A new crop could be coming to Wine Country.

A measure to legalize marijuana farming in Napa Valley will appear on the ballot in March 2020, after the Napa County Board of Supervisors decided to put the initiative to a vote rather than adopting it as an ordinance.

The proposed measure would greenlight cultivation of marijuana for commercial use in the county’s unincorporated areas — land that is considered best suited to agriculture — but not on the same lot as a winery. It would allow businesses to grow only 1 acre of marijuana apiece — a far smaller area than some vineyards, which can be hundreds of acres.

California voted to legalize marijuana in 2016, but Napa, world-famous for its wine, has not permitted pot farming.

The measure’s boosters are a group of entrepreneurs from the wine and weed industries, known as the Napa Valley Cannabis Association. They argue that the two crops can coexist. The cannabis industry would be a boon for the local economy and could help promote Napa Valley wine to new audiences, they say.

“I was really pleased because for 2½ years all we’ve been asking is for the supervisors to have a discussion about what’s best for Napa Valley in terms of a cannabis ordinance — and that’s what they did at the last minute,” said Eric Sklar, an entrepreneur and co-founder of the trade group.

Sklar said the group is willing to remove the measure from consideration if local officials draft a similar ordinance before early December. But some of Napa’s supervisors have said the issue is of low priority.

The measure faces opposition from members of the local agricultural industry. They worry that cannabis odor could contaminate grapes grown nearby as well as the experience of visiting a winery.

The Board of Supervisors’ decision to place Measure J, the Napa County Cannabis Regulation Initiative, on the ballot was unanimous, according to the North Bay Business Journal.

The vote is set to occur March 3, the same day as the presidential primaries. Backers had gathered thousands of signatures in favor of the initiative — enough to place it on the ballot.

Melia Russell is a San Francisco Chronicle staff writer. Email: business@sfchronicle.com