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New Mexico State University

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Cold Frames Keep Vegetables Growing, Cash Flowing

DIXON - Despite freezing weather, Dixon grower Matt Romero continues to grow and sell fresh greens at the Santa Fe Farmers Market using cold frames that allow him to produce salads, arugula and other crops through the winter.



Dixon-based grower Matt Romero examines drip lines and greens in one of the three cold frames he uses to grow vegetables during the winter. Solar-heated hoop houses like this one are low-cost, low-tech alternatives for small-scale growers who can't afford to build expensive green houses that can cost upwards of $12,000. (NMSU Agricultural Communications photo by J. Victor Espinoza)

"Cold frames have changed everything," Romero said. "Most growers in the north gleaned the last of their produce when the first frosts hit in October, but in November I was just beginning to harvest my winter produce."

The lack of competition has meant premium prices for Romero. Since November, he's been selling lettuce and spinach at $8 per pound, about 35 percent more than during the normal growing season.

"It's usually a very competitive market, but not on the off months," Romero said. "I'm getting better prices, and the produce sells fast because there aren't enough winter growers to satisfy demand. The cold frames are really helping farmers like me keep the cash flow going."

About 50 commercial producers and dozens of backyard growers are now using low-cost cold frames, or solar-heated hoop houses, to continue growing in winter, said Del Jimenez, an agricultural specialist with New Mexico State University's Rural Agricultural Improvement and Public Affairs Project (RAIPAP), based in Alcalde. Largely because of cold-frame production, farmers markets in Santa Fe and Los Alamos remain open during winter, he said.

"Conventional growers are typically limited to a five-month season from May to September, but cold frames can extend the season to about nine months for many crops, and they allow year-round production for cold-hardy vegetables," Jimenez said.

Low construction costs make cold frames a viable alternative for small-scale growers like Romero, who often can't afford to build fully equipped greenhouses. Generally, greenhouses include heaters, coolers and irrigation and fertilization systems. They can cost up to $12,000 or more depending on size, quality and features a grower installs, Jimenez said.

In contrast, simple cold frames cost $200 to $500 to build. A cold frame is much smaller and lacks temperature controls and other operating systems. Construction is limited to a basic frame with plastic covering, Jimenez said.

"With just one or two helpers, a grower can build a cold frame in about three hours and for as low as 200 dollars," Jimenez said. "Given the simplicity and benefits, more and more growers are setting them up."

Romero put up three cold frames on his 2-acre plot in Dixon, for about $300 each. The hoop houses, which include drip irrigation systems, are 14 feet by 85 feet, giving Romero about 3,500 square feet of growing space.

"These are low-tech, low-cost designs that are easy to build," Romero said. "They basically pay for themselves."

Hoop houses protect crops from wind and cold while trapping solar heat inside.

"The plastic frame creates an extremely warm microclimate," Romero said. "Even in the dead of winter, it heats up to 90 degrees or more. It gets so hot inside I have to open the doors to cool it down during the day."

An added benefit for plants is the humidity generated when cold air heats up inside, making the soil moist and spongy. Cold winter nights help conserve plant sugar, improving vegetable quality and allowing plants to stay fresh longer than in the normal growing season. That means producers can stretch the harvest through most of the winter.

"The vegetables hold better in the cold, so I don't have to rush to harvest and sell," Romero said.

Still, production is confined to vegetables that grow well under the limited sunlight of short winter days, such as lettuce, chard, arugula, spinach and kale.

NMSU is now experimenting with a variety of cold frame structures to suit the needs of growers, such as taller hoop houses that can accommodate tractors and other equipment, Jimenez said.

Ron Walser, a fruit specialist with NMSU's Sustainable Agriculture Science Center at Alcalde, is studying cold frames to extend the growing season for strawberries and raspberries.

"The berry harvest stops when the fall frost begins in mid-October, but with hoop houses growers can extend the harvest through November," Walser said. "Cold frames can also protect berries from early spring frost."

Don Bustos, who grosses about $90,000 annually from his 4.5-acre organic farm in Espaņola, was one of the first northern growers to start using cold frames based on NMSU recommendations. He bought three prefabricated hoop houses six years ago for about $1,200 per structure. Now, winter sales account for about 25 percent of earnings.

"I have a steady income throughout the year now," Bustos said. "That alleviates the pressure to produce intensively in summer to put aside cash for the off season. My winter earnings are adequate to cover basic business and household bills. I don't make as much as in the summer, but it helps a lot."