanting you also want to harden off the plants鈥攇et them used to the world. Here is some advice on that /video/how-harden-plants and another /news/gardening-news/time-get-tough-hardening-plants (these are about vegetables but the process is the same).
We hope this helps!
I want to grow delphiniums indoors in a south-facing window with small period of shade from trees throughout the day .
A/C will be maintained to 80 degrees or less
Any chance of success?
Hello, my wife and I really like delphiniums but we hear that they are very difficult to grow here in the coastal southeast, zone 8b. Nevertheless I purchased some and planted in good, composted soil. What tips can you give me that would heighten my chances of success? Also are there any varieties that would do better than others in this area. I realize that they would be only annuals. Thank you.
I live on the southeast coast of Florida, can I grow these in the ground in partial shade?
Delphinium is technically a perennial, but it can be grown as a winter annual in Florida. Otherwise, Florida is just too hot and wet for this cool-weather plant to survive a summer season.
Delphiniums do need full Sun to grow but they prefer cool weather. So let seeds germinate in winter and the plant will bloom in early spring. Once temperatures rise in summer, the plants will fade and you’ll need to remove them.
I have 3 delphiniums (pale blue/white) growing and flowering nicely in a pot on the deck in SW Iowa. How should I winter them to see them grow and bloom in the Spring again?
As noted at the top of this page, delphiniums can be a challenge; not all grow as perennials. Many are short-lived plants. Knowing that, you could experiement: Cut them back as advised in Care above. Put them into a garage or basement and water them occasionally. Or, if you are in zone 7 or lower, lift them from the pot now and plant them (you could also plant the pot), then lift them in the spring and repot to see if they come back.
