During winter months you can cut back on the watering routine, as cacti become dormant during this time. Generally this means watering every four to six weeks. But you may find that some of your cacti don't need watering at all. So it's important to get to know your individual plants.
When the growing season starts in March, begin to water regularly again.
A tip worth knowing is that if you forget to water your cactus for a few weeks (or months), you can usually always bring them back to life with a little bit of water.