From midsummer to frost, count on dahlias to provide lavish blooms in a myriad of colors, including white, soft pink, lavender, fiery orange, crimson, and deep red.

There are 11 classes of dahlia, each with a distinct flower form. Some cultivars have flowers the size of golf balls, and others have blooms as large as dinner plates. Dahlias vary in height as well, reaching from 12 inches to 8 feet tall. Short dahlias make attractive border and container plants, and tall dahlias are stately additions to the back of the garden.

Plant Facts
Common name: Dahlia
Botanical name: Dahlia
Plant type: Tuberous tender perennial
Height: 12 inches to 8 feet tall
Zones: 9 to 11 as a perennial
Family: Asteraceae

Growing conditions:

  • Sun: Full sun to part shade
  • Soil: Humus-rich, well-drained soil
  • Moisture: Consistently moist, but not constantly wet.

Care

  • Mulch: Apply a 2- to 4-inch layer of mulch around dahlias to retain moisture and control weeds.
  • Fertilizing: Use a high-nitrogen fertilizer weekly until midsummer, then switch to a high-potassium fertilizer weekly until the end of summer.
  • Pruning: Remove faded flowers to encourage more flowering.


Cultivars

  • There are hundreds of cultivars, but here are some favorites:
  • ‘Mom's Special' (pictured) is a white dinner-plate dahlia with streaks of soft lavender. Grows 36 to 48 inches tall.
  • ‘Bishop of Llandaff' is an heirloom with dark mahogany foliage and garnet- red flowers. Grows 24 to 36 inches tall.
  • ‘Gallery Monet' has creamy petals brushed with rose and a bit of yellow in the center. Grows 12 to 24 inches tall.
  • ‘Night Queen' has claret, almost black, ball-shaped flowers. Grows 36 to 48 inches tall.


Garden notes

  • Plant in April to May when soil is 58ºF to 60ºF.
  • Plant in soil with peat moss, organic matter, and bone meal mixed into it. Tubers rot in poorly drained, heavy, wet soil.
  • In climates colder than Zone 9, cut foliage to about 2 inches high after the first killing frost in autumn. Let the tubers cure a few weeks in the ground, and then lift clumps and brush off soil. Store in a covered box lined with a breathable plastic liner filled with perlite, fine sawdust, or peat moss. Space tubers so that they don't touch each other, and dust with bulb powder. Store in a dry area at 45ºF to 55ºF.
  • Before planting the following spring, divide large clumps into sections, making sure each one has one or more eyes. Eyes are tiny bumps or slightly indented craters.

Pests and diseases

  • Aphids, stem borers, spider mites, and slugs may attack dahlias.
  • Powdery mildew, fungal leaf spots, and blossom blights can occur.
  • Dahlia mosaic viruses, smut, and tomato spotted wilt virus are other diseases that attack dahlias.

All in the family

  • The Asteraceae group of plants includes a reliable, durable group of perennials including Achillea filipendulina (fernleaf yarrow), Anthemis tinctoria (golden Marguerite), Aster novae-angliae (New England aster), Echinacea purpurea (purple coneflower), and Rudbeckia hirta (black-eyed Susan).


Text by Mary Pestel, Photo courtesy of K. Van Bourgondien & Sons