Hydroculture/Substrates

Common hydroponic aggregates. Only materials that have a higher air to water retention ratio are included.

Expanded clay
Expanded clay pellets are a common hydroculture substrate.

Growstones
Growstones are a substrate for growing plants that can be used for soilless purposes or as a soil conditioner. This substrate is made from recycled glass. It has both more air and water retention space than perlite and peat. Another property of this medium is that it holds more water than parboiled rice hulls. Growstones appear to be a comparable alternative to expanded clay aggregate.

Parboiled rice hulls
Rice hulls that are parboiled (PBH) are a substrate or medium for gardening, including certain hydrocultures. This medium decays over time. Rice hulls allow drainage, and retain less water than growstones. A study showed that rice hulls don't affect the effects of plant growth regulators.

Wood fiber
Wood fiber reduces the effects of growth suppressant hormones, used for uniform growth.

Cocopeat
Coco fiber is a common hydroculture aggregate made from coconut hulls.

Gravel
Gravel is good to be layered on the bottom. It allows better drainage near from the plastic net-pot. Placing seeds too close to plastic allows them to rot easier.