In North Dakota, indoor-grown lettuce faces water pH levels higher than the ideal 5.5 to 6.5 range, with Fargo's water averaging a pH of 9.2 from 2018 to 2022. Addressing the gap in research on high pH's impact on lettuce, this study, running from 2023 to 2024, explored the effects of pH levels on the yield of lettuce grown in deep water culture (DWC) hydroponic systems. We tested three lettuce varieties (Casey, Gladius, and Tendita) under four pH conditions (6.3, 7.0, 8.3, and an unbuffered level), with each setup replicated four times. Th initial growth was in rock wool cubes under a clear dome for a month before transferring to DWC for another month. The results indicated significant differences in yield and size across pH levels and varieties. Gladius yielded the highest at pH 6.3 (86.0 g/plant), while Casey showed the lowest yield at pH 7.0 (9.6 g/plant). Gladius also achieved the largest diameter (25.1 cm) at pH 6.3, contrasting with Casey's smallest at 7.0 pH (10.2 cm). Notably, high pH (8.3) still produced reasonable yields and sizes, especially with the Gladius variety, highlighting the potential for selecting suitable varieties to mitigate adverse pH effects. This study underscores the importance of variety selection in hydroponic systems with non-ideal water pH, providing crucial insights for optimizing indoor lettuce production.
