Dahlia Grading Guide
Dahlia Grading Guide: Understanding Flower Size, Height & Variety
At TB Dahlia, we want our customers to feel confident about the dahlias they're growing. One of the most common misconceptions is that the size of the tuber determines the size of the bloom. In reality, the dahlia variety itself dictates flower size and plant height—not the tuber. This guide breaks down official dahlia grading standards to help you better understand what you’re purchasing.
Why This Matters
Knowing what to expect from a specific dahlia variety helps:
- Set proper spacing in your garden
- Match your blooms to arrangements and design needs
- Avoid surprises at bloom time
Bloom Size Classes (American Dahlia Society Standards)
| Size Class | Diameter | Example Varieties |
|---|---|---|
| AA (Giant) | Over 10″ | Arabian Night – Dinner-plate drama |
| A (Large) | 8–10″ | Café au Lait – exhibition-worthy |
| B (Medium) | 6–8″ | Cornel – garden star |
| BB (Small) | 4–6″ | Jowey Winnie – perfect for beds |
| M (Miniature) | 2–4″ | Mystic Illusion – charming bouquets |
| P (Pompon) | Under 2″ | Boom Boom Red – compact cuteness |
| MS (Micro) | Under 1″ | Lollipop – button-sized delight |
Bloom Form Classifications
In addition to size, dahlias are also classified by bloom form—how the petals are shaped and arranged. These are the main types recognized by the American Dahlia Society:
| Form Type | Description | Example Varieties |
| Decorative | Full, layered petals with no center visible | Café au Lait, Jowey Linda |
| Ball | Fully round, tightly packed petals with no center | Cornel, Jowey Winnie |
| Cactus | Pointed, rolled petals often with a spiky look | Verrone’s Obsidian |
| Semi-Cactus | Less rolled than cactus, but still pointed | Karma Corona |
| Waterlily | Flat, symmetrical blooms with broad petals | Glamour Girl |
| Collarette | Single outer row of petals with an inner collar-like ring of smaller petals | Pooh |
| Single | One row of flat petals and a visible center | Happy Single Flame |
| Single-Orchid | One row of petals, often rolled or twisted | Honka |
| Fimbriated | Petal tips are split or fringed | Tsuki Yori no Shisha |
These classifications help you match flower style with design goals, whether for cutting, arranging, or display.
Plant Height Categories
Height matters for staking, spacing, and placement. Here's how we break it down—with examples!
| Height Class | Typical Height | Popular Varieties |
| Dwarf | 12–18″ | Gallery Art Deco – container-friendly |
| Low | 18–24″ | Happy Single Flame – great for edges |
| Medium | 24–36″ | Jowey Linda – versatile garden staple |
| Tall | 36–48″+ | Arabian Night, Café au Lait – cut flower champs |
Common Use Case Categories
Matching the right dahlia to your goals—cut flowers, containers, or landscaping—makes all the difference:
| Use Case | Description | Recommended Varieties |
| Cutting Gardens | Long stems and large blooms perfect for vases | Arabian Night, Cornel, Café au Lait |
| Container Gardens | Compact, sturdy plants that thrive in pots | Gallery Art Deco, Happy Single Flame |
| Borders & Edging | Shorter plants with vibrant colors for bed edges | Mystic Illusion, Boom Boom Red |
| Statement Plants | Giant blooms for dramatic impact in garden beds | Verrone’s Obsidian, Tsuki Yori no Shisha |
| Pollinator-Friendly | Open center varieties that attract bees & butterflies | Honka, Happy Single Flame |
Why Variety Matters
Genetics & Standards: Each variety is classified by bloom size and form based on American Dahlia Society rules. The tuber size does not affect the final bloom size or shape.
Care Tips:
• Soil, light, and water influence performance—but not classification.
• Pinching and disbudding (removing some flower buds) will yield larger, showier blooms.
• Use a 5‑10‑10 fertilizer (5% nitrogen, 10% phosphorus, 10% potassium) to promote strong roots and more flowers. Too much nitrogen? You’ll get leaves, not blooms.
Busted Dahlia Myths
• “My big tuber = giant bloom” → False. Bloom size = variety.
• “If I grow it well, it’ll be taller” → Not really. Height is genetic.
• “Small tubers won’t grow big flowers” → Not true at all.
What to Look for On Our Product Pages
Each TB Dahlia dahlia listing clearly shows:
• Official Bloom Size Class (AA, A, B, etc.)
• Bloom Form Classification (e.g., Decorative, Ball, Waterlily)
• Expected Plant Height
• Ideal Use Case (e.g., cutting garden, containers)
• Link to This Grading Guide for reference
This ensures you’re planting the right dahlia for your space, arrangement style, and growing goals.
Ready to pick your next favorite? Browse all dahlias