B.C. has a reputation for abundant bud, but Ontario Provincial Police say marijuana growers in their province are starting to rival their western counterparts.

"We're well on our way to competing with B.C.," said OPP Det. Sgt. Paul Henry on Wednesday, almost a week after a massive outdoor grow-operation bust in eastern Ontario, that was believed to be the largest ever in Canada.

Henry is the unit commander for the OPP's drug enforcement section in Ottawa and has been with the section for 22 years, but said he was still impressed by the 40,000 plants worth about $40 million hidden in a cornfield outside Pembroke, Ont.

"In all of my years, I've never seen anything like this," said Henry, who noted that the average indoor grow-op has about 1,000 plants.

Police raided the farm last Thursday after receiving a tip, followed by confirmation from RCMP who surveyed the site from a helicopter.

The marijuana was mixed in among stalks of corn more than two metres high in an area as large as seven or eight football fields, that was surrounded by a thick buffer of just corn, Henry said.

As he walked through, "I was bumping into marijuana plants right at my eye level, and I'm over six feet tall."

The plants were irrigated using plastic piping hooked up to a pond and an above-ground swimming pool. The farm was unremarkable, he said, with a tree-lined driveway, a small enclosure containing about 20 sheep and a farmhouse. Inside the building, police found racks of drying screens, fans and heaters, Henry said in an earlier interview.

Growers may have reaped crop last year: OPP

On Wednesday, Henry said this may not be the operation's first year.

"It is possible that last year there was a crop as well but we certainly haven't gotten to the point in our investigation that we're absolutely sure," he said.

Neighbours had mentioned that last year corn had been grown and then plowed under without being harvested.

Henry said corn is often used to hide marijuana grown in Ontario, especially in southwestern Ontario, and that police have seen an increase in grow-ops and their associated problems in recent years. Some have been the result of "pot pirates" who try to steal a grower's crop.

"There's been abductions, shootings, traps set in these fields."

Henry said large, commercial-scale operations like the one found last week typically produce high-quality marijuana destined for the U.S. He added that police are trying to raise awareness about the scale of the problem and its potential consequences, including the strain on police resources.