Decorative dahlias are exactly that—decorative. All are double flowers, but are classified as formal if their petals follow a regular pattern, and Informal if their petals seem to wave or curl in a freer fashion. Decorative dahlias don't show a disc and the flowers are usually fairly wide and flat. The petals are involute (or curled up at the edges) as they leave the centre, but flatten and become blunt towards the end. Whether you're going for a mass showing of colour, or for giant blooms, you will find them in this decorative dahlia category, where the bloom size varies from miniature 10cm flowers covering compact plants, to giant-sized dinnerplate dahlias with diameters of up to 25cm.