Note: The China Lecca is a bit moist. LECA is an acronym for Lightweight Expanded Clay Aggregate. They are baked clay balls that expand. Due to the expansion, they can soak up water. The porous surface allows roots to have something to grip onto. As they are made of clay, they do not contain any nutrients. You will need to add nutrients for the plants into the water. LECA is most commonly used for hydroponics. Due to its size, it ensures good root aeration. It can be mixed into soil to promote drainage or be simply put at the base of the pot before adding soil on top as a space filler to reduce overall pot weight. It can also be added on top of soil to reduce moisture loss and reduce evaporation. As LECA is non-organic, it's a sterile medium which reduces pests. For a 4 tier hydroponic system, you will need either: -3 bags of German Leca (8-16mm) 1.5kg -3 bags of German Leca (4-8mm) 1.5kg You can use German Leca (8-16mm): If you are intending to sow the seeds in a separate medium and transplant the seedlings into your hydroponics system German Leca (4-8mm): If you are intending to sow the seeds directly into your hydroponics system