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Boosting strawberry quality with dynamic LED lights

In recent years, Canada’s strawberry industry has witnessed a significant surge in interest and production, with growers increasingly turning to greenhouse cultivation methods to meet the rising demand for year-round fresh fruit.

According to Statistics Canada’s annual production report, more than 6.2 million pounds of greenhouse strawberries were produced in Canada in 2022 – an additional 655,000 pounds compared to 2020. Statistics Canada also reports that sales of greenhouse strawberries increased 19.1 per cent to $18.5 million in 2021 due to higher prices and increased production.

“There’s a lot of momentum and a lot of interest in figuring out how to do it best and optimize production,” says Rose Séguin, agronomist at Sollum Technologies, of the movement toward greenhouse-grown strawberries.

Determining best practices for greenhouse strawberries

 According to Agriculture and Agri-Food Canada’s Crop Profile for Strawberry in Canada (2019), greenhouse strawberry production systems can vary and can include both soil-less media and soil-based systems. Both June-bearing and day-neutral varieties can be grown in a greenhouse. But, like other greenhouse crops, environmental conditions play an important factor.

“…Lighting, humidity, and temperature need to be closely monitored and controlled for successful production,” the report advises. “Strawberry plants require a high amount of light and therefore supplemental lighting is needed, particularly during the early spring, late fall, and winter months.”

Supplemental lighting isn’t uncommon in greenhouses, with many growers using high-pressure sodium lights (HPS) to improve conditions, especially during low-light seasons. But, Séguin cautions, those who want to grow strawberries with supplemental lights need to take other factors into consideration.

Dynamic LED lights can boost the quality and production of greenhouse-grown strawberries. Photo courtesy of Sollum Technologies.

“One of the challenges [with HPS lights] is that, because there’s a lot of heat being produced, the maximum intensity you can put on a plant is a lot lower as you’ll be contending with the heat,” she says. “Crops like tomatoes and cucumbers tend to respond a little bit better to excess heat, but we know strawberries are a very temperature-sensitive crop.”

Séguin says using LED lights allows a grower to increase the intensity of the light, which can result in higher yield, without the side effect of increased heat. As an example, a grower who might use 120 micromoles with HPS lights, could push intensity to 200 micromoles using LED lights, thereby boosting the plant’s productivity without adding additional heat.

“The more light you have, the more activity occurs in the leaves, resulting in more sugar production and more fruit,” Séguin says.

As with other crops, the impact of light depends on the variety of strawberry grown. “In North America we have a couple of main varieties of strawberries, and we’ve seen major differences in terms of how they respond to being in a greenhouse, and under lights,” Séguin says, adding that as new varieties come into play, adjusting light recipes as the season continues is very helpful. “Typically we would start out a season with a baseline recipe and see how the plants are responding, and based on crop registration data we would make adjustments to the light recipe, whether it’s the intensity, spectrum or photo period, to make sure we’re getting the most out of the plants.”

 Putting lighting to the test

Séguin works with growers like the Savoura Group to help fine-tune growing conditions. Founded in 1995, Savoura spans 40 hectares across 12 production sites in Québec. Their cultivation portfolio includes tomatoes in both conventional and organic methods, and has included day-neutral strawberries since 2017.

Nancy Clermont, a biologist specializing in plant pathology with a decade of experience in agriculture, serves as the research and development and quality assurance director at Savoura. Clermont says Savoura’s staff of more than 400 people grow various cultivars of day-neutral strawberries, ensuring a supply of fresh strawberries for Québec consumers.

“We use artificial light in some of our greenhouses to compensate for the drop in light from October to April,” Clermont says. “This energy increases the productivity and quality of our products during the cold season.”

In 2020, Savoura began trialling dynamic LED lights in a small area, and expanded those trials in 2022, using dynamic LEDs from Sollum Technologies, with a goal of increasing the yield and quality of their greenhouse-grown strawberries. One motivating factor was the ability to moderate the entire spectrum of natural light with a unique artificial lighting recipe.

“The ratio of red to far-red light is a big factor for strawberries,” Séguin notes. “Far-red helps to stretch the plant out, so if we have a strawberry variety that’s very compact, we could increase the far-red to see if we can open the canopy a bit more,” she says. “If a grower needs to trigger flowering, that red to far-red factor becomes really important too.”

This was the case for Magalie Rajotte, owner of Les Serres de la Vallière in Sorel-Tracy, Québec. “With strawberries in the greenhouse, I have a very high demand for light,” she says, noting how especially important lighting is during the winter to prevent plants from going dormant.

During winter of 2022, Rajotte says her strawberry plants had difficulty developing leaves and flower stalks due to the lack of natural light. LED lights from Sollum allowed Rajotte the flexibility to adjust the lighting recipe based on her plant’s needs.

“We modified the recipe to include more far-red light, and my plants changed completely,” she says, adding the flexibility of the system means energy savings as the lighting can be adapted depending on the sun’s luminosity.

Clermont adds this adaptability is also advantageous as it reduces stress to the plant caused by a sudden change of light. “The dynamic LED adapts to the sun’s light intensity by gradually decreasing its intensity. For example, on cloudy days, the LED modulates its intensity rather than closing completely all at once,” she says.

“During the first year of testing, we have had promising results in terms of yield of greenhouse strawberries,” Clermont continues. “We also noticed a tendency to get strawberries with higher sugar levels under LED lighting. The quality of the fruits seems to be improved under this type of lighting.”

Future success

 Another area of research that Séguin points to is the potential for LED lighting to boost fruit quality by mitigating threats like powdery mildew. “There’s a lot of research looking at powdery mildew and other pathogens to see how light affects the resilience of the plant,“ she says. “That’s one of the things we’re really looking into right now, and seeing what kind of treatments we can use to reduce the percentage of fruit affected, or even reduce the severity of mildew on the fruit.”

While mastering light is important, Séguin reminds growers it is hardly the only factor contributing to a healthy crop. All of the other basics need to be present as well: clean material, optimal rootzone conditions, and an understanding of your varieties’ morphological tendencies.

“We can adapt the lighting conditions at any point, but we still need to start with good, healthy plants. And to make the most effective adjustments to lighting throughout the season and maintain a good weekly yield, you need to have eyes on the crop and think at least four to five weeks ahead.”