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With the inexpensive protection of a caterpillar tunnel or Quick Hoops™ low tunnel, many crops can be harvested throughout the winter. Initial crop selection is critical. The best crops for winter harvest include hardy greens such as arugula, mache, mustard, and spinach; and root crops such as beets, carrots, leeks, and radishes. Within those categories, look for varieties with special cold tolerance, denoted with the snowflake symbol.
One of the keys to winter harvest is to plant early enough that the crops have a chance to get close to maturity before the short days of winter arrive. When day length drops below 10 hours, the plants won't be actively growing but, if you have chosen cold-tolerant varieties, they will be able to withstand freezing and thawing so that you can harvest them all winter.
The second key to successful winter growing is to plant sufficient volume to carry you through the cold season. Regrowth is very slow during winter, so assume you'll get only one harvest from a plant during the coldest months. When planning which crops to grow under protective structures, envision how you will harvest during the winter. Root crops, which you need to harvest with a digging fork, are best grown in a high tunnel so you can stand upright while harvesting. An inner low tunnel of row cover on hoops prevents the ground from freezing most of the winter -- a huge benefit when harvesting root crops. Leafy crops also do well under row cover in a high tunnel, but if that space is at a premium, they can be grown under a low tunnel of metal hoops bent with Johnny's Quick Hoops Bender and covered with Agribon AG-30 or AG-70 for maximum frost protection. Whereas in summer you might bury the edges of row cover to keep insects out, in winter you want to be able to gain access to the crops. Use sandbags or rocks to hold the row cover down. For added protection, pound stakes on both sides of the tunnel and lace twine across the top of the tunnel to the other side, going back and forth the entire length. Not only does the twine keep the row cover on the hoops during windy weather, it also allows you to push the row cover up out of the way when harvesting.
For a complete guide to building your own caterpillar high tunnel, please see our manual, which includes many good ideas about how to modify it seasonally.
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Reprinted from JSS Advantage October 2011