That is a plastic wall behind them. They're on my porch. It started as an experiment to test the design I cobbled together when I built my SiP planters. I didn't expect to get tomatoes off the plants, but I wanted to see how well they did in the SiPs before they succumbed to winter.
We were getting a cold snap one night so I went down to the dollar store and picked up a couple of clear heavy-duty shower curtain liners to make a little tent to protect them from the frost and I stuck a chicken-brooder lamp in the tent. I knew winter was coming, but it was going to warm up after the brief cold snap, so if I could get them through the night, my experiment could continue a little longer. It did continue.
In December and January, the plants kinda stagnated; they were still alive, but the little green tomato clusters didn't get bigger. The plants were supposed to be dead by now, but here it is the middle of February and over the last week or so the tomatoes are getting bigger and ripening and I have new blossoms on the plants.
Upside -- I have tomatoes in February with very little effort on my part. I have new ideas for what to do in the tunnel greenhouse next winter, and my SiP experiment was, so far, a raging success.
Downside -- I want my porch back.