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How to Grow Delphiniums: The Complete Delphinium Flower Guide

purple delphinium flowers in a cottage garden
Image Credit:
seaonweb/shutterstock
Botanical Name
Delphinium
Grown as
Perennial
USDA Zones
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
Toxicity
Toxic
Sun Exposure
Full Sun
Partial Sun
Water Needs
High
Height
3-6 feet
Spread
1–3 feet
Soil pH
Alkaline
Bloom Time
Summer
Flower Color
Blue
Pink
Purple
White
Special Features
Container-Friendly
Cut Flower
Attracts Butterflies
Attracts Hummingbirds
Attracts Pollinators
Deer-resistant
Rabbit-resistant
Resilience
Cold Hardy
Plant Type
Flowers
Written By: Catherine Boeckmann Executive Digital Editor and Master Gardener

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. 

delphinium flowers
Photo:  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’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.

Planting

Choose a spot in full sun with shelter from strong winds. Stake early in the growing season; delphiniums’ 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

  • 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.
purple delphinium flowers against a white fence
Photo: Arty Alison/Shutterstock

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.

Pests and Problems

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

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. ‘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.

Wit and Wisdom

  • The name “delphinium” is derived from the Greek word delphis, meaning “dolphin,” as the closed flower buds were said to resemble a dolphin’s nose.
  • The centers of delphinium flowers are called “bees.”
  • 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. 

Flowers

About The Author

Catherine Boeckmann

Catherine Boeckmann

Executive Digital Editor and Master Gardener

Catherine Boeckmann loves nature, stargazing, and gardening, so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website and is also a certified master gardener in the state of Indiana.

Read more from Catherine Boeckmann

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Comments

<a title="View user profile." href="/author/editors">The Editors</a> Wed, 07/22/2015 - 10:29

Hi, K-Mi: You can always stake anything at any time. What we mean by the advice above to stake when they are small is that this is the best way to help them get tall. But if yours get tall without any staking to begin with, that advice is irrelevant. So go ahead and stake what you have standing. Cut back what has fallen and then stake what regrows when that happens. Good luck and thanks for asking!

 <span>Pollyo</span> Wed, 07/01/2015 - 17:39
Our delphinium have never done well. Out of the original three plants, only one survives (@ 4 years). Now that I've read all these ideas, we're going out back with manure, lime, and two new plants! Wish us luck! We live in central Massachusetts.
<span>Obsessivegardener</span> Sun, 06/14/2015 - 15:29
I have beautiful, green foilage on my 3ft high delphiniums but never any blooms. When they were new, they bloomed the first few years. Now nothing. I keep thinning them out to no avail. Why won't they bloom?
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 06/16/2015 - 15:03

How is the soil? Delphs are heavy feeders: they benefit from fertilizer and/or compost in spring and summer, and some say balanced fertilizer every 2 to 3 weeks, in growing season. Soil must also be well draining. They do not like dry, hot climates; sound like home? They like full sun to partial shade. We're betting that this, in whole or in part, is the main issue.

Do you prune/cut off lateral flower spikes? Doing so may help the main spike to bloom.

Do you cut back stalks to basal leaves in fall? This could help but not until next season, of course.

 

 

 <span>Christine Mavrakis</span> Sat, 06/13/2015 - 03:58
I have a healthy looking delphinium with about 4 flower spikes but 2 of them only have a single flower at the top of the spike and no other buds down the stem! What's going on? I live in the UK.
<span>Caroline Dieterle</span> Sun, 05/31/2015 - 21:45
I have one successful Delphinium plant at one end of a raised bed. (I planted it last year and it came back, looks OK and is budded to bloom). I planted several more this month (May) in the rest of the bed (sandy soil with accumulated compost of several years). They are not wilted or looking distressed EXCEPT that: some of the new plants' leaves are yellow, with the green restricted to the veins, although they not curled and I don't see any insect damage. The yellowed leaves have long petioles. I applied generous amounts of compost today (5/31) and watered it in. I doubt the pH of that soil is as much as 7 and wonder whether I should add lime to make it more alkaline?? But if pH is the problem, why is the first Delphinium I planted last year doing all right?
<span>Sorcha</span> Thu, 06/04/2015 - 13:33
Yellow leaves with green veins is typically an iron or manganese deficiency, which are not typically found in commercial fertilizers. However, it may be that the pH is off and those micronutrients are in the soil, but not available to the plant. There are simple pH testing kits that you can buy at most gardening stores. Make sure that the pH is between 5.8 and 6.5, which is where most plants like it to be.
<span>E Johnson</span> Thu, 05/07/2015 - 13:19
About 2 weeks ago I bought some Delphiniums at the local big box store. I wonder if they have leaf miners? All the older leaves have dead brown edges that curl under. I don't see little lines of eggs on the back, nor actual trails I can follow moving across the face of the leaf. But large areas of the leaves are covered with light tan speckles and thin lines. The area is thickened and very stiff, with a heavy, bumpy texture on the top surface. Can anyone confirm, please?
<span>Chellina</span> Sat, 03/14/2015 - 13:56
I live in North Florida and you can imagine the summers are hot and muggy. I know it's said that growing from seeds is difficult, but I'd like to try. Do you have any tips (if seeds do their thing) for care in this climate? I'm just concerned because: "They prefer moist, cool summers and do not fare well in hot, dry summers." and I'm a mix of the two...the better two I hope. Thank in advance.
<span>Joan</span> Mon, 06/27/2016 - 11:24
I never had any luck until I planted them in a nursery bed in the fall and let them overwinter. I imagine in Florida you'd have to refrigerate the seeds before planting them out.