Throughout the European Union the use of closed growing systems in greenhouses is seen as an alternative to free drainage systems. In preparation to it a project was initiated at several European universities and institutes to introduce management and control systems to improve the quality of the product, the environment and the growing process. As part of this project, tests were carried out at the IMAG-DLO institute. Growing channels and a trickle irrigation system with an NFT closed growing system were used. Responses on step and impulse changes of the EC value were studied in order to establish the dynamic behaviour of the supply system. A time delay algorithm for trickle irrigation and an aggregated dead zone model for closed growing channels were developed. The layout of water supply lines was investigated. A Tichelmann layout with forced circulation was installed in the greenhouse to overcome the large time delays, which occur as a result of the dead-end in the supply tube in the current layout.