Fill the pot with cactus potting mix. Pick up your cactus, place your hand around the base of the plant, and turn the pot over to remove the cactus. Gently tap the roots to remove old soil, and prune off any dead or dried roots. Place the cactus in the new pot and firm the soil around the base with your hands. When the temperatures in autumn begin to drop, it is time to stop watering the crown cactus until spring. When growing indoors or bringing this plant in for winter, avoid putting it in a spot hit by drafts from doors, windows, or heating vents. Grow it in a bright, shady spot with limited morning sun if possible. Fertilizing. Mammillaria s can benefit from fertilization during the growing season. The fertilizer will help them to thrive and bloom. Apply a water-soluble fertilizer for cacti and other succulents. A houseplant fertilizer higher in phosphorus than nitrogen, such as a 5-10-5 solution, can also be used. Wait for the soil in the pot to dry out. Then gently loosen the potting soil in the root ball with your fingers and shake it off. You may see long, well-established roots. Once the soil is gone, trim the roots back by 1/3rd with sharp scissors or pruning shears. Plant into a shallow hole. tI5APiC.