Native to Madagascar, Kalanchoe blossfeldiana comes from warm, bright conditions where water drains away quickly. That background explains its need for a loose, well-drained substrate that dries at a steady pace instead of staying dense or soggy.
The best soil for Flaming Katy feels airy and light, with a sandy-loamy structure and some organic content. Its roots are fairly fine and do best when oxygen can move through the potting medium, while moderate moisture retention helps support growth without keeping the root zone wet for long.