Watering a cactus requires careful consideration to ensure optimal health and growth. Start by selecting the right cactus for your environment and providing it with an adequate amount of light.
Next, wait until the soil is completely dry — which can take up to three weeks, depending on humidity — before you water. When you’re ready, thoroughly soak the soil until water drains from the bottom of the pot. After that, wait again for all the moisture to be absorbed before watering again.
Different varieties will require different amounts of water at different times; some require more frequent watering than others, and some need more during certain times in their growth cycle. Monitor your cactus closely and observe its reactions in order to best understand its habits.
When it’s time to water your cactus, use room-temperature filtered or distilled water if possible — tap water may contain too much chlorine or fluoride, which can damage the plant over time — and don’t leave your cactus sitting in water; it needs time to absorb what it needs and then let excess run off through drainage holes at the bottom of the pot.
Finally, remember that overwatering is worse than underwatering as it leads to root rot or stem rot due to fungal problems. If you’re not sure when you should water a specific variety of cactus, err on the side of caution and give it just a little bit less than what you think it needs!