GROWING INDOOR CACTI
Many cacti and succulents are extremely well adapted to living in houses where the relative humidity is low (10-30 percent). They require only modest amounts of water and fertilizer, but do need abundant light. They should be placed in a bright, sunny window. Insufficient natural light can be augmented by artificial lighting. A cool white fluorescent tube, or a combination of daylight and natural white fluorescent tubes will give good results. Position them 6-12 inches above the plants, and keep them on for 14-16 hours each day.
Before watering your cactus, check to see if the soil is dry. Then water well, especially in the growing months (April through mid-September) and let the water drain off. In the winter, water sparingly — allow your cactus a rest. Perhaps a sip once a month if required and your cactus is in a hot sunny place. Adjust according to conditions. Some shriveling in the winter is natural — especially when keeping hardy cacti indoors.
Southern and western exposure windows give cacti the sun that they need, although you can possibly store them in a north or east window in winter if you are really careful about the watering. Be careful when first placing a cactus in the window, care needs to be taken so that the plant does not sunburn.
Give low nitrogen fertilizer sparingly (1/4 suggested amount) every other watering April through August especially if the cactus is getting good light and is growing.
Some people grow cacti outside in pots during the growing season and place their cactus indoors for storage during the winter non-growing season.