Dahlia imperialis personally I am not big into growing Dahlia’s but I do make exceptions if they are really unique. Dahlia imperialis really is exceptional mature plants grow up to trees up to 30 feet tall but for me here in Kentucky 8 to 10 feet is possible. Once mature it produces clusters of light purple flowers. The main reason to grow the plant is for the foliage and over all look. The stems look similar to bamboo or an Araila tree. The flowers are just icing on the cake for this great plant.? A great plant in the landscape.