Majority of cacti prefer full sun. Indoors, the best light exposure would be near a south-facing window. If that’s not available, a west window is the next choice, followed by east, and lastly north. There are some exceptions to this rule, for example the so-called jungle cacti. Before placing your plant in full sun, check out its specific light requirements online.
This is an easy one - cacti like it cool in the winter (40s and 50s are fine) and hot in the summer.
Cacti prefer, and thrive in, poor soil. Think gravel pit. Your cacti should be in a clay pot that contains a lose mixture of sandy/gravelly soil, with a few small pebbles mixed in. Do not use standard potting soil, or any kind of organic-rich garden soil. Think Arizona desert.
Cacti do not like a ton of water. They really want dry soil, not wet soil. Gravelly soil will ensure quick drainage, which is what cacti want and need. Slow drainage (wet soil) keeps water in extended contact with the roots, which, in turn, promotes the growth of viruses that kill the cacti from the roots up. Most plants can resist the viruses, but not cacti. Here’s a good cactus watering schedule:
November through March – Water twice with a small amount of water. For example, a 4-inch pot will be fine with about 1⁄4 cup, or less, of water. This assumes you have the proper soil in the pot. You know you’re OK if the water quickly passes through the pot and exits out the drain hole in the bottom. The plant can sit in that excess water for up to one hour. When to water? Thanksgiving, New Year’s Day, and St. Patrick’s Day. Remember, when in doubt, don’t water! Finally, cacti like bright light and cool temperatures in the winter. Windowsills that face south or west are best, followed by east. But don’t push the plant up against the glass. Northern exposures are good for artists but not for cacti.
April – Just a little water twice during the month. April 1st and the 15th.
May – First Week: To avoid burning your plant (yes, cacti get terrible sunburns that can kill them) put your cactus outside for the first week of the month, in constant shade. If exposed to the elements do not water it again until you bring it in, come late September. If in sheltered shade (like on a covered porch) continue to water as in April.
Second Week: During the second week of May, put the plant in partial shade, perhaps under a maple tree. This is the week for dappled shade. Let nature water your plant from now through the end of summer.
Third Week, and the rest of summer: Put the plant in full sun. Again, do not water your plant, let nature do it. However, if there is a long summer drought, it’s fine to give your plant a good soaking once in a long while.
June – September – Enjoy watching your plant flower and grow.
October – Bring in your plant before a hard freeze. But don’t be in too much of a hurry. Cacti love chilly nights, if they are dry! If they are wet from a recent rain, and the night temperature will be below 50, bring them in. Do not water again until Thanksgiving Day, and then follow the winter schedule.