LECA (Light-weight expanded clay aggregate) have many uses for houseplants!

You can use them to prop up nursery pots in deep decorative pots, or add them to soil mixes to help them drain better. Use them to create a pebble tray to increase humidity. Or even grow your plants in them via semi-passive hydroponic systems. 

LECA can be re-used over and over again by washing in boil water.