Best dahlia cultivars by size and form

Dahlias are summer-to-fall blooming plants grown from tuberous roots. They are tender perennials -- reliably perennial only in zones 8--11 where ground doesn't freeze. In zones 3--7, tubers must be dug in fall and stored indoors, or treated as annuals with new tuber purchase each.

Dahlias are summer-to-fall blooming plants grown from tuberous roots. They are tender perennials — reliably perennial only in zones 8—11 where ground doesn't freeze. In zones 3—7, tubers must be dug in fall and stored indoors, or treated as annuals with new tuber purchase each spring.

I don't grow dahlias at home. The deer pressure and the annual digging/storage requirement make them lower priority than the perennials I've committed to. This guide draws on the American Dahlia Society's classification system and Extension data.

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Dahlia classification

Per the American Dahlia Society, dahlias are classified by flower form and size. Key forms:

• AA (Giant): over 10 in diameter
• A (Large): 8—10 in
• B (Medium): 6—8 in
• BB (Small): 4—6 in
• M (Miniature): under 4 in
• P (Pompom): under 2 in, fully double, globe-shaped

Forms by petal arrangement:

• Formal decorative: fully double, evenly arranged, formal appearance
• Informal decorative: fully double, irregular petal arrangement
• Ball: more than 2 in; rounded, fully double; petals blunt-tipped
• Pompom: under 2 in; fully rounded globe
• Waterlily: fully double, petals wide and flat, shallow flower resembling waterlily
• Cactus: petals rolled back into quills
• Single: one row of petals with visible center