Grow mini cactuses in pots indoors for a low-maintenance, hardy houseplant. The plants require very little care to thrive. As long as they get lots of sun and are in a well-draining environment, mini cactuses grow happily for years. Proper potting is important in growing a healthy plant. The right potting soil and the care right after planting are critical for success. You can put your potted mini cactus outside in summer but be sure to bring it in before winter weather sets in since cactus plants tend to be frost-tender.
Select a pot 1 inch larger than the root mass or the nursery pot the mini cactus is currently in. Make sure the pot has at least one drain hole in the bottom to prevent excess water from accumulating around the roots. Mini cactuses grow well in 2- to 4-inch pots.
Spread a 1/4 to 1/2 inch of fine gravel in the bottom of the pot. Add a commercial potting soil formulated for cactuses and succulents -- regular potting soil holds too much moisture for a cactus.
Slip the mini cactus out of the nursery pot. Wear gloves to protect your hands from the sharp thorns. If the pot doesn't slip off the roots easily, give it a gentle squeeze to loosen the soil.
Place the mini cactus upright in the new pot. Hold it with the base of the stem 1/4 inch below the lip of the pot. Add more soil under the roots if you need to until the cactus sits on its own in the pot. Fill in around the root ball and gently press the soil down with your fingertips.
Place the pot in a sunny spot after planting. Wait to water for two full weeks after you pot the mini cactus. The disturbed roots establish themselves better if left dry for a two-week period after planting.
Water once a month in winter and twice a month in spring, summer and early fall. Place the pot in the sink and run water over it until the liquid starts to drip out the drain holes in the bottom of the pot. Let the pot drain and then place it in a sunny window or outside in hot weather.
Fertilize mini cactuses every other month in spring and summer. Select a 5-10-10 fertilizer and apply it according to the manufacturer's instructions. Water well after fertilizing.