What's an ADS code?
If you've ever browsed a dahlia catalog or wandered through a dahlia show, you've probably seen codes like "0204" or "FD-A-Y" printed next to the variety names. They look like something out of a chemistry textbook, but they're actually a really straightforward system once someone walks you through it.
The American Dahlia Society (ADS) assigns every registered dahlia variety a 4-digit classification code. Those four digits tell you three things about the bloom: how big it is, what shape the petals take, and what color it is. That's it. Once you learn to read the code, you can picture a dahlia before you ever see a photo.
The 4-digit code structure
Every standard ADS code follows the same pattern: [size][form][color][color].
- The first digit tells you the size of the bloom.
- The second digit tells you the form — the shape and arrangement of the petals.
- The last two digits together tell you the color.
So a code like "0204" breaks down as: digit 0 (Giant), digit 2 (Semi-Cactus), digits 04 (Pink). Put that together and you've got a Giant Semi-Cactus in Pink. You already know roughly what it looks like — a huge bloom with partially rolled petals in some shade of pink.
Size codes — the first digit
The first digit tells you how wide the bloom is across its face. This is measured at the widest point when the flower is fully open.
- 0 = AA (Giant) — over 10 inches across. These are the dinner-plate dahlias that stop people in their tracks.
- 1 = A (Large) — 8 to 10 inches. Still big and showy, just not quite dinner-plate territory.
- 2 = B (Medium) — 6 to 8 inches. The sweet spot for a lot of growers. Big enough to appreciate, manageable enough to arrange.
- 3 = BB (Small) — 4 to 6 inches. Great for bouquets and garden beds where you want volume without everything flopping over.
- 4 = M (Miniature) — under 4 inches. Tiny but mighty. These are popular for arrangements and containers.
- 5 = MC (Micro) — under 2 inches. The smallest class. Perfect little gems.
Size is always measured across the face of the bloom, not the height or the overall plant size. A 5-foot-tall plant can have miniature flowers, and a 3-foot plant can produce giants.
Form codes — the second digit
The second digit describes how the petals are shaped and arranged. This is where dahlias really get interesting — the variety of forms is one of the things that makes people fall down the dahlia rabbit hole.
- 0 = FD (Formal Decorative) — flat petals, evenly arranged, no open center visible. Think of a perfectly organized rosette. This is the classic "dahlia" shape most people picture.
- 1 = ID (Informal Decorative) — still flat petals, but the arrangement is more relaxed and irregular. They have a wilder, more organic look than their formal cousins.
- 2 = SC (Semi-Cactus) — petals that are rolled (quilled) for about half their length. They sit right between decorative and cactus forms, with pointed tips but broader bases.
- 3 = C (Straight Cactus) — petals fully rolled into narrow tubes that point straight out from the center. Spiky and dramatic.
- 4 = IC (Incurved Cactus) — same rolled, quilled petals as straight cactus, but they curve inward toward the center of the bloom. Creates a softer, rounder silhouette than straight cactus.
- 5 = LC (Laciniated) — fringed or split petal tips, sometimes called "fimbriated." The edges of the petals look like they've been cut with pinking shears. Unusual and eye-catching.
The special form types
Not every dahlia fits neatly into the size + form grid above. Some types are so distinctive that they get their own two-digit code for the first two positions. When you see a code starting with 6, 7, 8, or 9, you're looking at a special form.
- 60 = BA (Ball) — round, fully double, ball-shaped blooms. The petals curve inward and overlap to form a sphere.
- 61 = MB (Mini Ball) — same ball shape, just smaller. Typically under 3.5 inches.
- 62 = P (Pompon) — very small, perfectly round. Like a mini ball taken to its extreme. Tight, symmetrical, and absolutely charming.
- 70 = ST (Stellar) — pointed petals that curve backward, giving the bloom a star-like appearance.
- 73 = WL (Waterlily) — flat, broad, open blooms with relatively few petal rows. They look like they should be floating on a pond.
- 76 = NX (Novelty Double) — unique forms that don't fit any other category. The "other" box. You'll find some wild-looking dahlias here.
- 80 = PE (Peony) — an open center surrounded by two to five rows of flat petals. Lush and a bit loose.
- 82 = AN (Anemone) — a pincushion-like center of tubular florets surrounded by one or more rows of flat outer petals. Really distinctive in an arrangement.
