Native to tropical Southeast Asia, Aeschynanthus radicans grows in warm, humid forests where roots stay lightly moist but still get good airflow. That background explains why it prefers a loose, organic-rich substrate rather than anything dense or heavy.
The best soil for Lipstick plant holds some moisture yet drains freely, with a soft loamy to peaty texture that keeps oxygen around the roots. Its root system benefits from steady moisture and air at the same time, so the substrate should feel open, lightly acidic, and never compacted.