Mammillaria hahniana is a sun-loving cactus that forms large groups. It grows up to 10 inches (25 cm) tall and up to 20 inches (50 cm) broad. The solitary spherical stems, up to 5 inches (12.5 cm) in diameter, are covered in white down and white spines. Reddish purple flowers, up to 0.6 inches (15 mm) in diameter, are borne in spring and summer, sometimes forming a complete ring around the apex of the plant. These cactus prefers bright light and ample airflow. Outside it likes full sun or afternoon shade. Allow the soil mix to become nearly dry between waterings, but then water thoroughly. Immaculate drainage is essential, so never let the pots sit in water. Suspend watering in the winter, but mist occasionally.