Mammillaria vetula is a small cactus that offsets freely to form large spiny clumps. Stems are blue-green, globose to cylindrical, up to 4 inches (10 cm) long, and up to 1.6 inches (4 cm) in diameter. Tubercles are bluntly conical, tipped with 1 to 2 brownish central spines, and 25 to 50 white radial spines.
This plant grows best in full sun or bright direct light, appreciating some afternoon shade in hot weather. Grow in a well-drained cactus mix; adding grit for extra drainage helps, but they are tough plants that tolerate a variety of conditions. Stop watering in the winter and move to a colder location in order to encourage flowering in the spring.