Hydroponics Growing Medium


Hydroponics Growing Medium act as an anchor to the plant so it does not fall over as it grows, provide good drainage of nutrient solution and allow the flow of oxygen to the plant roots.

Almost anything can be used as a growing medium if it meets these basic requirements:

  • It must be reasonably dense to provide enough weight and mass to anchor a plant but it cannot be too dense or it will impede the flow of oxygen and nutrient solution.
  • It must be clean and/or sterile to impede the spread of disease and pest.
  • Each individual growing medium 'nugget' must be small enough to provide a larger amount of surface area to remain damp with nutrient solution between flooding to allow the plant to feed.
  • It must be of a neutral PH (we do not want PH problems).
  • It should be easy to work with.
clay pellets as a growing medium for plants At this point you may be asking, "Why go the hydroponics route at all if I need to use a growing medium?

Why not stick with the simpler and less complex, 'tried and true' dirt gardening where soil is my growing medium?"

You could...there is certainly nothing wrong with dirt gardening except that soil always becomes packed down and too dense to be of good use.

The sad truth is that most of the fertilizer you spread around your plants is either leached or washed away.

To fertilize your dirt garden plants to the level hydroponics achieves you would have to apply a toxic amount, burning the upper roots just to feed the lower ones.

Back to growing mediums. My current favorites are Leca clay pellets and pea stone. The clay pellets are commercially made small, marble-sized balls of kiln-fired clay. They are light in weight and density, clean and very easy to work with. Because they are not very dense I use them in systems containing small containers, one per plant, where the container itself helps stop a growing plant from toppling. For this they are ideal.

peastone as a growing medium Pea stone is great for larger containers each containing several plants. It is cheap, dense and readily available. On the negative side it is extremely heavy, very dirty and could change your nutrient soultion's PH fairly quickly. Before use I rinse the pea stone by shoveling it into a wheelbarrow and hosing it down until the water runs clear (it is an exhausting job). It comes in small 40 lb. bags.

There are many excellent commercially made mediums especially designed for hydroponics all of which I would recommend.

  • Leca clay pellets - described above. Also marketed as Hydroton.
  • Hygromite - a silica based mineral rock that was kiln dried into small stone size pebbles. It is 100% organic and not too expensive but, as a downside, must be rinsed to clean the constant dust it erodes.
  • Rockwool - very popular medium made from melting igneous rock and dripping it onto a spinning disk to dry (like cotton candy). It's readily available but somewhat dirty and it produces a dust when first setting it up that cannot be something you want to breath. It also comes in grow cube form.
  • Grow Cubes - with names like Oasis, Jiffy 7 or Jiffy 9 these are made from compressed fibers of cocoa, wood, peat or rockwool just to name a few. They have excellant water retention and are used for propagating seedlings from seeds. The seedling and the entire cube can be easily dropped into a hydroponics system as is when ready. My only problem with these (and entirely my fault) was a higher incidence of 'damping-off' disease due to the fact that these cubes never dried out for me - maybe I should have cut back on my watering...
  • Coconut Coir - Coir is another relatively cheap substrate used in hydroponic gardens. Coir has a high natural salt content so should be rinsed well before use; this also prevents dry 'clots' from forming. Most coir is purchased pre-rinsed but I would rinse it again before use.
rockwool as a growing medium

(Pictured left is Rockwool). You can make your own growing medium using combinations of rocks, sand, perlite, vermiculite, peat moss, sawdust, styrofoam, paper, cardboard or anything you could possibly think of.

The key word here is to 'experiment'...

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