Giant reedis a robust perennial grass that can grow to 20 ft tall. Each plant has many stiff and hollow stems that form cane-like clumps and spread vegetatively by rhizomes. The stems resemble corn stalks and have long, flat leaves up to 1.5 ft long that can appear variegated. The alternate leaves are pale green to blue-green and clasp the stem with a heart-shaped base. Flowers form in dense plumes at the top of the stalks from late summer to early fall. The flower plumes themselves can reach 3 ft in length.