Planting, Growing, and Caring for Delphinium
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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
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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.
There are two conflicting suggestions on this page regarding the ideal soil pH for growing delphiniums. The intro says they are alkaline-loving, but later you say that the soil pH should be between 5.8 and 6.5. A pH of anything less than 7 is considered acidic, not alkaline (basic). Please clarify what the ideal soil pH should be for successfully growing delphiniums. Thank you!
After many years of growing Delphiniums, I
finally figured out how to protect them during our often snowy winters in
New York. And I 'm gardening in very large pots on a terrace.
I don't have to lift them or bring them inside.
I just put sand around (not on) the plants so
that even as the snow melts, even if it's a rainy
winter, they have good drainage.
You can get the sand at most hardware stores.
I now lose very few delphiniums
I currently have 5 that are two years old
and 3 that are 3-years old.
They don't last forever, but if you their roots
have lots of room to grow, they can become very
tall--even over 2 years.
Some are now six feet tall, and even in containers,
they have spread to 2-3 tall delphiniums that bloom
twice each summer.
Thanks for catching that! The information in the intro is correct: Delphiniums prefer alkaline soil, not acidic. Your soil should stay on the lower end of alkaline (between 7 and 9 pH), however.
I live in Minnesota. Last year I planted some potted Emperor Delphiniums (dark deep purple with white bee) And one or two light blues, they grew about 2ft. With at least 2 stalks. After fall was well over and just before winter began I cut all of them back. It’s finaly spring here no more snow all the snow I think has finaly melted and we have had 4 days of over 58* degrees in a row w/ no weather below 60 in the forecast.. other spring flowers are growing out of ground. Dafadiles etc. when will my DELPHINIUMS start to show some effort of growing my garden is bare.
Bought this plant in full bloom 2 years ago and planted it in a new bed with fresh deep earth and mulch. It has half a day in full sun and half a day in shade. It grows nice strong thick 5 to 7 leafy stalks growing tall to about a yard and a half tall, and puts all its growing to growing green and tall throughout the spring and summer but for the last two years , no flowers at all. How can I get this plant to produce flowers?
I don't know what the dead part looks like. Sometimes I think the white is dead, but other white looks like it's the new blooms starting. What is the green pod? Should I remove it. The only thing I am confident about is when the blue dries out!
Could you post pictures of the parts and what to deadhead?
Sounds like to me, you did not get any pollinators (Bee’s or butterfly’s) that first year they were planted. Awe that’s sad. It’s best to plants several pollinator favorites together at the same time. To guarantee they smell and will come. Marigolds, purple hyssops, Phlox and candy tuff, they like keep in mind flowers are Regional and species by favorite. Meaning each region has specific butterfly’s and therefore each species has their favorite flowers. Check for the species that favor your region and plant their specific favorite flower .. I don’t know if it is too late for your flowers to bud.
Hi I bought some beautiful delphinium plants mid July. The nursery had them in the Perennial section. I hooked the informations to each plant but either birds ran off with them or ? Anyway...they all went to seed and I took all the little pods off and emptied the seeds into baggies. Now Im wondering if that was right? Should I go dump the seeds with the plant? Im not a good gardener...Ive been told non jokingly that I should not have a yard! I agree. So what do I do with the seeds? Deb
