In the polytunnel at Kingsbury we are experimenting with some of the more unusual tubers from South America including – Yacon, Oca, and Mashua. They cannot be frozen.
Looking at the photo of the snow the thermometer shows the temperature plummeted to -7.oC. Inside the polytunnel the temp can be seen on the probe thermometer sank to -5.7oC but the probe itself was set in to woodchips 4ins deep under a hessian sackcloth. The temp can be seen never went below 1.9oC = nearly 10oC warmer than outside !
This system works and can be set to work for any non-hardy root crops.