Perlite

Perlite is a processed mineral. It has excellent water holding properties but is less spongy and better drained than vermiculite (read Vermiculite). Perlite is made from a volcanic rock treated at very high temperatures to form sponge like balls. Perlite is often used by itself or in a 70/30 mix to add a little more moisture to your growing media. Perlite is white in colour, which causes algae to grow quite easily in perlite, while this does not harm your plants it can clog your hoses ia recirculating system.

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Expanded Clay

Expanded Clay is made by baking specially prepared clay in ovens at around 1200 degrees Celsius. The clay expands and the final product is hard but porous and allows good entry of both water and oxygen.

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Vermiculite

Much like perlite, vermiculite is prepared by high temperature treatment of the mineral mica, which contains silicates of aluminium and iron. It expands into very soft glittering particles, which can retain some 50% by volume. Most gardeners are familiar with the shiny golden appearance of vermiculite as it is often used in seedling bought at nurseries. The disadvantages of vermiculite is that it tends to break down over a year, which could cause your hoses and filters to clog. 

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Rockwool

Rockwool is manufactured by heating a mixture of basalt rock, limestone and silica to 1600 degrees Celsius. The molten slag is poured onto fast spinning wheels which throw the material out as fibres. As the fibres are formed the are sprayed with binders and wetting agents and then cured in an oven. The yellow rockwool emerges from the oven compressed into rigid slabs. It is inorganic, sterile, inert and won't bind any chemicals to its structure. Rockwool also has an extraordinary high water and air holding capacity as it takes up to 80% water and 20% air. The biggest disadvantage is that it holds so much water, so it is essential to have good drainage, if not your plants will slowly drown.  

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Coco Coir

Coco Coir is made from the fibrous husks of ripe coconuts. It is an organic product that is free of chemical additives, harmful viruses or soil diseases. It holds 8 to 9 times it weight in water and more air than the finest granulated rockwool, it also contains naturally occurring rooting hormones and some antifungal compounds to help the coconut to survive and propagate in those competitive tropical coditions. It comes in a compressed slab which you simply submerse in water until the slab expands.  

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Last modified: April 20, 2005