How to Grow Mammillaria Mystax As a House Plant

Select a pot just big enough to hold the Mammillaria mystax, with at least one drainage hole in the bottom of the pot. Fill the bottom 1 to 2 inches of the pot with pea gravel or small rocks to improve drainage.

Mix 1 part garden soil, 1 part coarse builder's sand and 1 part peat moss as the planting medium. Cacti do best in sandy, well-draining soils. Garden centers also sell planting mix specifically designed for cacti.

Plant the cactus in your pot, placing the ball of the cactus slightly above the soil level and just covering the roots. This keeps the plant from direct contact with wet soil.

Place the cactus near a window where it receives light most of the day. Windows with southern or western exposure provide the best light. Cacti withstand fairly wide changes in temperature, ranging from 40 to 90 degrees F. Night temperatures between 45 and 50 degrees F stimulate flower production. In colder climates, monitor the temperature in winter if the cactus sits on or near windowsill. Do not let the plant's night temperature drop below 35 degrees F.

Water the cactus according to its growing cycle. During the dormant winter season, water actually does more harm than good. The plant needs a long, dry winter to thrive. Begin watering in the spring, when the cactus shows signs of new growth. Water when the soil is dry to the touch. As the summer progresses into fall, the plant requires less-frequent watering.

When you do water the cactus, water it thoroughly. Shallow watering does not benefit the plant. Add water until it begins to drain out the bottom of the pot. Let the cacti dry out between watering. The plant may need water only once a month over the summer.

Transition the plant in the spring and fall by gradually increasing or reducing the water amount based on the needs of the upcoming season.

Fertilize the cactus with a time-release fertilizer in the spring, or with a 5-10-5 plant food mix applied in spring, summer and fall.