The answer to this question depends a lot on the crop that is being grown. Substrates have been successfully employed in the cultivation of most vegetable vine crops grown in the greenhouse such as tomatoes, cucumbers, peppers, and some cut flowers such as roses and gerberas. Let us consider the advantages for using substrates with these crops.
The primary reason for using rockwool, or any substrate, in a hydroponic growing system, is to provide a buffering reservoir of nutrient solution in the root zone while maintaining an adequate volume of air (oxygen) in contact with the roots. In an NFT or other “pure” hydroponic system, the watering and feeding of the plants depend solely upon the flow of nutrient solution past the roots. If this is interrupted, for even. a short time, the plant will die. On the contrary, if the root zone is flooded the roots will suffer from a lack of oxygen. In a substrate system, the substrate maintains a reservoir of nutrient solution in the root zone along with a percentage of air pore space. This reservoir of nutrient solution is available even when the irrigation system is off for periods of time. In fact, in a substrate system irrigations are pulsed to help maintain the proper ratio of air to water.
The reservoir of nutrient solution that the substrate provides also increases the time it takes to change conditions in the root zone. Thus, the grower loses some of the immediate control over conditions in the root zone that an NFT type system would offer. The key is to use a substrate that offers the safety provided by a reservoir of nutrients, water, and air that also will respond rapidly to changes in the feed made by the grower. For example, in a rockwool system changes made by the grower are fully manifested in the root zone in 12 to 24 hours. This varies from substrate to substrate and will be discussed later.
