Growing Dahlia Flowers:
How to Grow Dahlias Organically

Dahlia flowers are the ultimate showy blooms with colors and shapes to suit every gardener’s preferred palette. They demand to be noticed with pompom, waterlily and quilled petal flourishes. Originating in Mexico, these tender perennials are easy to grow if you follow the right steps for your climate.

Growing Dahlia Flowers: Plant Snapshot

Growing Dahlia Flowers
  • Dahlia (Dahlia)
  • Annual or perennial? Perennial
  • Recommended varieties (by color):
    • Orange: Hamari Gold, Wootton Impact, Shirley Alliance, Frank Hornsey
    • Pink: Rhonda, Pontiac, Fascination, Noreen
    • Red: Bishop of Llandaff, Zorro
    • White: Nina Chester, Small World
    • Yellow: Clare de Lune, Davenport Sunlight, Hamari Accord
    • Two colors:
      • Red/white: Candy Cane
  • Recommended USDA Hardiness zones: 8 to 10
  • Mature Height: 18 inches to 4 feet (45 to 120cm)
  • Mature Spread: 18 inches to 3 feet (45 to 90cm)
  • Sun Requirements: Full sun
  • Blooming season: Mid-late summer
  • Cold tolerance: This tender perennial may need storing over winter
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Growing Dahlia Flowers: Planting the Seed, Transplanting and/or Root Division

Where to Find Planting Supplies...

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Grow seeds by sowing on the surface of pots or a seed tray filled with your own sieved compost or a nutrient-rich seed starting mix. Push into the compost. Cover with glass or a clear plastic bag tied off with a rubber band to hold in the moisture and grow on a windowsill or in a greenhouse.

Once young plants have at least four leaves, pot them up individually. Harden off in late spring, planting out after the last frost has passed.

Plant out tubers six weeks before the last frost in a sunny place with good drainage. Dahlias love rich, well-drained soil. Improve soil with Kelp Meal in early spring if needed. Dig a hole 9 inches (22cm) across and 6 inches (15cm) deep. Put the tuber in the ground and cover with soil. Don’t water at this stage.

Dahlias can be propagated by basal cuttings in the winter or dividing tubers in the spring.

Snapshot: Planting Dahlias

  • Germination soil temperature: 70 degrees F (22 C)
  • Distance between plants: 8 to 18 inches (20 to 46 cm) - the taller the plant, the more space is needed
  • Planting depth: 6 inches (15 cm)
  • Days to germination: 5 to 10 days
  • Preferred soil pH (see soil pH tester for more information): 6.5 to 7
  • Root division information (perennials only):
    • Root system type (clumping, spreading, rhizome or tuber): tuber
    • Roots division frequency: Every year
    • In which season should dividing occur? Spring
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Growing Dahlia Flowers: Dahlia Care

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Wait until leaf sprouts appear to begin watering unless in a hot dry, climate when light watering is recommended. Once flower buds begin to appear water heavily up to three times a week depending on rainfall.

Dahlias are greedy feeders. Start feeding weekly about 6 weeks after planting with an organic seaweed liquid fertilizer. This improves the foliage and flowers. In the autumn, use organic potassium to help the tubers grow as the season ends.

Most dahlia varieties need staking. For larger varieties put a sturdy 3ft (90cm) stake into the planting hole when you plant the tuber. Pinch out the central stem when the plant reaches 15 inches (38cm) to encourage bushy growth and more flowers. Add two more canes either side of the plant and tie in as it grows.

Deadhead or cut flowers regularly to extend the blooming season.

Unless you live in a frost-free area, dahlias need lifting and storing over winter. Wait until the first frost blackens the leaves, then lift, clean and trim the tubers. Store them upside down in a frost-free place to dry out.

Snapshot: Dahlia Care

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Growing Dahlia Flowers: Harvesting/Cutting Time

Dahlias are perfect for providing you with spectacular blooms for floral arrangements. For best results use a sharp knife to cut dahlia flowers in the morning or evening. With continued cutting their bright colors will see you through late summer and autumn.

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Growing Dahlia Flowers: Pests & Diseases

Growing Dahlia Flowers: Pests and Diseases
Dahlias are susceptible to viruses, aphids and red spider mites.

Earwigs love dahlia foliage and can strip a plant’s leaves in just a few days. If earwigs have found their way to your dahlias, try this: lure the earwigs into an upturned, straw-stuffed pot perched on a cane during the day, then remove at night to get them out of your garden.

The following pests and diseases have been known to affect the success of growing Dahlias (see Organic Garden Pest Control for information about how to prevent and address pests and diseases)...

Pests

  • Aphids
  • Broad mite
  • Carrot beetle
  • Cyclamen mite
  • Earwigs
  • Foliage-feeding caterpillars
  • Leaf beetles
  • Leafhoppers
  • Leafminers
  • Mealybugs
  • Red spider mite
  • Root knot nematode
  • Snails and slugs
  • Spider mites
  • Thrips
  • True Bugs
  • Weevils
  • Whiteflies

Diseases

  • Armillaria root rot
  • Crown gall
  • Fusarium wilt
  • Gray mold
  • Powdery mildew
  • Root and crown rots
  • Verticillium wilt
  • Viruses
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