Lighting lessons differ for tomatoes and strawberries in a cold climate

A Canadian cold-climate tomato grower has opted for a combination of LED and less efficient high-pressure sodium (HPS) lighting in the greenhouse in order to ensure enough heat — emitted by the HPS — although the farm's strawberry patch will be LED only.

Sunterra Farms, based in Acme, Alberta, is a longtime pig farm now foraying into fruit and vegetables. It hopes to have its new greenhouses ready to go by November or December. Construction began earlier this year.

Winter temperatures can regularly plunge to -30°C (-22°F) at the location, so family-owned Sunterra was concerned that its 6 hectares of tomatoes might not be warm enough. For that reason, it opted for a mix of LED and HPS toplights. The LEDs come from Eindhoven, Holland-based Signify, and the HPS lights come from another Dutch company, Agrolux, based in Rozenburg.

While HPS lights do not last as long as LEDs and require more power per lumen, their lower energy efficiency means they emit more heat, which can be a positive or a negative, depending on the crop and the climate.

Sunterra decided the extra heat was desirable. The farm is presumably pumping in heat from a dedicated heat source as well.

LEDs can play the role of heat moderator, too. For example, two Benelux tomato farms, Bryte in Holland and Den Berk Délice in Belgium, mixed in LEDs with HPS to keep the climate from getting too hot, as did Dutch flower grower Lugt Lisianthus. Belgium’s Tomato Masters worried there would not be enough heat in a greenhouse lit entirely by LEDs. Tomato Masters took extra measures to assure there would be optimal conditions.

Sunterra did not have the same concern with its 1-hectare strawberry installation.

“Strawberries require a much cooler growing environment, therefore full LED was more suitable to that crop,” a Signify spokesperson told LEDs Magazine.

Strawberries present their own lighting challenges in that they can bud and flower faster than the grower might want. In order to stall flowering, Sunterra is installing LED lamps from Signify that delay the process. The lights in this case are counterintuitively called “flowering lamps.”

“Flowering lamps are used for certain crops only, to prevent the plants from flowering actually,” the Signify spokesperson said. “It helps the strawberry plants to prevent budding.”

Sunterra is also using Signify toplights for the strawberries.

The farm chose not install a control system, the spokesperson told LEDs.

Horticultural solid-state lighting (SSL) and other AgTech systems used in controlled environment agriculture (CEA) will be on the docket at LEDs' annual HortiCann Light + Tech Conference, held virtually this year from Sept. 28–29. Bookmark the HortiCann website to keep up with program updates and register to attend for free.

MARK HALPER is a contributing editor for LEDs Magazine, and an energy, technology, and business journalist ([email protected]).

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