This is a method where plants are grown on a material that holds some water but has many air spaces, such as vermiculite, perlite, fibreglass or coarse sand. The water with nutrients is controlled by a timer and the amount of irrigation will depend on several factors such as temperature, the size of the plants, the type of material the plants are growing in and other more technical things. The water runs to a collecting container after irrigating the plants and may be used again or discarded. This system is used very widely for growing commercial crops of vegetables such as tomatoes and cucumbers.