Info from Nourish the Planet.com
Gardeners sometimes deride people lacking in talent for plant care, saying that “they could kill a cactus.” While desert cacti are reputed to be nearly impossible to kill as indoor plants, presumably because of their desert roots, it is crucial to work with their special natures. Unfortunately, if you care for indoor cacti as you do other houseplants, your cacti are doomed for failure.
Once you understand their needs, however, your indoor cacti will thrive under your care.
1. Potting:Pot a desert cactus in a mix of 1 part peat moss, 1 part garden soil and 1 part sand, or a prepackaged mix designed specifically for cacti. Transplant in the spring after the cactus has grown within 1/4 inch of the sides of the pot, but don’t allow it too much extra space — the next pot size up will be adequate.
2. Giving it a home:Place indoor cacti in a window facing south, if possible. Choose an east- or west-facing window otherwise. Supplement with additional bright light for a total of 12 to 18 hours a day during the cacti’s growing season to encourage flowering. Maintain relative humidity of 10 percent to 30 percent and a temperature between 65 and 90 degrees Fahrenheit — glass windows with direct sun can get extremely warm, so keep a thermometer nearby. A hygrometer will help you keep tabs on humidity.
3. The Nutrition:Water cacti when the top 1/2 inch of the growing medium is dry to the touch. Soak the medium thoroughly and allow it to drain when watering — do not leave the cacti constantly sitting in a dish of water, as this encourages rot. Feed cacti from spring to fall with 5-10-10 fertilizer every two to three months, but do not feed immediately after transplantation.
4. The temperature gradient: Move cacti to a location where the temperature ranges from 45 to 55 so they can go dormant for the winter. Water sparingly and from the bottom, just often enough to keep the plants from shriveling — even watering once a week may be excessive, depending on the plant and growing medium. Stop feeding cacti during their dormant period.
Cacti can be the most convenient and contrarily the most difficult pet plant to keep up with. Although they may seem an easier choice, being tough desert plants and all, not providing it undivided attention and essential affection can result in disastrous consequences. And of all the plants in the world, we wouldn’t want to cross a cactus!