One of a plant’s requirements is for support which is usually provided by its roots anchored in the soil. Soil is not used in hydroponic systems but there are other types of mediums which are suitable. Sand, gravel, scoria, pumice, Vermiculite, Coir, Expanded clay etc, or a mixture of these mediums can be used.
Virtually any inert material can be used provided that the material is clean, will not add any extra chemical constituents to the nutrient mix, and that it will provide good drainage. Always wash the medium well before use, and if you are in any doubt, use a weak solution of household bleach to sterilize the medium. Coarse, washed, river sand is a good medium when used with a drainage base of gravel. Gravel alone is also suitable. The best sizes to use are between 3mm and 10mm.
Gravel lasts well which is why it is used by many commercial installations. It is also easy to remove plants from gravel without leaving quantities of root material broken off in the medium where they will rot. Scoria can cause problems because small roots will grow into the scoria so it is better used for growing indoor plants which will not need frequent repotting.
Pumice, like Scoria, is a very porous medium but you will have to make sure that the pumice is free from chemical contamination. It often contains sulphur.
Vermiculite is a lightweight and very porous medium, ideal for starting off seeds and exceptional for raising cuttings in.
Vermiculite is quite expensive when compared with other products so it pays to reduce the amount you need by mixing it with other substances. Perlite is another medium which retains moisture well.
I would recommend that you try gravel as your medium with a layer of perlite or vermiculite worked into the top 40cm.
You can easily combine any of the mediums mentioned, to a degree it depends on what you have available locally. Remember your medium should provide a place where the plant’s roots can support the plant while still allowing air and the nutrient mixture through without adding any extra substances.
Worms are valuable in the garden because while dragging decaying organic matter underground they form small tunnels which allow more oxygen into the soil. That is why plants will grow well in a light, well cultivated soil. A key job is to ensure you can handle the worms
Don’t over water your plants
Plants will often die if the soil is over watered, making it heavy and cutting off the oxygen supply to the plant’s roots. All hydroponic systems therefore, have to include some way of introducing oxygen to the plant’s root structure. Keep this in mind, it is very important.
A number of different methods for bringing oxygen into hydroponic systems are described later in the post. One simple way is to use a small air pump of the type used in goldfish tanks.
The air pump is plugged into a normal power point and the plastic hose running from the pump is placed into your solution of water and nutrient elements. Air is bubbled into your nutrient mixture for the benefit of the plant’s roots in the same way as it is bubbled into an aquarium for the benefit of the goldfish.