We don't heat our polytunnel, at 60-28ft it is far to big to heat, starting from around a month ago we have begun to reduce watering and we will now not water till it begins to warm up, usually February time.
Most of our plants are on the floor of the polytunnel, these are then raised off the ground by placing trays underneath them, this ensures they have good drainage and airflow through the cooler months.
Keeping the plants dry will really help them cope with the cooler temperatures, we do have horticultural fleece that we will use during extremely cold spells but luckily down in Devon where we are based we avoid the worst of the weather.
Airflow is a really important factor to consider even in a small cold frame, if possible you should air your plants as much as you can, by providing good spacing amongst them and opening the vents/doors on the greenhouse or polytunnel. This is essential to avoid mould, mildew or botrytis in your plants.
In particular Echeveria can be sensitive to water droplets landing on them from above, Cante and Lauii being our main culprits! These are put at the rear of the bench and later in the winter within the cold frame to stop any drips that can cause them to rot over winter.
This time of year we are still potting on certain plants but if you are further north it will be best holding off till spring. Over winter make sure to check your plants for any damage or dead leaves that could become mouldy and threaten the whole plant.
If you have any questions please let us know, we are always happy to help.