Native to the southwestern US and northern Mexico, Cylindropuntia leptocaulis grows in dry ground with sandy, loamy, or rocky textures. That habitat explains why Christmas cactus soil should drain quickly and stay airy, rather than holding moisture around the roots for long periods.
Its roots are adapted to brief moisture followed by fast drying, so loose mineral-rich soil suits the plant better than dense, rich mixes. Slightly acidic to slightly alkaline conditions are acceptable, but the most important trait is a well-drained structure that keeps oxygen around the roots.