Tuberous Mexican perennial bred over centuries into vast colour and form range — pompon, cactus, decorative, single, and waterlily flower forms across the whole spectrum of warm colours.
Hardiness ratings
| System | Rating | Temperature range | How to read it |
|---|---|---|---|
| USDA hardiness zone | Zone 7–11 | −17.8 °C to 10 °C | Plant tolerates down to this zone |
| RHS hardiness rating | H3 | −5 °C to 1 °C | Plant needs at least this level of cold tolerance |
| Canadian plant hardiness zone | Zone 8–9 | −7 °C and warmer | Plant tolerates down to this zone |
| Australian (ANBG) zone | Zone 3–7 | −5 °C and warmer | Plant tolerates down to this zone |
About Garden dahlia
Dahlias are native to Mexico and Central America, where the tubers were grown as a food crop and used medicinally before the plant was taken up in Europe as an ornamental. It is the national flower of Mexico. Their genetics are unusual — most garden dahlias are octoploid, carrying eight sets of chromosomes rather than the usual two — which is part of why the genus has produced such an extraordinary range of flower forms and colours. They are frost-tender, and in cold regions the tubers are lifted and stored over winter.
Growing notes
- Plant in sunny mid- to late-summer borders and as the primary cut-flower crop — flowers from midsummer until first frost, principal autumn cut flower of the cottage garden tradition
- Tubers historically eaten by the Aztec — edible if mild, but flavour varies wildly between cultivars and most modern ornamental cultivars are bitter; not recommended as food today
- Lift tubers and overwinter dry and frost-free below zone 8, or mulch heavily in situ in marginal zones
- Open-flowered varieties (single, collerette, anemone-flowered) far better for pollinators than fully double pompons