Growing systems that recirculate the nutrient solution are attractive, because they couple saving of water and fertilizers with decreased leaching. However, the longer irrigation water is collected and re-used, the higher the concentration of salts. Maintaining the EC of the nutrient solution within (conservative) boundaries requires flushing rates of 30␘r more, in spite of the recirculating facilities. In order to determine the processes responsible for the reduction of fresh yield, that is often the consequence of growth under salinity stress, we investigated the effect on vegetative growth of a tomato crop, of high EC in combination with two water uptake rates. Associated yield and yield quality data are presented in the second paper of this series. Climate in two identical glasshouses was controlled to maintain a constant ratio (65€of potential evaporation, while preserving equal assimilation levels. Half of the rows in each house were given a 2 dS/m treatment in the root medium whereas the other half were given 10 dS/m. Leaf growth, canopy development and fresh and dry yield were traced during a whole spring growing season. No effect of the climate treatment could be detected in leaf area or leaf shape. High salinity, on the other hand, reduced total leaf area by ca. 15°through a prompt reduction of leaf expansion. Reduction in light interception was smaller, so that there was no detectable cut back of dry matter accumulation in the fruits.