Hydroponic growing systems have one major advantage over traditional soil based farming and gardening - plants grown hydroponically will grow at a much faster rate than soil based plants, 30 to 50% faster on average. The overall yield of the plant will be significantly higher also. This is largely achieved due to a few different factors; the nutrients in a hydroponic system are mixed in with water and fed directly to the plants roots (as opposed to traditional soil where a root system would have to "search" for nutrients in the soil), hydroponically grown plants require very little energy to attain and break down food, and most importantly, hydroponics can utilize extra oxygen by way of the growing mediums used. So, what is the most effective growing medium for hydroponics? Rockwool. Not familiar? Read on.

Rockwool actually started off as an insulating material that was primarily used in the construction industry. Its properties were soon utilized for growing purposes and soon after that, dedicated, horticulture grade Rockwool was made available in small blocks specifically for substrate* (See below) growing systems (regular, construction grade Rockwool is more like fiberglass when used for its originally intended purpose. It was once known as "mineral insulation"). Since Rockwool holds 10 times as much water as soil and also retains 20 percent air it can be used in just about any hydroponic system very successfully.

The efficiency and superiority of Rockwool is due to a number of reasons related to its composition. It is made from volcanic rock and limestone. These elements are essentially melted together at very high temperatures (2500F) and then carefully poured over a rotating cylinder which in turn produces dense fibers (*if you've ever watched cotton candy being made, Rockwool manufacturing is very similar). After the spinning is complete and the fibers have been produced, a binding agent is introduced to the procedure. It is then pressed or poured into cubes or sheets. Try to avoid using Rockwool that is made from left over smelt as it will invariably contain higher amounts of minerals, which can lead to a poor reaction with plant fertilizers.

Since Rockwool contains a fair amount of mineral oil (a natural water repellent), it is important to seek out high quality Rockwool that has had most of the water removed during manufacture and has also had a wetting agent added to the mineral mix. As an alternative to adding a wetting agent, some manufacturers will simply coat the blocks in a surfactant which will aid in retaining water. Using surfactant treated Rockwool will mean that you will have to regularly add a wetting agent or it will simply be washed out. It is worth your while to try out different brands and see what provides the best results before investing in enough to supply your entire system.

The use of Rockwool in hydroponic substrate systems for vine crop and cut flower production has been proven many times worldwide. In North America the trend is continuing toward growing on substrates. Ease of handling, labor savings, better control over nutrition and better disease management are all reasons for this trend. These factors all point to more yield at lower cost. And that's good news for any gardener!

Future articles will focus on how to use Rockwool sheets or cubes correctly.

*A substrate growing system is a hydroponic system where the root zone is physically supported by growing media (such as Rockwool). The plants are fed by applying nutrient solution to the media. Almost any material that supports the root system, other than regular soil, is considered a useful substrate. Substrates can be organic such as peat, pine bark, sawdust etc. They can also be petroleum based such as polymeric foams or plastic beads or they can be inorganic mineral based as are sand, gravel, perlite and Rockwool.