Growing Mediums and Hydroponics
Growing Medium is used in place of the soil in a hydroponic system and it is generally inert. The growing medium will not be able to grow anything on its own but does help to support the plants weight as well as the roots. It's a soilless material that is porous so it can hold the moisture and oxygen that the root system requires to grow. The Growing medium doesn't supply the plant with any nutrients whatsoever, the nutrients are supplied to the plant by the nutrient solution.
There are many different materials used for a growing medium but the most common types are Rockwool, Lightweight Expanded Clay Aggregate (called, Hydrocorn or Grow Rock), Perlite and Coconut Fiber/Coconut chips. We have even seen hay bails used as growing medium to grow tomatoes using a non recovery (nutrients are not recirculated back) drip system supplying the nutrients.
Some systems don't use a growing medium at all, or just enough to get seeds started then their placed into the system. Water couture systems employ this technic quite often. This is where the plants are placed in/on a floating material (usually Styrofoam). This floats on top of the nutrient solution and the roots grow through the bottom of it into the nutrient solution. With no waist this can be quite cost effective, especially for larger Hydroponic operations.
Rockwool is a fairly recent addition to the types of growing mediums available on the market. This sterile, porous, non degradable medium is composed primarily of granite or limestone which is melted and spun like cotton candy. Rockwool is then formed into blocks, sheets, cubes, slabs, or flocking. Rockwool absorbs moisture without holding nutrients, and even when it is completely saturated still retains 20% air for your root system.
Grow Rock (Hydrocorn)
Grow rock is a Lightweight Expanded Clay Aggregate stone (L.E.C.A.) that is a type of clay which is super-fired to create a porous medium. It is also heavy enough to provide secure support for your plants' root systems. This non-degradable, sterile growing medium holds moisture, has a neutral pH, and also will wick nutrient solution to the root systems of your plants. Hydrocorn is also recyclable, it can be cleaned, serialized then reused again. Although in large scale growing operations this can be time consuming. Grow rock is often the growing medium of choice of novices and professionals alike because it is easy to use.
Coco Fiber Coco Chips
An alternative to using rockwool, Coconut fiber is the first "organic" medium to offer high performance in modern hydroponic applications. Coconut fiber can also be added into soil mixtures to increase water holding capacity. Coconut fiber holds more oxygen than rockwool and is pH neutral. Available as compressed bricks, when Coconut fiber is soaked in water it expands to 6 times its compressed size. Many growers have found that a 50/50 mix of coconut fiber and L.E.C.A is the perfect organic medium. Coconut chips are the same thing but are in chunks so they don't fall through the openings in the growing baskets the way coco fiber can.
Perlite is primarily composed of minerals subjected to intense heat which then expand and become very absorbent. This material is light, has a neutral pH, excellent wicking action, and is very porous. Perlite is used in a wide variety of hydroponic systems because of its ability to hold moisture and nutrients as well as air. Perlite is widely used because of it's ability to hold moisture and nutrients, it's also easy to use and inexpensive. But because perlite is so light, it tends to float to the top of the water and when used all by itself in some situations perlite may not be able to support the plants weight because of its floating ability. Though when added to other growing mediums, it adds these benefits and can still support the plants weight.
Vermiculite Similar to perlite except that it has a relatively high cation exchange capacity--meaning it can hold nutrients for later use. Also like the perlite, vermiculite is very light and tends to float. So it may not be the best choice to use in EBB and Flow (Flood and Drain) systems unless mixed with another growing medium. Although, they are quite suited for drip systems.