Underneath a mound of earth in a small northeast Minneapolis backyard something groundbreaking is happening: Food is growing in the dead of winter.

“It’s so hot in here that the tomatoes are out of control,” said Greg Strong, one of several volunteers who tend the experimental garden. They call it a walipini — a Bolivian word for a solar-heated greenhouse with earthen walls.

It sits in the backyard of Sarah Lawton, pastor of the nearby Northeast United Methodist Church, where volunteers also tend a large community garden on the church’s front yard. Volunteers built the makeshift greenhouse at the parsonage, hoping to create a prototype for how to grow food year-round in harsh climates.

But this fall, the experimental garden was challenged by the city in response to complaints that it was “an eyesore,” ­Lawton said. Now the city is studying the issue and developing guidelines for regulating garden structures like the one in her backyard.

“There isn’t anything about walipinis in the city code,” noted Bruce Robbins, a church trustee.

The walipini saga began in summer 2015 when church volunteers tore out the lawn and dug an 11-by-7 hole about 6 feet deep in Lawton’s backyard. They built the structure using old windows and other salvaged materials. First they sought a permit from the city, but were told they didn’t need one.

Now in its second winter, the walipini has produced hits and misses. The volunteers have harvested bushels of Swiss chard, lettuces and strawberries. But “carrots were a disaster,” Strong said. “We got long greens and stubs of carrot.”

Over the months, the walipini has attracted hundreds of curious visitors — and at least one detractor. (The city declined to disclose how many complaints it received or the identity of the complainants.)

In October, the city gave Lawton 10 days to remove the walipini. But she and her fellow volunteers weren’t ready to pull the plug on their experiment.

“I have seen how many people are inspired by this,” Lawton said. “That’s why I’m fighting for it. This is the first, but not the last. Others will be built.”

She put out a call on Facebook to help save the walipini.

“Hundreds of people responded,” she said, and the volunteers won a “stay of execution” until Dec. 1, giving them time to work on the walipini, which they admit had “slumped a bit” following heavy fall rains that eroded the earthen berm.

The volunteers organized two workdays to build up the berm and add a retaining wall at the base, then sent photos of the improved walipini to the city. Now they’re waiting.

“It’s up to them to decide whether it fits an existing or a new category,” said Tim Jordan, an architect who lives in the neighborhood and helps tend the walipini. “It could fall under the category of greenhouse or hoophouse” or other structures that extend the growing season, he added. “This is how change happens — small projects that push the envelope.”

First Ward Council Member Kevin Reich asked city staff to study the issue and make recommendations for defining and regulating sunken greenhouses.

“It’s a new concept for do-it-yourself agriculture,” Reich said.

When he first heard about it, he had no idea what was being talked about, he admitted. “I said, ‘A what-a-pini?’ But I should stop being surprised when I hear about the next new thing. Northeast is known for trying new things, and the DIY ethos is strong in Northeast.”

Reich views the walipini debate as part of the continuing conversation about urban agriculture.

“Urban agriculture used to be considered an oxymoron,” he said. “But we’re moving away from that very swiftly.”

The city legalized urban agriculture in 2012.

“From 1963 to 2012, all urban farming was banned,” said Russ Henry, co-chair of Homegrown Minneapolis Food Council, which advises the city. “Now folks have their chickens, beehives and little farmers markets. This is another in a series of growing pains. We’re working on a definition for [walipinis]. Hopefully, we can show the City Council this is a needed and necessary tool for folks to experiment with cold-climate growing.”

The city does have existing language defining cold-frame gardening, said Henry, who argues that a walipini “is like a cold frame that got a little bigger.”

Also awaiting direction from the city is Sisters’ Camelot, a nonprofit that provides organic produce to low-income neighborhoods.

The organization, which has a garden in south Minneapolis, dug the hole for a walipini last spring, inspired by the one in northeast, and were informed that a walipini wasn’t permitted under current city code, but that the city was working on the issue.

“So we stopped,” said volunteer Andy Latham. “I think they’ll let us build it eventually. It is just a greenhouse — with a 4-foot basin.”

Reich anticipates that the city will complete its study of the issue in time for the spring growing season.

Whether or not walipinis are deemed unsightly is only part of the issue. “It’s hard to legislate aesthetics,” Reich said. Public safety concerns also need to be addressed to ensure that any walipinis are soundly engineered and won’t collapse. “Does it really belong in Minnesota? Time will tell.”