The Christian Science Monitor has published this anecdotally proven method:

“The important thing is to water the cactus at exactly the right intervals. These plants came from the desert near Tucson, Ariz. When I brought them back to Boston, I immediately subscribed to an Arizona newspaper. And when the paper says it rained in Tucson, that’s when I water my cactus plants. As you can see, so far it’s worked well.”