Soil is never used in hydroponic growing. Some systems have the ability to support the growing plants, allowing the bare roots to have maximum exposure to the nutrient solution. In other systems, the roots are supported by a growing medium. Some types of media also aid in moisture and nutrient retention. Different media are better suited to specific plants and systems. It is best to research all of your options and to get some recommendations for systems and media before making investing in or building an operation. Popular growing media include:
- Compost bank - It is usually organic and can be used for seed germination.
- Expanded clay - Pellets are baked in a very hot oven, which causes them to expand, creating a porous end product.
- Gravel - Any type can be used. However, gravel can add minerals to nutrient. Always make sure it is clean.
- Oasis - This artificial, foam-based material is commonly known from its use as an arrangement base in the floral industry.
- Peat moss - This medium is carbonized and compressed vegetable matter that has been partially decomposed.
- Perlite - Volcanic glass is mined from lava flows and heated in furnaces to a high temperature, causing the small amount of moisture inside to expand - This converts the hard glass into small, sponge-like kernels.
- Pumice - This is a glassy material that is formed by volcanic activity. Pumice is lightweight due to its large number of cavities produced by the expulsion of water vapor at a high temperature as lava surfaces.
- Rockwool - This is created by melting rock at a high temperature and then spinning it into fibers.
- Sand - This medium varies in composition and is usually used in conjunction with another medium.
- Vermiculite - Similar to perlite except that it has a relatively high cation exchange capacity--meaning it can hold nutrients for later use.
There are a number of other materials that can (and are) used as growing media. Hydroponic gardeners tend to be an innovative and experimental group.
