What makes hydroponic systems different from traditional in-ground gardening is a soil-less growing medium. No dirt! All plants require support, to be held up. This basic requirement is dealt with by soil-less growing mediums which are inert, mostly non-organic materials. Non- organic refers to the medium not being derived from living organisms (unlike soil- which is). There is a perplexing jumble of growing mediums available. Generally speaking, these mediums are porous, light, and coarse, allowing oxygen and nutrients easy access to the plants roots. Some of the most common are:
This is produced from the husk that surrounds the coconut shell. Made up of millions of tiny micro-sponges, it can absorb and hold up to eight times its weight in water. It lasting three times as long as peat moss so is fairly sturdy. It is also called palm peat, coco, or just coir. Some of the advantages are better water retention and aeration. The disadvantages of coconut coir are its breakdown after several uses and some drainage issues. It is often mixed with other media to improve drainage in hydroponic systems.
L.E.C.A / Lightweight Expanded Clay Aggregate
This is clay which has been heated under high temperatures until it puffs up. It makes a very coarse medium as the clay balls are about 1/4" across. Superb drainage, holds moisture, stays put and is reusable after sterilization are just some of the advantages of this medium. On the downside it doesn’t hold moisture as well as mediums like coconut coir and can be more costly.
Glass flakes (Silica) are heated until it expands producing what we know as perlite. These tiny nodules hold water well and provide drainage. A common medium due to its low density (have you ever picked up a large bag of Perlite – it weighs almost nothing) and somewhat low cost. Its advantages are its reusability and low cost, not to mentioning it’s lightweight. That being said it cannot be used alone for ebb & flow hydroponic systems, it will float away or move during flooding cycles.
Fibers spun from melted Basaltic rock. A binder is added to the fibers and they are compressed and cured into large slabs. The density of this growing medium can be adjusted by changes in the amount of pressure during production. Large slabs are cut into smaller slabs and propagation blocks for easy handling. Advantages of this medium are the ease of handling, convenience, better control over nutrition, being able to plant seeds in it and allow the plants to be very stable. The drawbacks are that all rockwool is not the same. Some are produced from slag left over from smelting operations and as such have a high proportion of metals which can be somewhat reactive with your nutrient solutions. Rockwool can also have mineral oils present and may contain wetting agents used to counteract this that will wash out over time.
Much more information regarding these mediums is available from other sources, this basic summary of common growing mediums used by hydroponic systems touches lightly on the subject. Vive la difference!Check out more information about hydroponics systems or in home gardens at my website. It's a site dedicated to hydroponics