Light: Mammillaria species appreciate strong light, but many species dislike more than four hours of direct summer sunlight. Provide bright, even light for the best results. Water: 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. Soil: A rich, fast-draining cactus mix is ideal. Fertilizer: During the growing season, fertilize with a cacti fertilizer mix. Suspend feeding during the dormant winter period.