In the Garden:
Northern & Central Midwest
My low tunnel hoop house is still providing me with greens, even in the dead of winter.
Extend Your Vegetable Season
This has been the perfect year to extend the season with use of a cold frame or hoop house. It's been unusually warm in my area, all the way into December, and the hoop frames I put over my raised beds have given me wonderful greens all the way through to the first of the year.
Using different methods can enable you to add four to six weeks to the front and back ends of the growing season. Simple plastic cloches and plastic-covered cold frames raise night temperatures 4 to 5 degrees. Putting an insulating blanket over a cold frame will raise the temperature 8 to 10 degrees, and putting black painted bottles filled with water inside the covering will raise the temperature 12 to 15 degrees as they release stored daytime warmth at night.
These boxes with glass or plastic lids allow you to do early spring and late fall planting by protecting plants from strong spring winds, shedding snow, and best of all, absorbing and storing solar warmth. For construction, you can simply stack a perimeter of bricks or bales of straw and cover it with a window sash. Or you can actually build a wooden box and cover it with an old storm window.
A cloche is simply a cold protector for a single plant. You can use all manner of found or recycled materials, or you can purchase ready-made cloches. You can use plastic milk jugs or clear plastic bottles or purchase bamboo cloches that are covered with plastic or fabric. You can also purchase fairly expensive designer cloches (they can run up to $25.00 apiece, but they are certainly beautiful!). Just remember that the thicker the material, the better insulation it will provide. Also, heavier cloches will stay in place without staking.
Tunnels run the gamut of materials and construction, and you can build your own fairly simply or purchase kits, which make it easier but more expensive to tent the garden. The best constructed tunnel is low to withstand wind and very sturdy to withstand snow load in our climate. You can use fence wire, concrete reinforcing wire, purchased metal hoops, one-inch PVC pipe, or even saplings to make the supports.
The supports are then covered with plastic to extend the season. When fitting plastic to the supports, make sure to cut enough for at least a two-foot overhang on both sides, and use edge weights such as bricks, landscape timbers or stones to hold it in place. Again, a little ingenuity will let you figure out a system that works for you. Once your tunnel is built, you can cover it with old blankets or bedspreads on frigid nights to increase the insulation.
Ways to Increase Temperature
Locate your frame or tunnel near the wall of a heated building, insulate the walls, sink the foundation into the soil, use double glazing for the top, or add a heating cable.
The best plants to use are those that are considered cool season crops, such as lettuce, spinach, and other greens. The critical part of the equation is to select plants that don't need much heat at night. Keep in mind that plant growth in late fall and winter is limited not only by low temperatures, but also by reduced light as the days also get shorter. This makes it harder to mature root crops like carrots, beets, and radishes, but they are certainly worth a try.
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