Abstract/Summary

Traditional UK strawberry production is limited to the summer months. However, consumer demand for strawberries continues out-of-season driving importation. UK season extension is possible with glasshouse technology and supplementary lighting. High Pressure Sodium (HPS) lamps have been the principal lighting source in glasshouse strawberry production. However, HPS lamps have poor energy efficiency, limiting their application in growing systems. LED lamps are a more energy efficient alternative which produce less radiant heat, can be positioned closer to plants and offer a tuneable spectrum. The benefits of LED lighting in strawberry production have yet to be fully realised. This study aimed to examine the use of LED supplementary lighting in out-of-season strawberry production. Three series of experiments explored the LED light spectrum and intensity, its application within a vertical growing system and the potential for industry scale implementation. These LED lighting treatments were combined with other factors such as, temperature, CO2 enrichment, night-break lighting, cultivar and plant growth regulators, and were compared alongside unlit and HPS controls. Data were recorded on fruit yield, photosynthetic rate, fruit quality, time to flowering, fruit ripening time, plant growth, and light and temperature environments under the different lighting treatments. This work confirmed the effectiveness of LED lighting in the production of out-of-season strawberries. LED light intensity showed a strong positive correlation with yield and photosynthetic rate up to an optimum at roughly 300 µmol m-2 s -1 . The blue:red light ratio did not have a significant effect on fruit yield. Far-red light improved fruit earliness and plant canopy and truss expansion. Green light did not detrimentally effect yield and improved visibility for workers. An optimum light spectral ratio for glasshouse strawberry production considering earliness, energy and cost efficiency, optimum yield and worker environment, would be 5:10:5:80 blue:green:far-red:red. Furthermore, high yields per unit area were successfully produced in a vertical growing system. However, this was not yet cost effective, but the lighting strategy can be adjusted to improve efficiency. This work was successfully expanded to a commercial scale and provides guidelines for growers and lighting companies to optimise the implementation of LED lighting in out-of-season strawberry production.