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Does extra light before harvest make leafy greens heavier?
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Quick find: this post is based on the published summary (abstract) of the study, not the full paper.
Can a burst of extra light in the last few days before harvest make leafy greens heavier? In a greenhouse trial by researchers at the University of Tennessee and The Ohio State University, fresh weight generally went up the stronger the extra light and the longer it was given.
The team called it end-of-production lighting: light added for a short time just before harvest. They tested it on four hydroponic greenhouse crops, lettuce, arugula, spinach and mustard greens, because, as the authors note, crop-specific ways to use it are still needed (Friedrich et al., 2026).
What this means for your grow
If you grow leafy greens under cover, this suggests a short light boost near harvest could add weight. The heaviest plants in this trial came from the strongest extra light given for the longest, about 600 µmol per square metre per second for 7 days before harvest. The plants were grown hydroponically in a greenhouse on a 16-hour day, so it is a possibility to test, not a promise. The published summary does not say how large the gains were.
What did they test and find?
- The crops: ‘Salanova® Hydroponic Red Butter’ lettuce, ‘Astro’ arugula, ‘Space’ spinach and ‘Amara’ mustard greens (Brassica carinata).
- The light boost: 7 days, 3 days or 1 day before harvest, plants got an extra 0 (control), about 100, 200, 400 or 600 µmol per square metre per second of broad-spectrum white light, or about 200 µmol per square metre per second of red and blue light.
- Weight: across all four crops, fresh weight generally rose with stronger and longer extra light, and was greatest at about 600 µmol per square metre per second given for 7 days.
- Photosystem II efficiency: the response varied by crop. It was generally lower when the light was raised 1 or 3 days before harvest, and recovered when it was raised 3 or 7 days before harvest.
- Looks after harvest: the visual quality of lettuce, spinach and mustard greens was largely unaffected. Arugula looked better a week after harvest the longer it had been given the broad-spectrum light.
Trial details
- Who: Plant Sciences Department, University of Tennessee, and Department of Horticulture and Crop Science, The Ohio State University, USA.
- Where: a greenhouse (hydroponic production).
- Crops: lettuce (Lactuca sativa) ‘Salanova® Hydroponic Red Butter’, arugula (Eruca sativa) ‘Astro’, spinach (Spinacia oleracea) ‘Space’, mustard greens (Brassica carinata) ‘Amara’.
- Lighting during growth: 16-hour photoperiod; daily light integral 8.6 ± 1.2 mol·m−2·d−1 for lettuce and arugula and 9.4 ± 3.0 mol·m−2·d−1 for spinach and mustard greens.
- Treatments: extra light 7, 3 or 1 day before harvest: 0, ∼100, 200, 400 or 600 µmol·m−2·s−1 PPFD of broad-spectrum white light (17:40:43 red:green:blue), or ∼200 µmol·m−2·s−1 of red-blue light (53:1:46 red:green:blue).
- Measured: growth, morphology, photosystem II efficiency and postharvest longevity.
- Publication: HortScience 61(11): 2526-2538, November 2026, https://doi.org/10.21273/HORTSCI19696-26.
- Not reported in the published abstract: the location of the greenhouse, dates and crop duration, the hydroponic system, the light source used for the extra light, temperature, humidity and CO2, the nutrient solution and its EC and pH, the number of plants and replicates, the size of the weight gains and their statistics, and funding.
Links
- The study: End-of-Production Lighting Effects on the Growth, Morphology, and Postharvest Longevity of Greenhouse-Grown Leafy Greens
- The institution: Plant Sciences Department, University of Tennessee
References
- Friedrich, J. R., Armstrong, S. P., Owen, W. G., & Walters, K. J. (2026). End-of-production lighting effects on the growth, morphology, and postharvest longevity of greenhouse-grown leafy greens. HortScience, 61(11), 2526-2538. https://doi.org/10.21273/HORTSCI19696-26