A few of my Endives succumbed to the heavy frost last weekend. They went black and mushy, so they had to be consigned to the compost bin. Fortunately most of them survived, as did the Lettuces. However, I decided that they deserved a bit of protection, so I have covered several of them with clear plastic cloches:
This one is a nice Oak Leaf lettuce, nearly big enough for using.
This is an Endive, seen through the forest of sticks that I use to try to deter foxes, badgers etc from digging in the raised bed (it's only partially successful).
This is one of the unlucky ones. It will be harvested next time I need some salad.
These cloches will only provide limited protection. The temperature inside won't be much different from the outside temperature. Their main advantage is that they shield the plants underneath from wind, and they prevent frost forming directly on the leaves.
Most people think of lettuces as being frail, and very susceptible to frost damage, but actually if you choose wisely there are several varieties that will do OK in the Winter-time, especially if grown under cloches. A couple of years ago I tried "Winter Density" and "All Year Round" and they both did reasonably well under cover. You can read a post about this HERE.
Dave from Our Happy Acres (our host for Harvest Monday) also wrote a post a couple of years ago on this subject, which you might like to read. Follow this Link.