Greenhouse Strawberry Production Recommendations
Consumers are demanding more local year-round greenhouse-grown berries, and growers have been quick to answer with increasing strawberry production in controlled environments. Strawberries can be complex to grow but some species are well suited to indoor growing environments. Since greenhouse strawberries are grown in the off-season and low-light months (September-April), supplemental lighting can help achieve consistent light levels for maximum production. Greenhouses can also offer a better-growing environment by controlling light, temperature, CO2, and other environmental parameters.
In this article, we cover the basics behind greenhouse strawberry production and how supplemental lighting can help achieve optimal DLI (daily light integral) levels and improve flower induction. Our research comes from firsthand experience, having worked with some of the largest greenhouse strawberry producers in North America, and leading-edge research in controlled environment strawberry production.
Strawberry Cultivars
There are two kinds of strawberry cultivars, June-bearing and ever-bearing.
June–bearing cultivars have a critical photoperiod and are short-day flowering plants. Flowering is initiated under daylengths of 8-13 hours and cool temperatures. If day length or temperatures exceed the maximum, flower initiation stops.
Ever–bearing cultivars are known as facultative long-day plants. They develop more flowers under long days but develop flowers regardless of day length. Flowering can be initiated with supplemental lighting or night interruption lighting. Flowering is also affected by temperature and will be suppressed if temperatures exceed 30 degrees Celsius. For most growers, ever-bearing varieties make the most sense for greenhouse production.
Light Recommendations
Strawberries can produce fruit under low light levels. However, this is not optimal for high yield, high productivity greenhouses. DLI, which measures the amount of light received over 24 hours (measured in moles per meter squared per day), is a good way to guarantee your plants receive the recommended amount of light for achieving high productivity and yields.
It is recommended that growers target a minimum DLI of 12 mol/day. However, a DLI between 20-25 mol/day is best for optimal productivity. Going above this limit can stress strawberry plants and reduce productivity. Some research suggests strawberries show a steep diurnal decline of net photosynthesis and that the morning hours are critical for promoting photosynthesis.
Temperature Recommendations
Managing temperature is important for controlling the flowering of strawberry plants. Literature recommends keeping daytime temperatures between 68°F-75°F (20-24°C), as exceeding this range may limit flower initiation and stress plants. Strawberry plants require lower nighttime temperatures to produce high-quality fruit. In general, fruit size increases at lower temperatures, and sugars and flavor improve when plants are grown at low night temperatures between 50°F-54°F (10-12°C).
Humidity Management
Strawberry plants tend to be sensitive to humidity. In dry environments, low humidity may become an issue and cause the physiological disorder of tip burn/calyx. Tip burn is a calcium deficiency in the leaves caused when plants excessively transpire, meaning the calcium goes mostly to the leaves instead of developing tips/shoots.
Research suggests at least 3 hours of high humidity at night, around 90-95%, is needed to avoid tip burn. This helps slow transpiration rates and allows calcium to reach the growing tips. After this period, humidity should be lowered to dry plants out and help prevent foliar diseases. Daytime humidity levels should be between 40-60%.
CO2
CO2 enrichment is useful for enhancing photosynthesis when light levels are low and vents are closed in the winter months. Since CO2 can drastically fall during these times, supplementing with CO2 (with concentrations around 1000-1500ppm) can help increase yields and overall plant productivity.
What kind of lighting should I use?
Both HPS and LED luminaires could be great options for strawberry production depending on your application and crop needs. We have seen great success with using HPS horticultural lights for strawberry production. Their tried and true spectrum is perfect for flower initiation, and the radiant heat can help keep heating costs down during winter at northern latitudes. An HPS could be especially useful when planning to switch out your crops for half the year and grow crops such as tomatoes or cucumbers that are proven to also grow well under HPS. LEDs, because of their low heat load and more targeted spectrums, may also be good for growing strawberries. However, trials should be done before any large installment, as responses will vary by strawberry cultivar. For more information on developing a light plan for strawberry production, check out our Request a Light Plan page.