Hydroponic Strawberry supplemental lighting


Supplemental Lighting Basics

Flowering response of strawberry plants, particularly their temperature-photoperiod interaction, is a complex response and relatively unknown. In contrast, when one pursues off-season strawberry production, understanding the flowering responses of cultivars of interest is critical. Greenhouse allows various techniques of controlling flowering, which is generally well practiced in floriculture and ornamental industry in the United States and in winter strawberry production in Japan.

Strawberry plants naturally respond to day length for flowering as well as dormancy. Ever-bearing strawberry cultivars (varieties) are generally known as facultative long-day plants (Nishiyama and Kanahama, 2000), developing more flowers under longer day. Therefore when everbearing cultivars are used during winter short days, having low intensity photoperiodic lighting to promote flowering may be worth considering. At University of Arizona we apply 4-hour photoperiod extension at 2-3 micro-mol/m2/s light intensity (or ~20 footcandle). June bearing varieties generally exhibit short-day plant response and their first flower cluster development is generally determined by the natural day length in the fall.  However, their actual photoperiodic response is often temperature dependent and unfortunately we have limited information regarding the photoperiodic responses of US cultivars.  Recently, we reported photoperiodic responses of selected US cultivars (Garcia and Kubota, 2017). However, more complete information on especially the temperature-photoperiod interactions is needed to develop flowering control strategies. The following is a summary table published for Japanese cultivars.

Table. Temperature x photoperiod general responses of Japanese strawberry cultivars (Translated from the table published in the Saga Prefecture ‘Strawberry Cultivation Manual’)


In Japan, where winter production of strawberry is based on the use of June-bearing cultivars (varieties) in unheated or minimally heated greenhouses, supplemental lighting is sometimes applied to prevent the plants from entering into dormancy.  Japanese experimental stations recommend applying several hours of day extension lighting (at low irradiance) during the winter months to maintain the vegetative growth of plants.  A good sign of the need of day extension lighting is the plant architecture. When plants exhibit short petiole and height, it is usually an indicator of the need of extending day length.  Behind this technique, there is a good understanding of cultivar specific responses to temperature and photoperiod.  As mentioned earlier, June-bearing strawberry cultivars are generally classified under short day plant, but the flowering response to day length interacts with temperature.  When 24-h average temperature is lower than a threshold temperature (12C in above table), most Japanese June-bearing cultivars develop flowers regardless of photoperiod. Therefore day-extension lighting seems to work to prevent dormancy without inhibiting flowering induction.  Some studies have been done to find temperature and photoperiod interactions of US cultivars (e.g., Bradford et al., 2010), but more information is needed for various cultivars under site specific conditions.

Typical light quality for photoperiodic lighting is traditionally incandescent lamp which emits good amount of far-red light (700-800 nm). Although the light intensity to induce long-day response is as low as 1-3 micro-mol/m2/s PPF, use of more energy-efficient lighting is desired. Traditionally, irradiance was measured using lux and footcandle, units considering the response to the human eye, which should be avoided for assuring expected plant response using different light sources including light emitting diodes (LEDs). A quantum sensor should be used which measures photon flux (micro-mol/m2/s PPF). Research has been done by many greenhouse scientists to find a better lighting option. More information on LED lighting applications in greenhouse can be found in the SCRILED consortium page at Michigan State University (http://leds.hrt.msu.edu/).


Bradford, E., J.F. Hancock, and R.M. Warner. 2010. Interactions of temperature and photoperiod determine expression of repeat flowering in strawberry. J. Amer. Soc. Hort. Sci. 135:102-107.

Garcia, K. and C. Kubota. 2017. Flowering responses of North American strawberry cultivars. Acta Hort. (in press). [View our poster presented at ISHS International Strawberry Symposium (Quebec, Canada) in 2016: Strawberry symposium 2016.pdf]

Nishiyama, M. and K. Kanahama. 2000. Effect of temperature and photoperiod on the development of inflorescences in everbearing strawberry (Fragaria ×ananasa Duch.) plants. Acta Hort. 514:261-267.

Updated (12/28/2016)

Fig. Day extension lighting at University of Arizona for promoting long-day response of ever-bearing strawberry plants.