10 Dahlia Flower Forms You Should Know: The Essential Guide to Sizes & Heights
So you’ve fallen down the dahlia flower forms rabbit hole. Welcome.
Let’s be honest, no one tells you when you start growing dahlias that you’re basically signing up for a part-time job trying to tell them all apart.
You start with a few tubers. Suddenly, you’re on garden forums at 1AM googling things like “is this a collarette or just confused?” and wondering how many different ways petals can curl.
To save you from the spiral, here’s a quick, no-fluff breakdown of the main dahlia flower forms, with average bloom sizes and plant heights to help you figure out what’s what. No botany degree required.
Decorative Dahlias
Big, bold, and probably what your brain first pictures when you hear “dahlia.”
Formal Decorative: Perfectly symmetrical petals, almost annoyingly tidy
Informal Decorative: Same general shape but a little more relaxed—like it’s not trying so hard
📏 Bloom size: 4″ to 10″+
🌿 Plant height: 3 to 5 feet
Ball & Mini Ball Dahlias
Tightly packed petals in a round, polished bloom. These are the overachievers—neat, sturdy, and always look like they’ve got it together.
Ball: Slightly larger, very symmetrical
Mini Ball: Smaller, still adorable
📏 Bloom size: Ball: 3.5″–4″ | Mini Ball: 2″–3.5″
🌿 Plant height: 3.5 to 5 feet
Pompon Dahlias
Tiny but mighty. These blooms are under 2 inches and look like perfect little globes. They kind of remind me of those tiny cupcakes you eat a dozen of without noticing.
📏 Bloom size: Less than 2″
🌿 Plant height: 2.5 to 4 feet
Cactus & Semi-Cactus Dahlias
These ones come in loud. Long, pointed petals that curl back like nature’s version of a blowout.
Cactus: Very narrow and sharp-looking petals
Semi-Cactus: A bit softer, still spiky, just maybe less aggressive
📏 Bloom size: 4″ to 10″
🌿 Plant height: 3.5 to 5.5 feet
Waterlily Dahlias
Shallow, rounded petals and a calm presence—basically the yoga teacher of dahlias. Smooth, open-faced, and balanced.
📏 Bloom size: 2″ to 6″
🌿 Plant height: 3 to 4.5 feet
Anemone Dahlias
Fluffy, puffball centers with flat outer petals. It’s like they didn’t fully commit to being a ball dahlia, but they’re still holding their own.
📏 Bloom size: 2″ to 4″
🌿 Plant height: 2.5 to 4 feet
Collarette Dahlias
One row of main petals, plus a little frilly “collar” around the open center. Think of them as the ruffled blouse of the dahlia world. Bees love them, and so do people who like quirky charm.
📏 Bloom size: 2.5″ to 4″
🌿 Plant height: 2.5 to 4.5 feet
Peony & Orchid Form Dahlias
Peony-form: Open centers, loose layers of petals—kind of that effortless “I woke up like this” look
Orchid-form: Narrow, often twisted petals that curl back like they’re doing their own thing
📏 Bloom size: 2″ to 6″
🌿 Plant height: 3 to 5 feet
Stellar Dahlias
Pointed petals that curve inward just enough to make them look fancy without trying too hard. Like decorative meets cactus but with a better haircut.
📏 Bloom size: 3″ to 5″
🌿 Plant height: 3.5 to 4.5 feet
Novelty & Open-Centered Dahlias
The wild cards. These don’t really follow rules—open centers, weird petals, unexpected shapes. Basically, if it doesn’t fit anywhere else, it ends up here.
📏 Bloom size: 2″ to 6″+
🌿 Plant height: 3 to 5 feet
Bonus Facts (a.k.a. Stuff That’s Good to Know)
Bloom size is measured across the open flower, not from bud to bud
Plant height varies based on weather, spacing, soil, and whether the chickens trample it
Open-centered types are often more pollinator-friendly
Some forms are more productive than others—but I’ll save that deep dive for another post
I’m currently working on a free Canadian dahlia directory with variety info, growing notes, and (because I know some of you are just as extra as I am) downloadable ID tags you can print and use in your own garden. Keep an eye on the blog or follow me over at @HER_Homestead_Life on IG for updates.
And if this dahlia flower forms post saved you from a midnight dahlia identity crisis, I’ll consider it a job well done.