Zinnia grandiflora is a small flat-topped or rounded subshrub growing up to 22 centimeters (8.8 inches) tall with many slender, branching stems. The oppositely arranged leaves are linear and 1 to 3 centimeters (0.4-1.2 inches) long. The herbage is covered in short, rough hairs. The flower head has 3 to 6 bright yellow ray florets each between 1 and 2 centimeters (0.4-0.8 inches) in length. At the center is a cluster of several tubular disc florets. It grows on plains and foothills and other dry habitat.