Dahlias are flamboyant Mexican beauties and I wouldn't be without them because they flower continually from July until the frosts intervene as long as you deadhead them. They also thrive in dry summers.
'Ken's Choice' was one of the stars of an RHS Wisley Trial back in 2005, and this newly-bred dahlia gained an AGM.
Buy tubers now, plant in April (under cover) but don't place outside until mid-May or later to avoid cold shocks.
Ideally your plants should be only six inches high when planted, or less. But always stake as you plant using three canes. Then stand back and wait for the floral fireworks!