Ontario greenhouses light up

Artificial lighting gives green peppers a purple or red hue. It’s early days for the lighting pepper research at the Agriculture Canada research centre in Harrow, Ont. It is felt specific lighting can improve production and even optimize the level of antioxidants in mature fruit. | Jeffrey Carter photo

HARROW, Ont. — Ontario’s greenhouses are lighting up.

There are 100 acres of tomatoes and cucumbers in the province with supplemental lighting, and researchers are now turning their attention to peppers.

“We’ve done some preliminary work on peppers, and last year the results were promising, and so we’ve expanded our research,” said Shalin Khosla, the greenhouse vegetable specialist with Ontario’s agriculture ministry.

“There are numerous ways of doing this. We think we’re getting close to finding the best combination of lights. There’s still some fine-tuning to do.”

Khosla is working closely with Xiuming Hao, who leads the lighting research at Agriculture Canada’s research and development Centre in Harrow.

Hao and Khosla have found that additional lighting within the crop canopy, which is called inter-lighting, improves plant performance and may even deliver crops with higher levels of antioxidants. The latter is being evaluated by Ron Cao of Agriculture Canada in Guelph, Ont.

Three lighting technologies are being used:

  • high pressure sodium (HPS)
  • plasma
  • light-emitting diodes (LED)

The energy efficiency of all three types have been improving, al-though the newest generation of LEDs remain the industry leader.

The different lighting technologies can be used on their own, but Hao and his associates have found a benefit in using a combination of technologies to deliver the right intensity and type of light.

LEDs, along with being the most energy efficient, can also deliver light in different colours, including red and blue, which best support peak plant growth.

They are typically used for supplemental lighting within the canopy, but can also be used as an overhead source.

Supplemental lighting is viewed primarily as a way to allow greenhouse operators in Ontario’s northerly latitudes to produce crops when natural sunlight is least available — from October to March.

It’s an expensive proposition that will likely require a price premium to be feasible.

However, there are also production advantages in terms of yield, fruit quality and disease management, along with the added benefit of delivering fresh produce to Canadians on the darkest days of the year.

“It comes down to food security,” Khosla said.

“If you want year-round production in Ontario, you need lighting.”

Tomato production can be increased by as much as 30 percent over the course of the growing season with most of the added production coming in winter. Supplement lighting allows tomato plants to be started in September or October and continue producing until July or August, depending on the season.

It’s a similar story with large English type cucumbers. Research shows that overall yield can be close to double with artificial lighting.

A single crop of mini cucumbers planted in September and finished in April under artificial lighting can produce 60 kilograms of fruit per sq. metre and a second 50 kg crop by September. Traditional mini-cucumber production involves three or four crops over the course of a year that may produce 60 kg per sq. metre.

“It’s almost double the yield with lights, and you use less seed and less labour,” Khosla said.

He said artificial lighting is combined with high-wire vine management, which normally is used only for peppers and tomatoes.

The lights are turned on around midnight when electricity rates in Ontario are lowest. If it’s cloudy, they may be left on past sunrise.

“You’re trying to get the day length to 16 to 18 hours, depending on the crop,” Khosla said.

Hao and Khosla said Ontario is among the world leaders in greenhouse lighting research, especially when it comes to fruiting crops on which lighting is manipulated for both the leaves and fruit.

Ontario’s greenhouse acreage has been in expansion mode for decades. There were about 300 acres in 1991 when Khosla joined the agriculture ministry. Today, it’s close to 3,000.

About the author


Stories from our other publications