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Delphiniums: How to Plant, Grow, and Care for Delphinium Flowers | The Old Farmer's Almanac

Delphiniums

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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How to Plant, Grow, and Care for Delphinium Flowers

Catherine Boeckmann
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Delightful delphiniums! The stalwart of many perennial flower gardens and great for cutting, these beauties are grown for their showy spikes of colorful summer flowers in gorgeous shades of blue, pink, white, and purple. 

About Delphiniums

Delphinium is a genus consisting of more than 300 species. Some are annuals, some are biennials, and some are perennials. Some grow easily from seed and some do not. 

Delphiniums are a favorite of many gardeners, but it’s important to understand that they prefer moist, cool summers and do not fare well in hot, dry weather. The plants also dislike sudden wind or rain. Also, except for the dwarf perennials, most delphiniums will need staking to keep them upright.

Delphinium Toxicity

Delphiniums are highly poisonous. All parts of the plant are toxic if ingested, but new growth is particularly poisonous, which means that delphiniums tend to have a higher concentration of toxicity earlier in the year. If 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, but handling the plant can also cause skin irritation; wear gloves when interacting with delphiniums if you tend to have sensitive skin.

Planting
  • Grow in fertile, well-drained soil in full sun to light shade, with shelter from strong winds.
  • Plant in the spring. Prepare the soil, mixing in 2 to 4 inches of compost.
  • Delphinium is a genus consisting of over 300 species—some are annuals, others are biennials or perennials. Some grow easily from seed, others don’t.
  • Dig a hole twice the diameter of the plant’s container. When planting, ensure that the top of the root ball is level with the soil.
  • In the spring, broadcast lime, wood ashes, or a mixture of the two over this alkaline-loving perennial. Learn more about soil amendments.
Growing
  • Insert supports no later than midspring or when the plants reach 12 inches high. Stake the low-growing perennials with twiggy, brushwood support. The taller, large-flowered delphiniums need sturdy stakes.
  • Soil should not dry out. Water plants during the summer if rainfall is less than 1 inch per week.
  • For good-quality flower spikes, thin shoots when 3 inches high; leave a minimum of 2 or 3 shoots on young plants, and 5 to 7 shoots on well-established ones.
  • In growth, water all plants freely, applying a balanced liquid fertilizer every 2 to 3 weeks.
  • 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.)
  • If delphiniums need to be divided in the spring, remove and replant the new little plants growing around the outside of the clump. Discard the hard old heart.
Recommended Varieties
There are dwarf-sized delphiniums and medium-sized as well as tall ones (growing up to 6 feet and higher).
  • Belladonna Group: Upright, loose and branching perennials with single flowers that grow 3 to 4 feet tall. â€˜Blue Bees’ is a Belladonna producing clear blue flowers with white centers.
  • Elatum Group: These are the tallest spiked hybrids growing to 6 feet or more. ‘Blue Nile’ is a medium plant bearing semi-double, bright, and mid-blue flowers with white centers (called bees). ‘Bruce’ is a tall Elatum bearing semi-double, violet-purple flowers, paler towards the center, with brown bees.
  • Pacific Hybrids: Similar to Elatum Group, although not as tall, this hybrid is short-lived and often grown as annuals or biennials. â€˜King Arthur’ bears plum flowers with white bees with 5- to 6-foot tall flower spikes.
Harvesting
  • This elegant flower is good for a cutting garden. If you take the blooms into the house as soon as they open, they will bloom again.
  • Add sugar plus lemon juice and bleach to arrangements of delphinium. You can also use a commercial flower preservative.
Pests/Diseases
  • Susceptible to slugs and snails as well as cyclamen mites.
  • Powdery mildew, Southern blight, bacterial and fungal spots, gray mold, crown and root rot, white rot, rust, white smut, leaf smut, and damping off occur.
Flowers
Perennials

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Comments

Denyse (not verified)

2 months 1 week ago

When you say young ones are poisonous, do you mean 'early in the Spring' young or a plant that is one or two years old, rather than a mature plant of 20+ years? Thank you.

The new leaf growth of delphiniums tends to be the most poisonous exposed part of the plant, so delphinium plants are more toxic earlier in the year than they are later in the year. 

Maryann Starrett (not verified)

1 year ago

Are they poisonous if chewed by a dog ?

Denise (not verified)

1 year ago

Delphiniums are starting to grow nicely, however, noticing a shiny look to some of the leaves. Is that a sign of some disease.

A shiny residue on leaves could indicate that slugs or aphids are present. Check out our pest pages for information about dealing with them!