Growing Mediums
Growing mediums provide the support system of your indoor garden. The main functions of any hydroponic medium is to anchor the roots and store water and nutrients for the plant to feed on. You want to make sure that the growing medium you use has plenty of aeration and drains well. You want to make the nutrients available to the plant, but not oversaturate the roots.
Types of Growing Mediums
The growing medium you choose depends on what type of hydroponic growing system you are using. Many systems use no medium at all because the plant's roots are suspended in air or water. Other systems work best with one of the newer growing medium mixtures. The ideal hydroponic medium for most systems will hold equal parts water and oxygen, making both available to the roots at all times. Water will always seek lowest ground and will run freely through coarse mediums only to drain out or collect at the bottom of the container. This is not a problem in a hydroponic system where the nutrient solution is constantly circulated, but it would not work in an ebb and flow system.
Clay pebbles, also called grow rock, work very well in aeroponic systems. They should be combined with a growing medium mixture when used in other types of hydroponic systems because they do not retain any water on their own.
Shredded coconut fiber is an excellent organic growing medium. It is commonly found mixed with perlite or rockwool, but can also be used effectively by itself.
Perlite is a good choice for many indoor gardening designs, especially wick hydroponic systems. It is inexpensive, does not retain much water, and is very porous. It works very well in a growing medium mixture with 50/50 vermiculite because its natural aeration will balance out the vermiculite's water retention.
Rockwool is probably the most popular growing medium used today. It is sold in cubes of varying sizes and is reusable, making it very versatile for the indoor gardener. Rockwool can hold 10 times as much water as soil but cannot be overwatered due to its airy nature. It should be pre-treated before garden use because of its natural alkaline pH.
Vermiculite, although common, can be a poor choice for a home indoor gardener. It can contain small amounts of asbestos, which is very dangerous to your health. Always wear a mask when working with vermiculite, especially in the small spaces most gardeners use. Aside from the health risk, vermiculite's great water retention ability makes it an effective growing medium.