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

Delphiniums

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Delphinium
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How to Plant, Grow, and Care for Delphinium Flowers

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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’re 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 flowers 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’s important to know about delphiniums is that they will thrive as long as you meet their specific conditions. Delphinium prefer moist, cool summers; they do not fair well in hot, dry weather or sudden wind or rain, which can know them down. Most varieties will need staking. See more detail 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, but 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
  • 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 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

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.

Wit and Wisdom
  • The name “delphinium” is derived from the Greek word delphis, which means “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. 
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

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