This research aims to evaluate the effect of the potassium–nitrogen balance on strawberry productivity and quality parameters in soilless conditions. A trial was conducted at the Agronomic and Veterinary Hassan II Institute glasshouse in Rabat, during the 2018–2019 crop year. The pot experiment began on November 13 using three different strawberry cultivars: Fortuna, San Andreas and Sabrina. Three nutrient solutions were tested by increasing the potassium–nitrogen balance during the growth stage and decreasing it during the fruit-production stage: S1 (1.3/2.0), S2 (2.6/1.0) and S3 (3.0/0.6). For all treatments, the total dose of fertilizing elements N, P, K, Ca and Mg was identical. The experimental design was a randomized complete block with three replications. The results show that strawberry plants receiving a nutrient solution with a high K:N balance during the growth period and a low balance during the production period present the higher growth and fruit levels. Moreover, the nutrient solution with the 2.6/1.0 balance significantly increased the chlorophyll index by 8%, yield by 30% (7.9 t ha−1), total soluble solids and dry matter content by 14% and 15%, respectively, and improved taste and fruit shelf-life by 10% and 19%, respectively.