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Grow Mediums

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The practice of hydroponics allows crops to be grown without the use of soil, but that doesn’t mean that the plants are to be suspended in mid-air! Alternative substances must be used to provide root support, water supply, and other functions which would usually be imparted by soil, while dispensing with the inconveniences. These substances are known as grow mediums. Let’s consider a few of the hydroponic grow mediums available, with their advantages and uses.

Rockwool and Perlite

These two have been described as the industry standards of hydroponic grow mediums. Mineral wools are created by melting rock until if reaches a treacle-like consistency, then drawing out fibres which quickly cool, resulting in a fleece-like fibrous substance. Besides its use in the hydroponics industry, mineral wool has been used as a thermal and acoustic insulator, and also in industrial filters.

Many professional hydroponics companies prefer a rockwool growing medium as its consistency allows for an optimum oxygen/water balance. The texture of this growing medium provides what many see as an ideal balance between three critical properties of any hydroponic substrate: breathability (to allow air in), permeability (for retention of fluid) and a consistency which allows the roots of the plants to anchor themselves firmly and grow freely.

Perlite is a mineral wool created from volcanic rock, and is lighter and less dense than most rockwool. It is good for use with wicking hydroponics systems, where water and nutrients are drawn up through the substrate by capillary action. Experienced enthusiasts and professionals may use perlite as a hydro grow medium, that is, for minimalist systems which use very little substrate and where all variables are directly controlled by the operator. This kind of setup can yield exceptional results with careful monitoring and regulation. Less experienced hobbyists may prefer a denser growing medium, which takes a lot of the hard work out of the process. Another consideration is that perlite dust is harmful, so it must be handled very carefully.

Expanded Clay Pebbles

Clay pebbles are one of our most popular supplementary media due to the unequalled root support they provide. Heating fragments of clay to over one thousand degrees converts it into a light weight, highly porous medium which allows both air and water to pass through and boasts excellent drainage properties. They are totally inert, are easily colonized by beneficial bacteria, and can be washed and reused after each crop.

Coco for Grow Mediums

‘Grow medium coco’ or ‘hydro coco’ are names given to coconut fibre which is used as a grow medium, or as part of mixed grow mediums UK experts recommend for organic hydroponics systems. Once again, water and oxygen capacities are critical and coconut fibre scores excellently in both these areas. Aside from its completely organic nature, ecologically conscious growers may prefer it to rockwool as the latter never fully breaks down after disposal. Coconut fibre, of course is fully compostable. Additionally, high quality hydro coco contains only minimal levels of native nutrients, and is therefore suitable as a grow medium with mixed nutrients solutions in mind.


Not a growing medium, but an all natural additive which can increase the size and number of flowers and fruit, and enhance the taste of your produce. Animal waste -based fertilizers have been common agricultural practice for centuries, so this product, famously made from bat droppings, has a strong heritage at which we should not turn up our noses.