I'm not sure why Oklahomans think we have to import green produce from foreign countries during our winter months. Comes now some folks from north China and Manitoba in Canada, both of which have winters that are considerably more frigid than Oklahoma City, with plans for greenhouses capable of growing cool season vegetables all winter long, using only the sun for heat, no back-up propane or natural gas or even wood.
Check out "Solar Greenhouses Chinese Style" . See also Evaluation of Solar Greenhouses, a report on a Manitoba Agriculture, Food and Rural Initiatives project, which found that the design used by the Chinese kept temperatures above 0 degrees Centigrade (32 degrees F) when the temperature outside was MINUS 30 degrees centigrade (-22 degrees Fahrenheit).
The design features an insulated north wall and a north facing roof, with a low south wall connected with the north facing angled roof by metal ribs. This is then covered with the typical transparent sheet plastic. An insulating blanket is rolled over the plastic at night. Cheap to build and operate.
Maybe add some fish in tanks and use the water to grow the cool season crops; laying hens and rabbits are another way to add production.
A second great new resources comes from Cornell University -- peer reviewed Organic Production Guides for popular fruits and vegetables, including apples, blueberries, grapes, lettuce, potatoes, spinach, strawberries, and cole crops, including cabbage, cauliflower, broccoli, and Brussels sprouts. Also beans, carrots, peas, and dairy.
A hat tip to HortIdeas Online, one of my sources for accurate and practical horticultural information, for this news bytes today. HortIdeas is a PDF publication, and they have a great deal for group subscriptions, each sent individually to the subscriber's email address (5 minimum for a group). This would be a good source of info for our producers.