Hydro LECA - Lightweight Expanded Clay Aggregate.
An amazing growing medium made of baked clay pebbles that expand when soaked in water. This provides a perfect growing substrate where airflow isn’t compromised and plants don’t sit in boggy soil. The downside (or upside as some see it) is that it contains no nutrients so you have to add liquid fertilisers to your watering regime.
We personally use it in a semi hydroponic set up in which we stand the LECA filled pot in a saucer of nutrient water at all times, allowing the roots to wick up water as and when they need it.
LECA also makes a great lightweight drainage layer in terrariums and bioactive enclosures.