Plant baby cacti in a cactus soil mix in a pot with one or more bottom drainage holes. Alternatively, mix your own soil by combining one part sand with one part potting soil. The sand ensures the mix drains well and doesn't become soggy.
Water the newly planted cactus so the soil mix feels barely moist. Allow the soil to dry out completely before watering again.
Increase watering for tropical holiday cacti once the plants have formed roots. Allow the soil to dry almost completely then water until the soil is evenly moist throughout.
Irrigate rooted desert cacti when the soil mix dries out completely. Provide enough water to moisten the soil but not enough to make it overly damp or soggy.