Strawberry plant responses to environmental conditions are complex topic. The following is what we consider as the current general understanding based on available literatures.  Responses to specific cultivars need to be examined rather than simply applying this general information. Especially those cultivars that are bred for and cultivated in open fields do not have much information regarding responses to individual environmental factors (and their interactions). Greenhouse controlled environments allow independent control of photoperiod, light intensity and temperature among other factors, and thereby potentially control the plant growth and development to maximize the crop productivity and fruit quality. For environmental conditions for inducing flowering, please refer to the ‘supplemental lighting’ page of this website.

Air temperature.  Optimum temperature of strawberries photosynthesis is reportedly 20C (Kimura, 2008) and many cultivars seem to exhibit comparably high photosynthetic rate between 15 – 27C temperature (Kumura, 2008; Morgan, 2006).  At the University of Arizona we maintains the daytime temperature between 20-24C, depending on the solar radiation. 

Generally, fruit size increases and more sugar accumulates in fruit when the fruit develops at lower temperature.  Therefore, at the University of Arizona we set the night temperature at 10-12C, several degrees lower than other greenhouse crops (e.g., 18C for tomato). A lower night temperature than 10C is acceptable but reduces the overall grow and development rate which is determined by the 24 h average temperature. 

Growers and researchers also need to notice that growing systems would affect optimum temperature setting. Root zone temperature in hydroponic/soilless culture usually has greater diurnal temperature oscillation compared with the soil-based culture system when the same greenhouse/high tunnel system is used.  Root-zone temperature would directly affect the crown temperature where flowers and leaves are developed, while fruit temperature is more directly affected by air temperature when fruits are hanging in the air.  Optimum crown temperature is reportedly at 18C (M. Okimura, personal communication) and localized temperature control by introducing temperature controlled water inside the tubing placed around the crowns showed some success in enhancing production in soilless cultivation.  At the University of Arizona, we have examined the crown temperature control in collaboration with Dr. M. Okimura at Kyushu Agriculture Experiment Station in Japan and achieved ~10% yield increase during our winter production seasons between 2009 and 2011 (Fig. 2).

DLI - Daily light integral.  Light requirement for winter strawberry production is not well known despite the status of widely practiced commercially in Asian countries. However, photosynthetic characteristics measured for strawberries show two interesting aspects in our literature review. First, the photosynthetic saturation point (the light intensity) is reportedly  800-1200 micro-mol/m2/s PPF (photosynthetic photon flux) (Morgan, 2006). The second interesting aspect reported elsewhere is that strawberry plants show relatively steep diurnal decline of net photosynthetic rate (Inaba, 2007), possibly due to the negative feedback of photosynthesis, suggesting that morning hours are critical time for promoting photosynthesis.  Minimum DLI (daily light integral in mol/m2/d) has not been known partly due to the non-linear relationship between plant growth and the cumulative PAR. Day length also affects the dormancy status (rosette-type morphology), largely affecting the light interception (therefore canopy photosynthesis) as well as vegetative growth rate.  More studies are needed to find the optimum light environment (photoperiod and DLI) for strawberry plants. 

Relative humidity.  Strawberry plants are sensitive to dry climate.  Therefore use of fogging is recommended during the day (Morgan, 2006). When they are grown in low relative humidity, particularly low night time humidity, tipburn and calyx burn may be pronounced. At the University of Arizona, we use over-head, high-pressure fogging during the day and below-bench low-pressure misting during the night. See that ‘tipburn’ page for more information.

CO2 concentration.  Since strawberry plants are grown in closed greenhouse/high tunnels in winter.  CO2 enrichment has been practiced for enhancing the photosynthesis under low light conditions when greenhouse vents are closed.

References

Inaba, Y. 2008. Studies on the horticultural characteristics of strawberry for the development of year-round production and the release and the extension of a new cultivar adapted for It. Ph.D. dissertation submitted to Tokyo University of Agriculture and Technology. 93pp. 

Kimura, M. 2008. Vegetative growth and reproductive growth, p.73-96. In: Encyclopedia in Vegetable Crops Horticulture – Strawberry, 2nd Edition. Nobunkyo, Tokyo. 692pp.

Morgan, L. 2006. Hydroponic strawberry production. A technical guide to hydroponic production of strawberries. Suntec NZ, Tokomaru, NZ. 117pp.

(Updated 2/1/15)

Fig. 1 Naturally vented greenhouse for strawberry

Fig. 2 Crown temperature control system examined at the University of Arizona in collaboration with Kyushu Ag Expt Station in Japan.

Fig. 3 Understanding flowering responses is critical for greenhouse strawberry production.