The watering frequency for cactus plants depends on several factors, such as the size of the pot, the type of cactus, and the growing conditions. In general, cactus plants require less water than most other plants, and should be watered only when the top inch of the soil feels dry to the touch. Overwatering can cause root rot and other problems, so it's important to use a well-draining soil mix and avoid letting the plant sit in standing water. As a general guideline, cactus plants may need to be watered every 2-4 weeks, but it's best to monitor the soil moisture level and adjust watering accordingly.