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dahlia classification guide 

dahlia classification guide 

dahlia classification guide 

dahlia classification guide 

dahlia classification guide 

dahlia classification guide 

If you’re dazzled by the abundance of dahlia varieties and wonder how such beauty is organized, you’re in good company.

From fuzzy Sonic Bloom to waterlily Kelgai Ann, dahlias are one of the most diverse flowers in the world, with well over 57,000 registered cultivars! In North America, the American Dahlia Society is responsible for the process of accepting a named variety as a cultivar, and we do our best to adhere to their guide to keep your shopping and learning experiences consistent with the ADS standards. Even if you never plan on hybridizing or showing dahlias, you sure don’t need a degree in botany or a ribbon to know a thing or two about the exciting world of dahlia classification!

Size, Form, Colour, and Class — the identifying blocks behind every bloom

The Four Pillars of Dahlia Beauty

At the heart of it all, dahlias are classified by four main traits:
Size, Form, Colour, and what’s known as their Class, which bundles the other three into a simple, practical code.

Size

From dinnerplate giants to dainty micro blooms, size plays a big role in a dahlia’s personality and garden presence.

Colour

Dahlias boast an impressive spectrum of hues: reds, pinks, yellows, whites, purples, and even near-black…everything but blue!

Form

Dahlias come in all shapes — from mathematically beautiful Ball dahlias to mysterious Cactus dahlias that look like sea urchins

Class

Think of this as the flower’s shorthand ID. A combination of its size, shape, and colour that helps keep things organized.

1234/4

Size

In the classification system, size refers to the diameter of the flower when it's fully open.
Each bloom is measured across its widest point, and that measurement places it into one of six size categories

  • Giant (AA): Over 10 inches wide. These are the showstoppers that turn heads.

  • Large (A): 8 to 10 inches. Still bold, but a bit easier to work with in arrangements.

  • Medium (B): 6 to 8 inches. A versatile size that works beautifully in most gardens.

  • Small (BB): 4 to 6 inches. Neat and tidy, often packed with colour and character.

  • Miniature (M): 2 to 4 inches. Petite blooms perfect for borders or smaller bouquets.

  • Micro (MC): Under 2 inches. These tiny treasures are gaining popularity in floral design.

This is what growers call “form” — the way the petals are arranged, shaped, and how they open.
Dahlia forms range from perfectly round to wildly spiky, and everything in between.

  • Formal Decorative: Broad, smooth petals arranged symmetrically — very tidy, very classic.

  • Informal Decorative: A bit more playful, with petals that twist or curl for a softer, looser look.

  • Cactus & Semi-Cactus: Long, narrow petals that roll or point outward, creating a bold, spiky bloom.

  • Ball & Pompon: Tightly packed petals in a perfect Fibonacci sequence — like little floral marbles.

  • Waterlily: Soft, saucer-shaped blooms with a delicate, almost floating appearance.

  • Collarette, Anemone, Peony: Open-centred forms with layered or textured petals, great for pollinators and cottage-style bouquets.

  • Novelty & Orchid Types: These are the wild cards — forms that don’t quite fit the mould, often with unique petal shapes or open centres.

But when it comes to classification, those colours aren’t just admired, they’re sorted into specific categories. This makes it easier to group similar tones and find just the right bloom for your palette.

  • White, Yellow, Orange, Pink, Red, Lavender, and Purple: These are the solid colours, straightforward and vibrant.

  • Dark Red and Dark Pink: Rich, moody tones that add drama to any arrangement.

  • Bronze: A warm, autumnal hue that’s somewhere between orange and rust.

  • Blends: These come in three types — Light Blend, Flame Blend, and Dark Blend, depending on the intensity and range of the mixed tones.

  • Variegated and Bicolor: These categories cover dahlias with multiple colours on a single petal or bloom, like stripes, speckles, or tips in a contrasting colour.

That’s where Class comes in — a kind of shorthand that combines all three traits into a simple numeric code.

This code isn’t something you need to memorize, but it helps to understand what it’s doing behind the scenes.

Each registered dahlia is given a four-digit classification number:

  • The first digit refers to Size

  • The second to Form

  • And the last two digits to Colour

Let’s look at an example:

Kelgai Ann is a Small (BB), Waterlily (WL), Pink (PK,) Light Blend (LB) dahlia with soft pastel tones. According to the ADS classification system, it’s categorized as 7310 — a small bloom with a water lily shape in the Light Blend colour group.

Visit ADS to learn more about the Classification System