The design of a controller for water supply and nutrient application in closed growing systems is presented and discussed with reference to nutrient film techniques in a 150 msuperscript 2 greenhouse. The 'robust design' method aims to distinguish between stability and performance and, in this case, the method deals with uncertainties in the model description of the real process, i.e. variability of flow and seasonal changes. Robust performance and robust stability, as qualities of the controlled process, were shown to be feasible for the control of nutrient application in closed growing systems. Algorithm performance was tested in a simulation procedure and shows very good disturbance suppression, staying well within the pre-set 10% limits. More standard design procedures could lead to a stable controlled process but would certainly be more conservative than the robust controller presented.