Nutrient film technique relies on a flow of nutrient enriched water flowing past the plant roots. This is typically taken from a tank and recycled, although can also be a "run to waste" system. (This less popular arrangement sounds wasteful and expensive. Although lower concentrations of nutrient are used, it has fallen from popularity.) Plant roots grow on the flat surface and the plant is supported by the (reflective) white covering, which can be cut to accomodate any plant. A pump is required to circulate the nutrient during the period of light, which may be up to 18 hours per day, or reduced to simulate autumn harvest. The pump can run permanently, although plants only grow when they receive energy in the form of light, therefore nutrient received during night is not utilised and merely encourages algae. NFT is ideal for greenhouse use, although NFT systems in general require higher maintainance than flood and drain systems. Excellent results can be obtained, although it requires more practice and experience to achieve success.