There is no straight answer about when to start protecting your plants. It can depend on your type of plants, the area it will be standing in over winter and finally your local climate. For instance, you could be living in a small micro climate or in a frost pocket.
Bubble wrapping the outside of pots if you don't have a second pot as insulation. Some people pot into a larger sized pot to create extra protection. The gaps could be filled with brokened down used polystyrene packaging to minimise freezing pots. Keeping pots together or up against a warm wall or southlerly wall is always best but if not, the fleece can be doubled up for extra protection.
Non-woven material is the ideal fleece as it still allows air getting through whilst keeping out frost and giving protecton. I have been recommended to try Poundland's Dust Sheet which uses the exact same material but much cheaper, just cutting to size what you need. It is not necessary to open up the fleece every day, but it is still essential your plants get some light, so when temperatures ease up, do open up the allow more air and light to minimise any rotting and encouragement of fungal diseases.
See original post
Thanks for the tip about the dust sheet.