Hydroponics systems allow you to grow your plants with no soil. Instead you will have to replace the soil with a growing medium to anchor your plants. (read more)
It is very important to make sure that your growth medium is pH stable. If your growth medium is not pH stable, you will constantly changing the pH balance of your nutrient solution. Other adverse effects can also be cause since the grow medium is in direct contact with your plants roots. Unstable pH levels may cause your roots to be unable to absorb what they need from your nutrient solution. Almost all grow mediums that are sold specifically for hydroponics gardening are going to be pH stable, you will only have to worry about this if you choose to go with another type of medium.
The next thing to consider when selecting a grow medium is the amount of moisture that your plants will require to grow properly. Some plants require large amounts of water and cannot handle long dry spells, where other plants cannot be wet for long periods of time or they may get root rot. Because different plants have different requirements, there are many choices of growing medium for you to select from.
One of the most common choices of grow medium is Grow Rock (Hydrocorn). This lightweight clay aggregate is formed into small pebble sized rocks and super-fired to produce a porous growth medium. These rocks are heavy enough to hold your plants stable, are sterile, and will hold moisture well. Another plus to Grow Rock is that they are reusable, simply clean the rocks off, and you can use them to grow another crop.
Rock wool is a porous, non-degradable, and sterile grow medium that’s primarily composed of limestone and granite. Rock wool is made by melting these to stones down and spinning them together, much like cotton candy. This spun material is then formed and compressed into sheets, slabs, cubes, flocking, and blocks that will hold moisture without holding nutrients. One of the best parts about Rock Wool is that even when completely saturate with water, Rock Wool will hold about 20 percent air providing your plants roots with oxygen.
So lightweight that they can float are vermiculite and perlite. Superheating these two causes them to expand into low-density nuggets that absorb and retain water and nutrients very well. Both work well in drip systems, or in any system if combined with another medium to help hold them down. Being very inexpensive and easy to use make vermiculite and perlite great choices for beginning hydroponics gardeners.
For anyone that wants to go with the fully organic approach, there’s Coco Chips and Coco Fiber. Available in the consistency of potting soil and in larger sizes a lot like wood chips, that allow for better aeration of the root system. Coco chips and fiber hold much more oxygen than rock wool, but are not reusable so if you mix them with another medium it may be very difficult to separate them.