Perlite

Perlite is a non-renewable resource that can be used as a soil amendment or alone as a medium for hydroponics or for starting cuttings. Due to its drainage properties, perlite has value as a natural filtration system, allowing excess water to easily drain away while retaining a little moisture and catching nutrients that plants need to grow. While perlite is very popular as a soil medium, it is also extremely useful in hydroponic gardening as well.

Vermiculite

Vermiculite can be found in potting soil or purchased by itself in various sizes. The smallest size of vermiculite is used to germinate seeds as a growing medium and the largest size for improved soil aeration. comparing perlite vs. vermiculite, vermiculite is very moisture retentive.

Rock

Various rocks are also a valid form of growing medium providing you have water readily available in the form of a hydroponics system that brings water frequently or continuously such as with top feed, drip systems.