Nutrient solution temperature in a hydroponic system affects °Brix and yield of lettuce; thus, it is important to maintain the water temperature within an appropriate range. Nutrient-film technique (NFT) trials were conducted to investigate the effects of different water temperatures (18.3 °C, 21.1 °C, and ambient) on growth and °Brix of 17 cultivars from five different types (Loose leaf, Romaine, Butterhead, Salanova, and Batavian) of lettuce. The average daily water temperature for ambient treatment was recorded to be 20 to 26.5 °C. The study was conducted in a split-plot design with three replications over time. Results indicated that water temperature affected root and shoot fresh and dry weight, plant width, and °Brix for lettuce. Lettuce grown at 21.1 °C were 15% greater for shoot fresh weight than plants grown at ambient conditions. All the growth and quality parameters of lettuce were found to be affected by cultivars, with “Coastal Star” showing the best results in both growth and °Brix parameters. All the cultivars of the Romaine type showed greater growth and °Brix, while Salanova lettuce did not perform well in all treatments compared to other lettuce types. For CO₂ assimilation, the interaction between water temperature and cultivars was significant, with “Parris Island” having the greatest rate at ambient water temperature. These results suggested that maintaining water temperature at 21.1 °C produced lettuce with greater growth and biomass but had 26% lower °Brix than lettuce grown at 18.3 °C.

Use of hydroponics is increasing because of its ability to be used for year round vegetable production using an environmentally sustainable system. Management of solution pH is an important challenge in hydroponics systems. Our objective was to quantify the effects of various pH modifiers on growth and nutrient uptake of leafy greens and stability of nutrient solution’s pH. Lettuce, basil, and Swiss chard were transplanted into an Ebb and flow system, and nutrient solution pH was maintained using three different pH modifiers (pH Down, lime juice, or vinegar). The nutrient solution’s pH was maintained between 5.5 and 6.5. pH Down resulted in the most stable solution pH and required the least amount of product used when compared to lime juice and vinegar. The cost of using phosphoric acid or lime juice was greater than that of using vinegar. Vinegar reduced the yield of all crops in comparison to pH Down. When compared to pH Down, lime juice reduced the yield of basil and Swiss chard but not that of lettuce. Therefore, growers can use lime juice as an alternative to pH Down in lettuce production but not for basil and Swiss chard, while vinegar would not be recommended for any of the crops studied.

Carbon dioxide (CO₂) concentration is reported to be the most important climate variable in greenhouse production with its effect on plant photosynthetic assimilation. A greenhouse study was conducted using a nutrient film technique (NFT) system to quantify the effect of two different levels of CO₂ (supplemented at an average of 800 ppm and ambient at ~410 ppm) on growth and nutritional quality of basil (Ocimum basilicum L.) ‘Cardinal’, lettuce (Lactuca sativa L.) ‘Auvona’, and Swiss chard (Beta vulgaris L.) ‘Magenta Sunset’ cultivars. Two identical greenhouses were used: one with CO₂ supplementation and the other serving as the control with an ambient CO₂ concentration. The results indicate that supplemented CO₂ could significantly increase the height and width of hydroponically grown leafy greens. Supplemented CO₂ increased the fresh weight of basil ‘Cardinal’, lettuce ‘Auvona’, and Swiss chard ‘Magenta Sunset’ by 29%, 24.7%, and 39.5%, respectively, and dry weight by 34.4%, 21.4%, and 40.1%, respectively. These results correspond to a significant reduction in Soil Plant Analysis Development (SPAD) and atLEAF values, which represent a decrease in leaf chlorophyll content under supplemented CO₂ conditions. Chlorophyll, nitrogen (N), phosphorus (P), and magnesium (Mg) concentrations were generally lower in plants grown in supplemented CO₂ conditions, but the results were not consistent for each species. Supplemented CO₂ reduced tissue N concentration for basil ‘Cardinal’ and lettuce ‘Auvona’ but not Swiss chard, while Mg concentration was reduced in supplemented CO₂ for Swiss chard ‘Magenta Sunset’ only. In contrast, Fe concentration was increased under supplemented CO₂ for basil ‘Cardinal’ only. These findings suggest CO₂ supplementation could increase yield of leafy greens grown with hydroponics and have varying impact on different mineral concentrations among species.

Chlorophyll meters are used for non-destructive estimation of leaf nitrogen (N). The objective of this study was to evaluate the readings with several chlorophyll meters (SPAD-502, atLEAF, and CCM-300), different sampling sites on leaves, number of leaves used for sampling, and different types of leaf N sampling on estimation of N in leaves of potted poinsettia (Euphorbia pulcherrima) “Prestige Red.” Results showed that all meters gave readings that were correlated for N determination and also were correlated with each other. SPAD and atLEAF showed interaction between different N treatments and different sampling sites on the leaves, while CCM readings were affected by different sampling sites on the leaf. atLEAF readings showed interaction between number of leaves sampled and different N treatments. Thus, during sensor-based leaf N estimation, sampling site on leaf, number of leaves sampled, and stage of plant development should be considered to minimize error.