The watering requirements for a Christmas cactus depend on the time of year. During spring, summer, and fall, water the plant regularly when the soil is dry to the touch, but do not overwater it. During the winter, when the plant is dormant, reduce watering significantly. Watering a cactus is a balancing act, so make sure not to overdo it. Overwatering can lead to root rot, while under-watering can cause the plant to wilt.