36-40" tall. Dahlia Blue Boy is a show-stopping lilac-blue variety that brings a unique color to the world of Dahlias. These well-formed flowers provide dramatic color in flower beds and borders for many months from midsummer. Mix Blue Boy with shades of pink, purple or silver for an outstanding display, or use it to cool down warmer colored flowers. Cold hardy in zones 8-10. In colder zones lift the bulbs in fall and store in a cool place over the winter.