- 90 = CO (Collarette) — a single outer row of large petals with a "collar" of smaller inner petals around the open center. Two-toned and striking.
- 92 = O (Orchid) — a single row of petals that are rolled or quilled for at least two-thirds of their length. Like a single dahlia crossed with a cactus.
- 96 = S (Single) — one row of flat petals around an open center. Simple, cheerful, and great for pollinators.
- 97 = MN (Mignon Single) — single form, but under 2 inches. Tiny singles that bloom in profusion.
For these special types, the first two digits together identify the form, and the last two digits are still the color code — same as always. So "6206" is a Pompon (62) in Red (06). The size is implied by the type itself (pompons are always small, balls are always round, and so on).
Color codes — the last two digits
The last two digits of any ADS code tell you the bloom color. This applies to both the standard codes and the special form types.
- 01 = White
- 02 = Yellow
- 03 = Orange
- 04 = Pink
- 05 = Dark Pink
- 06 = Red
- 07 = Dark Red
- 08 = Lavender
- 09 = Purple
- 10 = Light Blend — multiple light colors blending together
- 11 = Bronze
- 12 = Flame Blend — warm tones (red, orange, yellow) blending together
- 13 = Dark Blend — multiple dark colors blending together
- 14 = Variegated — streaked or speckled with contrasting colors
- 15 = Bicolor — two distinct colors, usually with a different color at the petal tips than at the base
A few notes on color: the boundaries between some of these can be subjective. Is it pink or dark pink? Lavender or light blend? The ADS classification is based on the variety's official registration, not on what any individual bloom looks like in your garden. Growing conditions, soil, and even temperature can shift the color of a specific flower.
Reading a code — worked examples
Let's put it all together with a few real codes.
"0004" — The first digit is 0 (Giant, over 10 inches). The second digit is 0 (Formal Decorative, flat petals evenly arranged). The last two digits are 04 (Pink). So this is a Giant Formal Decorative in Pink. Think of Café au Lait — that enormous, blush-toned bloom that shows up in every wedding arrangement.
"1204" — First digit 1 (Large, 8–10 inches). Second digit 2 (Semi-Cactus, partially rolled petals). Last two digits 04 (Pink). A Large Semi-Cactus in Pink. Spiky-ish petals on a sizable bloom.
"6206" — Now we're in special form territory. The first two digits 62 tell us it's a Pompon — those perfectly round little globes. The last two digits 06 mean Red. A Red Pompon. Small, round, and vivid.
"9015" — First two digits 90 = Collarette, the ones with a single outer row of large petals and a collar of smaller inner petals. Last two digits 15 = Bicolor. A Bicolor Collarette. These tend to be some of the most visually interesting dahlias you'll see — two distinct colors playing off each other with that layered petal structure.
Notice how the special types work a little differently: the first two digits are the form, and the last two are the color. There's no separate size digit because the form itself implies the size range.
Numbers vs. letters — they're the same thing
You'll sometimes see the same classification written two different ways. A catalog might list a variety as "0204" while a show program writes it as "AA-SC, Pink". Those aren't two separate systems — the letters are just the human-readable translation of the digits.
Here's how the translation works: the first digit 0 maps to AA (Giant). The second digit 2 maps to SC (Semi-Cactus). And the last two digits 04 map to Pink. So "0204" and "AA-SC, Pink" are saying exactly the same thing.
The numeric code is what the ADS officially stores in their database. The letter abbreviations are what growers and judges actually say out loud — nobody calls Café au Lait a "0004," they call it an "AA-FD" or just say "Giant Formal Decorative." But both refer to the same classification. Once you know the number-to-letter mapping, you can go back and forth without thinking about it.
Why this matters
When you're buying tubers from a catalog, the ADS code tells you exactly what to expect before you ever see a photo. That matters when you're comparing 200 varieties and trying to decide which ones to grow this year. A quick glance at the code and you already know the size, shape, and color.
At dahlia shows, judges use these classifications to group entries into the right categories. If you want to compete — or just understand what you're looking at when you visit a show — knowing the codes is essential.
And when you're building a collection, the codes help you spot gaps. Maybe you've got plenty of Formal Decoratives but no Waterlilies. Or you're heavy on pinks and purples but you don't have a single Flame Blend. The classification system gives you a framework to see your collection as a whole, not just as a list of names.
You don't need to memorize every code. Just understanding the structure — size, form, color — turns you from a casual buyer into someone who can navigate the dahlia world with confidence.