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How to Grow Delphiniums: The Complete Delphinium Flower Guide

Photo Credit
seaonweb/shutterstock
Botanical Name
Delphinium
Plant Type
Flower
Sun Exposure
Full Sun
Part Sun
Soil pH
Alkaline/Basic
Bloom Time
Summer
Flower Color
Blue
Pink
Purple
White
Hardiness Zone
3
4
5
6
7
Special Features
Attracts Butterflies

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Planting, Growing, and Caring for Delphiniums

Catherine Boeckmann

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.

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Planting

Choose a spot in full sun with shelter from strong winds. Stake early in the growing season; delphiniums鈥 heavy flower spikes grow on hollow stems, which can easily break. Soil should be fertile, well-draining, and neutral to slightly alkaline (pH of 6.0 to 7.5). Prior to planting, loosen the garden soil and mix in 2 to 4 inches of compost or aged manure. Do a soil test and, if needed, add lime, wood ashes, or a mixture of the two to this alkaline-loving perennial.

When to Plant Delphinium

  • Plant delphinium in the spring as a transplant (small plant started by garden nursery)
  • To start indoors, sow seeds about 10 weeks before the last spring frost.

How to Plant Delphinium

  • Dig a hole twice the diameter of the plant’s container.
  • Make sure that the top of the root ball is level with the surface soil.
  • Fill in with soil.
  • Water thoroughly

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

Types

Delphiniums are hardy in Zones 3 to 7. Most varieties today are not wild but the result of hybridization since the 19th century. Dwarf-, medium-size, and tall (6 feet and up) hybrids are available:
  • 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. 鈥楤lue Donna鈥 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. 鈥楢urora Deep Purple鈥 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 鈥楰ing Arthur鈥, 5 to 6 feet tall, has plum flowers with white centers.

Harvesting

This elegant flower is good for a cutting garden. Cut flowers for arrangements when at least one bud is showing color and one bud is starting to open. Vase life is 6 to 8 days.

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Wit and Wisdom

  • The name 鈥渄elphinium鈥 is derived from the Greek word delphis, which means 鈥渄olphin,鈥 as the closed flower buds were said to resemble a dolphin’s nose.
  • The centers of delphinium flowers are called 鈥渂ees.鈥
  • Don’t get discouraged if you try to grow delphinium from seed. Use fresh seeds; put them in egg cartons in the fridge using damp seed mix; after most have sprouted, put them under a bright light. Normal to cool room temp. 

Pests/Diseases

Diseases: aster yellows, blight, leaf spot, downy mildew, powdery mildew, mold, crown and root rot, gray mold, rust, viruses, smut,  and wilts.
Pests: cyclemen mites, nematodes, slugs and snails

Flowers
About The Author

Catherine Boeckmann

Catherine Boeckmann loves nature, stargazing, and gardening so it鈥檚 not surprising that she and The Old Farmer鈥檚 蜜桃恋人 found each other. She leads digital content for the 蜜桃恋人 website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann
 

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Comments

There are several reasons for brown foliage on delphiniums. Sometimes it's overwatering. Sometimes it's lack of nutrients; delphiniums are heavy feeders and appreciate compost and fertilizer.
Towards the end of their cycle, the foliage simply turns brown as it dies down naturally. They should be back next year.

juliett (not verified)

10 years 3 months ago

The rain has pummeled my Delphiniums so that they are lying on top of each other on the ground and the stems snap when I try to lift and re-stake them. Mostly they are starting to go to seed. Would it be ok to cut them close to the base so I can clean up this tangled mess or should I do my best to remove only the spikes and leave the rest until the stalks turn Brown, or something else? The flower bed is HUGE and almost completely comprised of tall Delphiniums.

Hi Juliett,
Just cut the spikes to the ground leaving any remaining foliage. Water and your plants may regrow another flowering spike before the end of the season.  

Dwight Schmitz (not verified)

10 years 4 months ago

A couple of years ago I rebuilt our raised flower garden in our back yard using PT wood and everything we planted there (phlox, saliva, foxglove, lilies, etc.) has thrived so when it came time this year to rebuild the raised flower bed in our front yard, I felt confident using PT wood. I made a "concoction" of dirt using Scott's topsoil (they say it contains peat moss, but it can't be much), garden soil, additional peat moss (to keep the ground loose) and I threw in a little milorganite to boot. About a week ago we planted phlox and delphiniums and, after planting, I soaked the bases of the plants with Miracle-Grow's QuickStart (I followed the directions). The next day I soaked the ground with water and the third day another dose of the QuickStart. I've been watering every day since. The phlox are THRIVING!!!! It's only been a week and they all have new stems with buds coming up. The delphiniums, on the other hand, while not appearing to be dying, don't seem very "happy." The leaves are green, but all the edges of the leaves are drooping. Am I just being impatient or am I doing something wrong? Thanks!

We really enjoyed your post and hearing about your gardening experience. Congrats on the phlox success. In terms of the delphiniums, perhaps it's just wilting with the heat. Be sure to deadhead delphs after blooming, too. All the best!

Not sure it can be from the heat. It's the end of July and we're still waiting for summer! We've had about four days in the low 90s, maybe two weeks total in the 80s, the rest of summer has been 70s (even came close to breaking a record low for last monday). If I understand correctly, once the delphinium flowers die, they should be deadheaded asap? Thanks!

I have a couple of delphinium plants that have been consistently pathetic looking. They don't grow, never bloom and just take up space. I finally read somewhere that they like an alkaline environment, so I put some lime around each one. Well they are both putting up new sprigs. I wish I knew this earlier.

Delphiniums like moist soil, not soggy and not dry. Try to water deeply a couple of times a week. Adding mulch around the plants will help to keep the soil moist and the roots cool. Deadheading spent flowers will promote new growth and maybe more flowers before the end of summer.

Dwight Schmitz (not verified)

10 years 4 months ago

Soory! Forgot to mention that I live in Wisconsin, zone 5.