Put a layer of gravel or small stones in a clay pot's bottom the same size as the cactus' nursery container. Make sure the pot has drainage holes in the bottom.
Plant the cactus in the pot at the same level it occupied in its original container. Use a good commercial potting soil designed for cacti.
Set the plant in the sink. Slowly and thoroughly water the planting medium, soaking it until water runs out the drainage holes. Allow it to drain freely for about 20 minutes. Scattering some gravel or small stones in a saucer and setting the pot on top of them keeps the cactus out of standing water. Cacti cannot tolerate wet roots.
Place your cactus in your home's brightest room. A warm windowsill out of direct sun is a good location. The temperature should be between 65 and 85 degrees Fahrenheit during the spring and summer.
Water your first cactus during the April to October growing season when the top 1/2 inch of soil is completely dry. Examine the plant daily for signs of improper watering. If the cactus begins looking wrinkled, it is not receiving enough water. If the plant shows signs of yellowing, you're overwatering it.
Feed your cactus a good commercial cactus 2-7-7 fertilizer once every other month from April through September. Carefully follow the packaging instructions.
Move the cactus to a cooler spot with less light for the fall and winter from October until April. The ideal temperature is between 45 and 60 F. The garage is a good choice.