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.

Hydrogen peroxide has been used as a sanitation agent for many years. Recently, hydrogen peroxide products have been used to remove algae from irrigation lines and sanitize hydroponic systems between uses. However, hydrogen peroxide can have phytotoxic effects on plants at high concentrations. The goal of this research was to determine if hydrogen peroxide treatments affected plant and algae growth in the ebb and flow hydroponic systems. The research was conducted at the Department of Horticulture and Landscape Architecture greenhouses in Stillwater, OK. Two cultivars of lettuce, ‘Green Forest’ and ‘Tropicana’, and two cultivars of basil, ‘Aroma II’ and ‘Genovese’, were transplanted into the ebb and flow hydroponic systems, and three different hydrogen peroxide products, PERpose Plus, ZeroTol, and 3% hydrogen peroxide, were applied at different rates and combinations in two experiments. Shoot fresh weight in lettuce was found to be significantly greater in control and 3% hydrogen peroxide treatments for both cultivars; however, in ‘Tropicana’ those treatments were not different from any other treatment. Greater amounts of PERpose Plus and ZeroTol, such as 60 mL, restricted plant growth in lettuce, whereas only cultivar differences for SPAD and plant width were reported for basil. Algae growth was not significantly controlled by any treatment in this research based on algae counts, weights, or spectrometer readings. However, algae species quantification did show that Microspora tumidula was found in the greatest concentrations in control, with a 96.0%, 99.2%, 94.0%, and 97.9% reduction in the 15 mL ZeroTol, 60 mL ZeroTol, 15 mL PERpose Plus, and 3% hydrogen peroxide treatments, respectively. Other algae genera identified included Scenedesmus, Chlamydomonas, Gloeocystis, Tetraspora, Leptolyngbya, Pennate diatoms, and Centric diatoms.

Brussels sprouts (Brassica oleracea L. var. gemmifera) is a slow-growing, cool-season crop with a maturation time ranging from 3 to 4 mo. In areas where high temperatures can be expected the quality of sprouts is lowered. In Oklahoma, USA, growers have a narrow window to grow the crop in the spring because temperature rising to become undesirable for sprout production can occur in late spring. Variety selection is critical since some varieties may not produce firm harvestable sprouts under Oklahoma growing conditions. Eleven cultivars were included in the 2020 trial and 15 cultivars were included in the 2021 trial. Five and 13 cultivars that developed marketable sprouts were harvested in 2020 and 2021, respectively. Plant height, plant weight, and number and weight of marketable and cull sprouts were recorded. “Marte” and “Dagan” in both years, and “Confidant” in 2021 were the best performers with higher marketable yield for spring Brussels sprout production in Oklahoma. The results provide important guidance for growers to select cultivars suitable for a climate with a short period of cool temperatures.