Kale doesn't mind frost. In fact, the leaves taste sweeter after a frost has hit them.
There are many plants that don’t mind frost and other plants that continue to thrive for several months longer if they receive some type of frost protection. Kale, for example, doesn’t mind frost – and will thrive outdoors throughout most of the winter, even in United States Department of Agricultural hardiness zone 5. Brussels sprouts is another great plant that survives throughout the winter outdoors without protection. If you wish to go an extra step and provide some type of frost protection, such as a row cover or cold frame, there are a number of plants that will survive the winter.
Grow a variety of salad mixes in a cold frame and eat fresh salads all winter long.
Lettuce is one of the easiest plants to keep alive throughout the winter – and the one I recommend beginners – or naysayers – try their hand at. Plant lettuce seeds in mid-August through mid-September. Cover the plants with a cold frame once the frost threatens. Most of the time it is not necessary to water or vent the cold frame during the winter months, however until winter sets in you may need to do this.