We have had a pretty odd winter here in Utah. I know it's only my second one, so I don't have much basis for that statement, but it has basically been a crazy beautiful spring since early January. That being said, it did get bitter cold for about a week over Christmas and I am happy to report that our little covered wagon out back provided enough protection for the plants to survive!
In reading about planting for a winter hoop-house garden, the goal is for the plants to be pretty well established (ready to harvest) by the time temperatures start to get really cold. The idea is, the hoop house or cold frame essentially protects them from the freezing temperatures allowing you to be able to harvest as needed throughout the winter. In other words, don't count on a lot of plant growth over the winter, more plant protection and preservation. This can get complicated when you're dealing with a small space and trying to let your summer plants go as long as possible before tearing them out… (guilty). Hence, I got a late start to planting seeds in the fall, so the plants were pretty small by the time December rolled around. But, thanks to these unseasonably warm temperatures over the last month, they have grown ever so slightly and we have been able to harvest arugula for a couple salads, a handful of carrots, and cilantro. Since most of the plants weren't big enough to harvest over the winter, I am hoping they will survive any future temperature dips and will take off as it warms up this spring - a bit of a head start if you will. Right now there are little kale, spinach, green onion, lettuce, arugula, cilantro, and carrot plants hanging in there through the winter, which are all cool-season plants for spring, so I'm keeping my fingers crossed!
It's hard to tell from the pictures above, but the kale, spinach, onions, and carrots have grown a little bit, and the kale just looks stronger than it did in December. I tore out some of the lettuce plants that had some freeze damage after Christmas, hence the empty space in the middle. The arugula and cilantro have continued to grow as we harvest.