Extending growing season in the north

Mini domes and LED lights inside greenhouses can extend lettuce season into early winter in the north, a study by College of New Caledonia in Quesnel found.

In a greenhouse at the CNC Quesnel campus, researchers tested a system of mini domes within a greenhouse combined with supplemental light to extend the growing seasons of romaine lettuce, butter crunch lettuce, and scallions.

CNC Biology instructor Jennifer Catherall said these crops tend to have a lucrative sow earlier in the year but can be difficult to grow late season in greenhouses due to lower light intensities at that time of the year.

Two crops were sowed. One, in late August and another in the middle of September. The crops were observed under four growing conditions including LED lights in a dome, LED lights with no dome, a dome with no LED lights, and finally no dome and no LED lights. They were harvested in mid-November and mid-December.

“The addition of LED lights inside the minidome provide the plants with supplemental light and also extra heat,” said CNC researcher Araham Gazana. “These two are essential to keep the plants alive and growing during harsh winter conditions.”

The study found that the addition of only an insulating dome without supplemental light did not appear to provide substantial benefit to plant growth. This, Catherall said, could be the result of CNC’s polymer greenhouse, noting that growers with a traditional greenhouse might see better results from a dome. The use of low-cost supplemental LED lighting at the correct light intensity, however, resulted in an increase in production. 

“Plants grown with lights grew bigger and faster,” Catherall said. “This method could allow for producers to harvest lettuce and scallions just prior to winter farmer’s markets and diversify the produce that’s usually available at this time of year. Future studies could test hardy Asian greens and Mesclun salad greens grown in a similar environment.”

Mackin Creek co-owner and manager Rob Borsato said market gardeners, horticulturalists, and others involved in the growing and selling of local produce are always exploring ways to extend the growing season.

For this project, CNC’s Applied Research and Innovation received funding from the Canadian Agricultural Partnership under the Farm Adaptation Innovator Program delivered by the Climate & Agriculture Initiative BC and partnered with the Scientific Advisory Committee of the Cariboo Agricultural Research Alliance and Mackin Creek Farm.