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Can LEDs in a polytunnel keep jasmine flowering in winter?
In a winter trial in Tamil Nadu, India, jasmine plants in a diffused-film polytunnel that got four extra hours of 80% red : 20% far-red LED light each evening carried 194.37 flower buds per plant, against 28.90 on plants in the open field.
Jasmine growers in South India have a winter problem: from November to February their plants almost stop flowering, while demand for festivals and weddings stays high, so winter prices climb. A team at Tamil Nadu Agricultural University tested whether a polytunnel covered in diffused plastic film, plus evening LED lighting in different colour mixes, could keep the cultivar CO.1 (Gundumalli) flowering through the cold months (Karthikeyan et al., 2026).
What this means for your grow
If you grow a flowering plant that slows down in winter, this trial is a reminder that both warmth and light colour can matter. Here, the polytunnel alone gave a modest lift, and adding four hours of mostly red light with some far-red each evening gave far more flowers than the polytunnel alone or than the other two LED mixes. The authors call the combination a highly effective strategy for off-season jasmine, but it was one site and one winter, so treat it as a promising lead rather than a proven recipe for other plants or climates.
What did the team do?
The trial ran in a farmer's field in Mettupalayam, Coimbatore District, from November 2024 to February 2025, on one-year-old plants of Jasminum sambac cultivar CO.1. The team compared five treatments:
- T1: open field (the control).
- T2: polytunnel with no extra light.
- T3: polytunnel plus LED light at 60% red : 20% blue : 20% far-red.
- T4: polytunnel plus LED light at 80% red : 20% blue.
- T5: polytunnel plus LED light at 80% red : 20% far-red.
The polytunnels were covered with a diffused polyethylene film that lets through 87% of light and diffuses 62% of it. They were opened for ventilation from 11:00 to 16:00 each day and kept closed overnight to hold in heat. The LEDs ran from 18:00 to 22:00 as an end-of-day light extension, with the light intensity held at the same level for every LED treatment so that colour, not brightness, was the variable being tested. The team counted and weighed flowers and buds every month and averaged the monthly records for each treatment.
What did they find?
- Warmer tunnels: the polytunnels kept mean temperatures 3 to 5 °C above the open field. In December, when the outside minimum was 12.3 °C, the polytunnel minimum was 14.2 °C.
- Flower buds per plant: 194.37 under T5, 78.87 under T3, 70.73 under T4, 44.47 in the polytunnel without light and 28.90 in the open field.
- Flower yield per plant: 52.53 g under T5, 21.32 g under T3, 19.12 g under T4, 14.73 g in the polytunnel without light and 7.81 g in the open field.
- Flower clusters (cymes) per plant: 42.26 under T5 against 5.93 in the open field.
- Bigger buds: 100 buds weighed 28.49 g under T5 against 20.88 g in the open field, and by February buds were longer (2.42 cm against 1.88 cm) and wider (0.95 cm against 0.62 cm).
- Steady through winter: under T5, flower yield rose from 49.21 g per plant in November to 54.76 g in February.
The 80% red : 20% blue mix without far-red did the least well of the three LED treatments on flower numbers and yield, which the authors read as a sign that far-red light is critical for getting the most flowering from this jasmine.
What could it mean?
The authors conclude that a diffused-film polytunnel combined with four hours of 80% red : 20% far-red LED light at the end of the day is a highly effective way to bring on off-season flowering in this jasmine, with the polytunnel keeping temperatures up and the light, they suggest, giving a flowering signal through the plant's phytochrome light sensors (which the study did not measure). They see it as a potentially commercially viable model for year-round jasmine production. Right now the result is most relevant to commercial jasmine growers in similar climates, and it is not a tested recipe for other crops.
What were the limitations?
The authors note that the trial was run at a single location over one winter, so the findings should be read within the conditions of that site, and that testing across more locations and seasons would show how robust the approach is. Physiological measurements, such as photosynthesis, chlorophyll content and phytochrome responses, and a full economic analysis were outside the study's scope.
Trial details
- Where: a farmer's field in Mettupalayam, Coimbatore District, Tamil Nadu, India (11°18′ N, 76°56′ E, 300 m above sea level); dome-shaped polytunnels (3.35 m long, 6.40 m wide, 1.82 m high) and open-field plots.
- Who: Tamil Nadu Agricultural University, Coimbatore (Department of Floriculture and Landscape Architecture, Department of Renewable Energy Engineering and Department of Crop Physiology).
- Crop: jasmine, Jasminum sambac cultivar CO.1 (Gundumalli), one-year-old plants spaced 2.10 × 0.60 m.
- How long: November 2024 to February 2025, with monthly records.
- System: plants in a field, under polytunnels covered with driplock diffused LDPE film (87% light transmission, 62% diffusion, anti-drip, anti-dust, UV-stabilised), or in the open; irrigation, nutrient application and plant protection followed the recommended practices for jasmine.
- Lighting: natural daylight plus end-of-day LED lighting from 18:00 to 22:00 (4 hours); PPFD held at 40 ± 2 μmol m⁻² s⁻¹ at canopy level for all LED treatments. Wavelength ranges: 440 to 740 nm (60% red : 20% blue : 20% far-red), 440 to 670 nm (80% red : 20% blue) and 650 to 740 nm (80% red : 20% far-red).
- Climate: ambient maximum and minimum temperatures ranged from 27.88 to 33.61 °C and 13.18 to 16.73 °C, relative humidity 58.23 to 86.62%, 7.07 to 10.33 hours of bright sunshine a day; polytunnels 3 to 5 °C above ambient.
- Design: randomised block design, 5 treatments, 4 replications, with 4 separate polytunnels for the covered treatments and 4 open-field plots; ANOVA with LSD and Tukey's HSD tests at p ≤ 0.05.
- Results: pooled means for flower buds per plant 28.90 (open field), 44.47 (polytunnel only), 78.87 (T3), 70.73 (T4) and 194.37 (T5); flower yield per plant 7.81, 14.73, 21.32, 19.12 and 52.53 g; weight of 100 buds 20.88 g (open field) and 28.49 g (T5); in February, corolla tube length 1.09 cm (open field) and 1.59 cm (T5).
- Funding and conflicts: financial and logistic support from the Department of Floriculture and Landscape Architecture, Horticultural College and Research Institute, Tamil Nadu Agricultural University. The authors declare no conflict of interest.
- Publication: Plant Science Today, available online 6 November 2026 (Version 1.0), https://doi.org/10.14719/pst.16625. Licence: CC BY 4.0.
- Not reported in the paper: fertiliser rates, EC and pH, the number of plants per plot, and a cost analysis.
Links
References
- Karthikeyan, S., Dinesh Kumar, K., Ganga, M., Thamaraiselvi, S. P., Nithish Kumar, G., Rajkishore, S. K., & Vanitha, K. (2026). Manipulation of light spectral quality for inducing off-season flowering in Jasminum sambac cv. CO.1 (Gundumalli). Plant Science Today. https://doi.org/10.14719/pst.16625