In the autumn of 2021, the business unit Greenhouse Horticulture of Wageningen University & Research investigated the effects of light spectrum on growth and development of four chrysanthemum varieties. Results showed that stem length can be stimulated very well by “end-of-day” lighting with 20 μmol/m²/s far-red light for 30 minutes. Furthmore, days to flowering was reduced, as well as (unwanted) shoot growth in the lowest part of the canopy. The question remains whether comparable effects can be achieved with a lower intensity or a shorter period of far-red light. That would be a good steering mechanism to be control stem length to the desired values. Another question is whether the far-red light at the end of the day is necessary during the entire cultivation period, or whether application during the first period of cultivation is sufficient.

To answer these questions, we started a cultivation of four chrysanthemum varieties under 200 μmol/m²/s full LED in May 2022. Winter conditions were simulated in IDC LED, with greenhouse cooling and maintaining a share of sunlight of approximately 20% and of LED light of 80%. Intensities of far red light at the end of the day varied between 20, 10 and 5 mol/m²/s, and the duration ranged between 10, 20 and 30 minutes. In addition, the percentages of green and far-red light in the spectrum during the day, and plants were also grown at a lower light intensity (100 mol/m²/s).

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Photo Courtesy of Wageningen University & Research