Deciding on Dahlias

The dahlia counts among our most satisfying and popular ornamental plants. It grows easily, blooms over a long period, reproduces generously and returns anew, year after year.

Spanish explorers brought the dahlia from Mexico and Guatemala to Spain in the early 1800s, where it became popular throughout Europe. The arrival in 1872 of a new variety, Dahlia juarezii, inspired hybridizers to create the wide range of dahlias from which gardeners can choose today.

The dahlia-growing year has three phases: selecting the plants, planting the tubers, and enjoying the blossoms. The planting season begins after the last frost (after April 1st for the Monterey Bay area, conservatively) and ends mid-June (earlier is better). The Monterey Bay Dahlia Society schedules its annual sale in early April.

The bloom period begins in mid- to late-July, depending on the cultivar, and continues until frost. In this area, we can leave tubers in the ground to sprout in the spring.

The first phase of the gardener’s annual dahlia-growing plan is to select plants to add to the garden. We might indulge occasionally in impulsive gardening, but planning works!

The time to select plants is now. This may be the dahlia’s greatest challenge. The American Dahlia Society recognizes eighteen forms of the dahlia, fifteen colors or color combinations, and nine blossom size categories. In addition, for each form, hybridizers have produced —and continue to produce—many unique cultivars.

Planning for specific plants also involves choosing a suitable location, which for dahlias means full sun and good drainage. In addition, site selection should consider how the size and color of dahlias would relate to nearby plants. The gardener might visualize a “garden vignette,” a setting in which dahlias would complement other new or existing plants.

There are no compelling rules here, except the tried-and-true “tall plants in back” idea, which concerns only visibility. Many combinations of color and form can be successful, so the individual gardener’s creative and aesthetic senses are most important.

After deciding on a spot for dahlias in your garden, you will have until planting time for site preparation: removing or relocating existing plants, amending the soil, etc.

To choose which dahlias to grow in your garden, know the options. An excellent opportunity for this planning is the Monterey Bay Dahlia Society’s 2012 Annual Dahlia Show, which runs from 1:00 to 5:00 on Saturday, August 25th and from 11:00 to 4:00 on Sunday, August 26th. It will be at Soquel High School, 410 Old San Jose Rd., Soquel, CA. At this free event, local gardeners display hundreds of types of dahlias and compete for awards. Knowledgeable volunteers will offer growing tips and answer questions. Dahlia blooms and plants will be available for purchase as well.


The following information is from the American Dahlia Society.

Blossom Size

  • AA -(Giant), over 10 inches in diameter
  • A -(Large), over 8 to 10 inches in diameter
  • B -(Medium), over 6 to 8 inches in diameter
  • BB -(Small), over 4 to 6 inches in diameter
  • M -(Miniature), up to 4 inches in diameter
  • BA -(Ball), over 3.5 inches in diameter
  • MB -(Miniature Ball), over 2 to 3.5 inches in diameter
  • P -(Pompon), up to 2 inches in diameter
  • MS -(Mignon Single), up to 2 inches in diameter


  • Formal Decorative – Ray florets (petals) are flat, partially revolute (petal edges roll back), or partially involute (petal edges roll forward). The petals are uniform and regularly arranged, tending to curve toward the stem.
  • Informal Decorative – Ray florets are twisted, or curled, or wavy creating an affect that the petals are not flat. The petals may be partially revolute with their arrangement appearing irregular.
  • Semi-Cactus – The ray florets are broad at the base, straight, incurved or recurved and the ray florets revolute for up to one half of their length.
  • Straight Cactus – The ray florets revolute for more that one half of their length; they also may be pointed, straight, or recurved, radiating in all directions from the center of the flower head.
  • Incurved Cactus – These dahlias also have ray florets that are curved for more than one half of the length but the pointed petals have a pronounced curvature toward the center of the flower head.
  • Laciniated – The split or laciniation should be in proportion to the ray floret length. There should be an overall twisting in the area of the split involute or revolute ray florets, to give an overall fringed effect.
  • Ball – fully double flowers, ball shaped or slightly flattened at the face, and the ray florets are blunt, rounded, or indented, involute for most of their length, fully involute for about one half their length, and normally displayed in a spiral arrangement.
  • Miniature Ball – Same form as ball dahlia , differing only in size.
  • Pompon – Fully double flowers similar to ball dahlias but more globular and smaller in size; also, the ray florets involute for their whole length and fully involute for more than half of their length.
  • Stellar – Fully double, breaking gradually from immature florets to fully developed outer florets. The outer florets should be narrow and involute with a slight recurve to the stem. The less mature florets should possess the same narrow and partially involute characteristic. The depth of the stellar dahlia type should be from one half to two thirds the diameter of the bloom, the greater depth being the ideal.
  • Waterlily – Fully double and symmetrical blooms with a side view that appears to be flat or saucer shaped. The ray florets are openly faced giving the bloom a delicate appearance. The center is closed and dome shaped breaking gradually to four to seven rows of fully developed outer ray florets which are also broad and slightly cupped.
  • Peony – An open centered dahlia with two or more rows of ray florets surrounding the disc flowers (small tubular florets which make up the central part of the flower. Each has a pistil and stamens but generally no other conspicuous flower parts). Ray florets adjacent to the disc flowers may be smaller, twisted, and/or curled.
  • Anemone – Dahlias with one or more rows of ray florets surrounding a center of elongated tubular disc florets. These disc florets should be fully developed and present a domed, pincushion appearance.
  • Collarette – An opened faced dahlia with a single row of uniform evenly spaced compound ray florets in a flat plane surrounding the disc flowers. The petaloids that surround the disc are less than one-half the length of the ray florets.
  • Single – An open faced dahlia with a single row of uniform evenly spaced ray florets in a flat plane surrounding the disc flowers.
  • Mignon Single – Same as single, differing only in size.
  • Orchid – An open centered dahlia with a single row of evenly spaced ray florets in a flat plane surrounding the disc flowers. The ray florets are involute for 2/3s or more of their length and fully involute for at least 1/3 of their length.
  • Novelty Open – Dahlias with characteristics differing from the present classifications. These dahlias will have a disc center.
  • Novelty Fully Double – Dahlias with characteristics differing from the present classifications. These varieties will have a fully double center.


1) White

2) Yellow

3) Orange

4) Pink

5) Dark Pink

6) Red

7) Dark Red

8) Lavender

9) Purple

10) Light Blend – a blending of the lighter tints and tones of pink, yellow,lavender, and other pastels

11) Bronze

12) Flame

13) Dark Blend

14) Variegated – where two or more colors appear on the face of the bloom either in dots, splashes, stripes on narrow lines

15) Bicolor – blooms with two distinctly clear and sharply separated color

2 thoughts on “Deciding on Dahlias

  1. I love dahlias – they remind me of my Grandad’s garden in Liverpool, England. And maybe I’ll try them again. In my garden I need to use gopher baskets, and for Dahlias, I need to remember and let the baskets come up a few inches above the soil too. I was so sad when I came out one morning to find my lovely dahlias all on their sides, roots totally gone! Thanks for the tip that it’s a good time to select some dahlias now!

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