Cultivating strawberries in vertical farms is increasing all around the world. Vertical farming can increase food security and the possibility to produce more local food and receive fresh berries all year around. Light is one of the most important environmental factors in plant growth, and especially when we move to a closed environment with vertical farming. Every plant species needs their optimal light intensity and spectra for flowering and berry production, and when light parameters are fully optimized, it is possible to achieve enhanced, maximum yields.
Intensity
Optimal light intensity is crucial for plant growth and performance, for strawberries the optimal intensity should be above 300 µmol m−2 s −1 as low intensities can result in decrease in yield. Daughter plant production and their dry and fresh weight is also increased by increasing intensity. Higher intensities can also result in higher sugar content in the berries. With increasing intensity, it is good to always consider the electricity costs and that the accumulated yield will cover the costs.
Spectrum
Spectrum also plays a pivotal role in the growth development and yield of strawberry plants. Understanding and utilizing optimal spectra, growers can enhance their overall yield, plant health and fruit quality. Different wavelengths of light affect different areas such as photosynthesis, nutritional values and pigmentation for example.
Red light drives photosynthesis and photomorphogenesis, biomass accumulation and cell differentiation. Added far red can induce earlier flowering and affect plants morphology, to boost biomass. Blue light contributes to more compact growth and boosts secondary metabolite production and regulates stomatal functions. UV- light is also known to boost secondary metabolites, increases flavonoid production and helps with disease control. Green light penetrates to the lower parts of the canopy and affects morphology like leaf size and can be very beneficial to many plants.
There are lot of horticultural lights out there that consist of mainly red and blue, because plants utilize these wavelengths very efficiently and can grow and produce a decent yield. But without a wider range of spectrum, the nutritional values, sugar content and even the yield size can be compromised. It is also important to note that working under with just red and blue light can be difficult, as it is very hard to observe leaf, flower and berry colour, and it is easy to dismiss leaf damage or moulds and pests.
Valoya investigates the best spectrum for growing strawberries
Valoya has conducted trials with strawberries in a growth chamber, to define the best possible spectrum for strawberry vertical farming purposes. Measurements were taken of phenology, yield, chlorophyll and flavonoid content, morphology, measure of the dissolved solids in a liquid (sugar content).
What experimental conditions did we use?
Trials were conducted in a growth chamber in Helsinki in 2024. The variety that was used was `sonsation`, which is suitable for vertical farming. Photoperiod was 10 h, intensity set in the beginning to 250 µmol/m2/s on pot level. Due to research practicality, each plant was potted in an individual pot.
Spectra that were tested included Valoya’s AP67 which is broad spectrum dominant in red and blue, but also containing far-red light, as it was designed for strong generative growth and to induce flowering in some species. The competitor spectra selected was composed of red and blue LEDs, designed to boost biomass
Valoya’s used LL-series fixtures, designed for vertical farming, tissue culture and for growth chambers.
AP67 produces sweet strawberries, better visibility, and easy-to-pick fruits
Spectra had no effect on the phenology of flowering time of strawberry `sonsation`. Treatment with AP67 resulted into higher flavonoid content in leaves over R: B treatment.
Figure 1. Cumulative sum chart of the number of fruits between Valoya’s AP67 spectrum and competitors red and blue (R: B) spectrum throughout the second experiment.
AP67 did have higher sugar content (BRIX %) over R: B, although we did not detect statistical significance. This result however supports the blind taste test conducted, where AP67 was ranked the best tasting amongst participants.
Even though spectra had no statistically significant effect on fruit size (fresh weight or length) on either of the experiments, the morphology of the entire plant was bigger with AP67 treated plants over competitors R: B treated plants. There is a major benefit in having longer fruit stalks, because this makes harvesting more efficient and easier.
Figure 2. Side by side comparison of strawberry plant grown under competitor R: B spectrum (left) and Valoya’s AP67 spectrum (right). AP67 treated plants were consistently larger than R: B treated plants (p=<0,000).
The difference in light quality was also notable in terms of visibility and working conditions. Working under just red and blue spectrum made it very difficult to observe plant health and development, it is also straining for the eyes. With AP67 spectrum it is possible to get the benefits of red and blue peak alongside with the broader spectrum with other added wavelengths like green and far red, that help penetrate the light through the canopy to the lower leaves and benefitting the morphology of the plant and making the work environment more pleasant and efficient.
Figure 3. Strawberry plants observed under R: B spectrum on the left and wider but R: B dominant AP67 on the right. The difference in observing the plant quality and health can be clearly seen with this side-by-side comparison.
References:
Avendaño-Abarca, V. H., Alvarado-Camarillo, D., Valdez-Aguilar, L. A., Sánchez-Ortíz, E. A., González-Fuentes, J. A., & Cartmill, A. D. 2022. Response of strawberry to the substitution of blue light by green light in an indoor vertical farming system. Agronomy, 13(1), 99.
Swann, K., Hadley, P., Else, M. A., Pearson, S., Badiee, A., & Twitchen, C. 2021. The effect of light intensity and duration on yield and quality of everbearer and June-bearer strawberry cultivars in a LED lit multi-tiered vertical growing system. In IX International Strawberry Symposium 1309:59-366.
Xu, X., & Hernandez, R. 2020. The effect of light intensity on vegetative propagation efficacy, growth, and morphology of “Albion” strawberry plants in a precision indoor propagation system. Applied Sciences, 10(3), 1044.
