I built a mini-hoop greenhouse out of PVC pipe and plastic sheeting. I close it up every night and turn on a small heater. It’s been as low as 20 degrees at night, so it’s working. I forgot to factor in how low the sun gets in the south, so the garden is somewhat shaded by the house during growing hours. That said, the radishes and the lettuce pictured above are doing great, but the beets and chard are growing very, very slowly. So far it’s been successful and last night we had the first salad using the lettuce.