Planting, Growing, and Caring for Delphinium
The Almanac Garden Planner - Use It Free for 7 Days!
Plan your 2025 garden with our award-winning Garden Planner.
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.
About Delphinium Flowers
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.
- 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.
Catherine Boeckmann
ADVERTISEMENT
After the other stalk had been spent, I decided to cut it to make another shoot sprout later in the year. I gave it banana peels because I read that they are great organic fertilizers with high potassium and phosphorous amounts that encourage healthy blooms. I gave it diluted Urea for the high nitrogen count and Neem oil to prevent the return of the Cyclamen Mites, powdery mildew, and other diseases. I've also applied an iron/magnesium/zinc solution to the foliage per the label's instructions for faster and safer absorption. It was a very damaged plant when I first bought it so I tried to give it extra care aside from the plants natural high demands. The PH is right around 6.2.
I tried to keep the soil moist per all the discussion posts I've read but it gets very hot and windy in Houston and the plant would often dry out so fast that I wouldn't be able to keep up with it. Anyway I kept it in partial shade and watered it each time 1 inch of topsoil dried out.
The problem is that I was advised to never let it dry out but constantly keeping it moist might have let to root or crown rot. However I don't see any fungus, there's no pungent smell, and the plant is otherwise flowering through side shoots off the second stalk. I've tried to control its environment but this Delphinium has been a very challenging experiment. I'll apply some more iron application and keep the moisture level even but is there any other preventative measures I can take?
Our only thought is, as noted above, to contact your local cooperative extension and ask the advice of experts there. Being “on the ground” and familiar with local conditions they may have insights or comments.
I reached out to TAMU agriculture and they were great. Thank you for all of your insights, I really appreciate it!
Delphiniums are very difficult to grow from seed. Buy as a potted plant at the nursery- where did you find this info? Delphiniums are so easy to start from seed, just drop them in the fall - presto your will have lost 1/2 your garden to delphs in 3 years!
do the flowers produce seeds to plant new plants?
There are many different varieties of delphiniums—some are annuals, others are biennials or perennials. Some grow easily from seed, others don’t. Climate also plays a part. So the best thing to do is save some seed and sow it in the spring. Hopefully, you will be rewarded!
Hello,
I started some seed on wet paper towels in black styrofoam to go boxes. I started them on 9/6, once they sprouted about 10-15 days later, I plucked them from the paper towels and planted them into to a 72 cell self watering seed starter tray with a clear cover/hood. They have shot up to about 1" tall with 2 very nice leaves. They are currently in my livingroom window. I live in Beaverton OR, zone 6 or 7. My question is, with this being the begining of fall, do I dare move them out gradually now so to get them ready for winter, and if not, will they survive indoors all winter until spring? Or in other words.....HELP!!
Dont get discouraged about growing delphiniums from seed. Use fresh seeds. I put my seeds in plastic egg cartons, and put them in the fridge using damp seed mix. I have good success. They sprout in the fridge. After most have sprouted, put them under a bright light. Normal to cool room temp. Start 10 weeks before last frost date.
I live at 9000' in Colorado and have had huge successes with my delphiniums but this year most of my plants were green and bushy but no blooms, although several did bloom in other parts of my gardens. What is going on??? Thanks!!
