Named after the Swedish botanist Dr. Anders Dahl, and originating from Central America, Dahlias are a bit of a Marmite plant; a love/hate thing. I think in the right context they can be a great addition to the late summer/autumn garden and I think they look particularly elegant in planters, in more formal gardens and in tropical style garden plantings where their bright colours can be framed by lush foliage plants. They are also excellent cut flowers.
Here are my delightful Dahlia tips!
Pick a sunny spot with good humus-rich soil.
Stake them before they flower - I usually break old canes into appropriate sized lengths (approx 50cms) and tie each stem in with garden twine.
Do this frequently to keep the plant flowering. The spent blooms are cone-shaped, unlike the new flower buds, which are round.
When the plant has finished, after cutting the stems to the base, you can either, Option A, mound up some compost over the tubers and mark them with one of your stakes (remove their 'bedding' when the frosts are over, sometime in May) or, Option B, dig the tubers up, shake off the soil and store in a dark, dry, frost free place and then replant them (again, sometime in May). If you have a lot of badgers or squirrels, or wet soil over winter (in which the tubers may rot) you might want to opt for Option B!
You can eat the tubers (peeled and steamed) and the flowers (raw) should you want to!