Since soil is not used in hydroponic systems other mediums are needed for flowers, herbs or vegetables to grow and stabilise their root system. These cultivating platforms need to be inert to ensure that they will not have an effect on the nutrients within the water solution. These kinds of substrates also need to be pH neutral, have good fluid retention but still have space for air circulation and above all be sturdy enough to hold and support the plant. You will find many forms of mediums on the marketplace and the one that you choose will be determined by the kinds of fruits and vegetables you are trying to grow. Just about any hydroponic supplier will be able to advise on what mediums to use, but here is an outline of the most common substrates used in hydroponic systems.
Perlite
Is a type of volcanic rock made up of silica and commonly created by the hydration of obsidian. Perlite comes in assorted sizes subject to what you are growing. It is generally chosen to grow cuttings in and subsequently when the crops have developed to a particular size they may need another substrate to expand in based on the type of hydroponic process you are employing.
Advantages
� Low price and reduced density material.
� Features good water retaining properties superb for potted plant life.
� Offers great drainage properties and mixes nicely with heavier substrates.
� Suitable for establishing cuttings or seeds in.
Disadvantages
� Not appropriate for ebb and flow systems as a result of its low density it may shift or drift away in the course of the flow cycles.
� Not ideal for bigger more dense crops since it cannot anchor the plants roots successfully.
Coconut Coir / Coco / Palm Peat
As the name suggests Coco is a product of coconuts, with all the husk of the coconut being used after the coconut fruit has been cut off. It is cured to produce a kind of peat that is typically sold in brick form. It is a great supplement to hydroponic systems as it expands when water is added with about 6-8 times its initial size. It is strong enough for bigger plants and lasts considerably longer than traditional peat. Furthermore it is often employed as a type of soil although it does not have the nutrients that soil has, yet it does provide you with a good structure in which crops can develop roots.
Advantages
� Excellent water retention but also allows air to circulate to the plants.
� Cheap, environmentally friendly source so good to the pocket and to the planet.
� Can be combined well with other mediums, for instance perlite to increase drainage of water.
� Has organic anti-fungal properties which aid to minimize imperfections in crops.
� Has comparable characteristics to traditional soil.
Disadvantages
� As stated above drainage is not as good as some other mediums yet can be combined to decrease this problem.
� Can just be used a limited number of times, but if you are swapping your crop type in the hydroponic system it is a good idea to replace your growing medium as well.
� Not completely effective in ebb and flow systems as a little of the product can be washed away during the flow cycles. But is appropriate for drip systems.
Clay Balls / Leca
These are small balls made out of clay that have been fired to maintain their structure. They provide no nutrient value, are inert and have a neutral pH reading. These are excellent features to have in a medium as they do not hinder the nutrients added to the system. Due to these properties they are very popular with hydroponic growers.
Advantages
� Can be purchased in a variety of sizes so are good for larger denser plants to provide good anchorage of roots.
� Can be washed and reused using white vinegar, chlorine or hydrogen peroxide solutions. Many hydroponic suppliers have washing solutions in store. However they need to be entirely rinsed after washing or this can affect the plants in the next grow.
� Inexpensive to buy and produce from a natural occurring substance.
� Have great drainage properties.
� Light-weight to use but will not float away so can be employed in ebb and flow systems.
� Retains moisture well.
� Can be blended with other substrates to increase drainage for instance coco.
Disadvantages
� Even though they can be washed it often not advised as root growth can infiltrate the clay balls. This can be seen upon splitting open the balls after use. This root development could impact future hydroponic grows.
� Does not hold water as well as coco peat but as mentioned above this can be limited by combining the two mediums.
Rock wool
Rock wool is also a favourite medium amongst hydroponic growers. It is a man-made product composed of rock that has been broken down into its mineral compounds and then spun to create rock fibres. It is typically bought in brick or slab form and has a consistency similar to those of fibreglass. It is often used in small cubes to start off seeds or cuttings and facilitates the new roots to anchor firmly onto the medium.
Advantages
� Properly treated and manufactured rock wool will be inert and as a result should not interact with other nutrients added to the hydroponic system.
� Great at retaining water required for plant growth.
� Good drainage benefits.
� Easy for plants to take up nutrients and even provides some air circulation.
� Keeps structure over extended amounts of time.
� Can be used again if washed although this is not usually advised.
Disadvantages
� Some poorer quality rock wools are produced from slag which can have a greater metal content. This can affect the pH of the wool and therefore impact on the nutrient intake by the plant.
� It is a man-made substance and subsequently not as environmentally friendly as other mediums. It is more complicated to get rid of and if placed and buried in land fill will not break down for long periods of time.
� As it has similar properties to fibre glass it can be carcinogenic, because the fibres can get into the lungs and might produce problems. It is recommended that you use a mask when originally setting up the rock wool within your system. The inclusion of water will cut down on the fibre problem as they will be less likely to become airborne.