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Does a vitamin C spray boost vitamin C in lettuce?
Spraying lettuce with vitamin C just before harvest sounds like an easy way to make it more nutritious. In two Texas Tech University greenhouse trials with hydroponic lettuce, it did not work: vitamin C in the leaves did not rise significantly at any spray strength tested.
Lettuce is quick to grow and eaten fresh, which is why the team saw it as a good crop to boost with vitamin C. Researchers at Texas Tech University in Lubbock sprayed ‘Salanova’ lettuce growing in deep-water culture with ascorbic acid (vitamin C) two and four days before harvest, to see whether the vitamin would build up in the leaves (Stubbs et al., 2026).
What this means for your grow
Nothing to try yet. In this trial, late vitamin C sprays did not make the lettuce richer in vitamin C, though they did not harm growth either. The authors found that the growing environment strongly influenced the results: across both trials, vitamin C was positively correlated with light and negatively with temperature and relative humidity. These results come from one lettuce cultivar in one greenhouse in Texas, over two seasons.
What did the team do?
Deep-water culture is a hydroponic system where the roots hang in a continuously aerated nutrient solution. The team ran two trials in deep-water units at the Texas Tech University Gardens and Greenhouse Complex, one from October to November 2024 and one from March to May 2025. Seedlings were started in rockwool cubes and moved into net pots once they had their first true leaf.
Near harvest, plants were sprayed with ascorbic acid dissolved in water at sunset, four days and two days before harvest, until the leaves were soaked and dripping. The first trial compared 0, 500, 750 and 1000 ppm. Because few effects showed up, the second trial dropped 750 ppm and added a stronger 2500 ppm spray.
The team tracked plant size and weight, leaf nutrients, leaf pigments, proline (a compound plants often build up under stress), phenolics, flavonoids, and vitamin C in total and in its reduced form. Temperature, humidity and light were logged every hour.
What did they find?
- No vitamin C boost. Total and reduced vitamin C did not differ significantly between spray strengths in either trial. In trial 1, total vitamin C ranged from 18.59 to 21.30 mg per 100 g of fresh leaf; in trial 2, from 4.06 to 6.90 mg per 100 g.
- No harm to growth. Plant width, chlorophyll readings, fresh weight and dry weight were statistically similar across all spray strengths in both trials.
- Some small changes in the first trial only. In trial 1, several leaf nutrients (nitrogen, calcium, sulfur, boron, iron and copper) rose with stronger sprays, while manganese was lower at 1000 ppm. Proline was highest at 750 and 1000 ppm. None of these differences appeared in trial 2.
- No change in phenolics or flavonoids. Neither differed significantly between treatments in either trial.
- The weather inside the greenhouse mattered. Trial 1 had steadier temperatures and, in general, higher vitamin C than trial 2. Trial 2 swung from 5.5 °C to 33.2 °C. Vitamin C was positively correlated with light and negatively with temperature and relative humidity.
What could it mean?
The authors conclude that foliar ascorbic acid did not consistently raise vitamin C under the conditions tested, but that the concentrations used were physiologically safe for ‘Salanova’ lettuce. They think the late timing explains why growth was unaffected, and that heat and unstable conditions may have broken down the applied vitamin C. They suggest future work try repeated sprays through the growth cycle, stronger concentrations, other growth stages, or fully controlled plant factories with artificial lighting. For now this is a question for researchers, not something ready to try at home.
What were the limitations?
- The trials ran in a greenhouse rather than a fully controlled environment, and the authors say environmental variability, especially the wider temperature swings in trial 2, masked most treatment effects.
- Sprays were applied only 2 and 4 days before harvest, after most growth had already occurred.
- The two trials differed significantly from each other, so they were analysed separately. They also ran in different seasons and for different lengths (4 and 7 weeks).
Trial details
- Where: United States. Texas Tech University Gardens and Greenhouse Complex, Lubbock, Texas (lat. 33.584022N, long. −101.886972W); greenhouse.
- When: trial 1 from 15 October to 22 November 2024; trial 2 from 25 March to 16 May 2025. Plants grown 4 weeks (trial 1) and 7 weeks (trial 2) before harvest.
- Crop: lettuce (Lactuca sativa) ‘Salanova’, started in rockwool cubes and transplanted at the first true-leaf stage.
- System: deep-water culture units, each a reservoir of about 27 L of nutrient solution with an air stone bubbler, a lid and net pots, six plants per unit. The solution was changed at week 2.
- Nutrition: reverse-osmosis water with Maxigro fertiliser (10-5-14 NPK; General Hydroponics) at 125 ppm N; pH about 6 ± 0.5; EC about 1.3 dS·m−1.
- Lighting: supplemental lighting for 14 hours a day, averaging 163.48 µmol·m−2·s−1 in trial 1 and 181.28 µmol·m−2·s−1 in trial 2; light levels ranged from 1.2 to 573.7 and from 1.2 to 641.2 µmol·m−2·s−1.
- Climate: trial 1 averaged 23.7 °C (18.1 to 29.1 °C) and 43.1% relative humidity (17.9% to 81.6%); trial 2 averaged 21.6 °C (5.5 to 33.2 °C) and 52.0% relative humidity (10.3% to 92.5%).
- Treatments: foliar ascorbic acid at 0, 500, 750 and 1000 ppm (trial 1) and 0, 500, 1000 and 2500 ppm (trial 2), sprayed at sunset 4 and 2 days before harvest until leaves dripped; about 600 mL of solution per treatment.
- Design: randomised block design; five deep-water units per treatment (20 units, 120 plants per trial); two plants chosen at random from each unit, 10 plants per treatment, were analysed. ANOVA, significance at P < 0.05, in JMP Student Edition v. 19; trials analysed separately.
- Results: total vitamin C 18.59 to 21.30 mg/100 g fresh matter (trial 1) and 4.06 to 6.90 mg/100 g (trial 2); reduced vitamin C 6.36 to 8.11 and 2.33 to 3.62 mg/100 g; none significantly different between treatments. Fresh weight 37.0 to 48.4 g (trial 1) and 130.6 to 147.9 g (trial 2), not significantly different. Trial 1 proline highest at 750 and 1000 ppm (3.608 and 3.732 µmol·g−1 dry weight; P = 0.0041); chlorophyll a highest at 500 ppm (P = 0.038).
- Other statements: the authors say they used Grammarly and Copilot to improve grammar and clarity and to identify relevant articles, then reviewed and edited the content.
- Publication: HortScience 61(12): 2595-2603, published online 30 October 2026, https://doi.org/10.21273/HORTSCI19692-26. Licence: CC BY-NC 4.0.
- Not reported in the paper: the type of supplemental light, its spectrum and the daily light integral, CO2, funding, and conflicts of interest.
Links
- The study: Vitamin C Biofortification of Lettuce (Lactuca sativa ‘Salanova’) in a Deep-water Culture System
- The institution: Department of Plant and Soil Science, Texas Tech University
References
- Stubbs, K., Regmi, A., Vargas, K., Singh, S., Thompson, L., & Simpson, C. (2026). Vitamin C biofortification of lettuce (Lactuca sativa ‘Salanova’) in a deep-water culture system. HortScience, 61(12), 2595-2603. https://doi.org/10.21273/HORTSCI19692-26