There are many different growing mediums for plants. The main requirements are that the material is capable of holding water and also has air gaps around it when it is used to fill a container. The substrate should hold the nutrient within its structure yet not be altered by it. For example in soil grown plants if the soil is allowed to become too wet it will turn into a water based suspension, a bit like mud soup. A good hydroponic substrate like clay pebbles for example will hold the moisture and allow the excess to drain away. Even when immersed in liquid the clay will still retain air gaps in between some of the balls. The main different media in common use for hydroponic gardening are:-
Rockwool. This highly popular product is produced from molten rock spun into fibres. Used in starter cubes as a media for seeds, cuttings and seedlings, it produces consistently good results. The established seedlings can then be transferred into larger cubes, with a hole to take the starter cube, and grown on. The plant, complete with its cubes and root system, can then be planted into rockwool slabs and grown to maturity. This method is widely used in commercial growing. It is important to use the correct rockwool product for each stage of growth as the differing grades have differing properties. It would be unwise, for example, to grow seedlings in a substrate that allowed them to become too wet and encouraged either root rot or fungus attack. This product can also be pH variable, so if in doubt ask your hydroponics supplier for help.
For more information about Rockwool and its applications click here.
This is currently the most popular hydroponic soil substitute on the market. Composed of shale that has been pelletized and heat treated, these inert, sterile pebbles provide excellent aeration properties. Their high water storage capacity, balanced capillary attraction, superb pH stability and the capability of being re-used makes them a real winner. The pebbles also help to provide an anchor for the plantís root system. Clay pebbles are used in ebb and flow, drip irrigation, passive and even some NFT systems. Discarded pebbles can be mixed with soil to provide an excellent aerating, and draining material for pot plants.
Perlite. Made from processed granules of volcanic rock, having excellent capillary properties and being non-compacting, all of which makes for good aeration, Perlite mediums have been used for many years in pot culture or with drippers. A lightweight material, it is very suitable for growing from seed to maturity.
Vermiculite. Made from heat treated Mica, a natural mineral, vermiculite is used in a variety if industries. It is an excellent insulation material which helps to keep roots at an even temperature, which is ideal for seeds and clones or cuttings. Used alone it can hold too much water, making it one of the unsuitable mediums for potting, unless mixed with Perlite or a similar substrate to reduce the water retention.
Coco Coir Fibre. This substrate is made from coconut husks. These are treated either chemically or by weathering for about 18 months, to remove the salt and other impurities. Coir is a coarse fibrous material which lends itself to potting and gives a light aerating environment for your plants. It is usually sold in 50kg bags, or in pre-formed slabs. Coco Coir Fibre mediums should always be used with Coco specific nutrients.
Spreader Matting. This is supplied in various lengths and widths. Of the various growing mediums, spreader matting is the one used in NFT systems to ensure an even distribution of nutrients. The matting is discarded after the crop has been harvested.
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