Potatoes (Solanum tuberosum L.) have been grown successfully with a recirculating nutrient film technique (NFT) when a fresh nutrient solution is used for each planting. During the past year, we conducted two studies in which the same nutrient solution was used for successive plantings (EC and pH were maintained at 0.12 S·m–1 and 5.8). Results showed that successive plantings became prematurely induced (tubers initiating near 20 days after planting–DAP), causing stunted shoot growth and reduced yields per plant. When “old” nutrient solution from a continuous production system was regularly added to a newly started plant system maintained under a non-inductive environment (12-h photoperiod with night break of 6 h into dark), tubers formed on “old” nutrient solution plants (24 DAP), but not on “new” solution plants. When charcoal water filters were placed on the systems, plants grown on either “old” or “new” nutrient solutions showed no tuber initiation (plants harvested at 42 DAP). Results suggest that a tuber-inducing factor(s) emanating from the plants accumulates in the nutrient solution over time and that the factor(s) can be removed by charcoal absorption.