The greens are still growing in my cold frame. I think the lowest temperature they have seen in the frame is about 28*F. This was on a very cold night that went into the teens outside the frame. The remote thermometer monitors below show the cold frame temperature on the big display and the outside temperature on the smaller one.
I was worried to see the plants all wilted down, but they perked up as the temperatures came up. I had to bring a bucket of water out to water the plants yesterday as the soil is drying out.
Since its my first year with a cold frame, I not sure how long I can wait to harvest. So far, so good. But it seems some very cold weather is heading east on Wednesday and I will plan to harvest most of the greens before this.
I never did get a heater or even extra insulation added to the cold frame. Still impressive how well it has done to extend the harvest time.