>>1401801That's pretty normal.
You have those in outdoor poly tunnels right? Do you have a thermometer inside it? Put some extra thermal mass in with them. It can be stacked under them so long as it is protected from outside wind and included in the air circulation inside the cover. A reflector can be placed flat on the ground in front of the entire unit to help bounce light to the thermal mass and heat it up a bit better. The thermal mass is optimally black-painted containers of water, but since the temps are so close to freezing it may burst them if the temps drop extremely. Instead you can just fill the containers of soil or sand. Like you can have a few buckets full of the stuff that your lettuce until can sit on and everything be draped with the plastic film. That would be a simple version of the ones in this image.
