When planning a garden, you may have given a lot of thought to the colors you want to use, or the time of year you want the flower buds to open. You may not have spent much time thinking about the size of the plants you choose. The height of a flower is an important consideration, though. Mixing low-lying growths with towering blossoms can create a rich, three-dimensional effect. The perennial flowers discussed in this article can reach a height of 12 to 24 inches. They won't grow as high as an elephant's eye, but they will lift their blooms off the ground, a blanket of color floating on a sea of green.