As the temperatures drop, tender plants such as citrus trees and bananas ideally need to be brought inside. But hardy outdoor plants may also need some protection from frosts, and plants in containers will be particularly vulnerable as their roots only have a small layer of compost to protect them from the elements. Terracotta pots are also susceptible to cracking in cold weather: many absorb water, which can expand when frozen, sometimes causing the pot to crack.
You can go some way to keeping your container plants protected by keeping them in a sheltered area and grouping them together. Wrapping pots in bubble wrap or hessian will also help. Alternatively, you could invest in a protective pot cover or jacket. A more attractive and user-friendly option, these are particularly useful for plants like bay standards kept outside a house and hard to move.
There are various companies producing these insulating covers which come in a range of larger sizes from around 40cm wide. The jackets or bags are made of waterproof breathable fabric in colours from black to terracotta and the inner layer is made of insulating materials such as bubble packaging, bubble foil, or aluminium film for thermal insulation. Some have a Velcro or zip fastening and may include a draw string to adjust the size of the opening for extra protection. The base of these jackets are made of an insulating material, such as polystyrene, with drainage holes and materials like coconut pads often adding extra insulation. Coconut pads can also be used on the crown of the plant.
To protect the plant and other plants in the ground against frost, horticultural fleece draped over the plants and bushes is a good temporary solution, helping to keep snow off them. You can also buy frost covers of different sizes made of fleece with a draw string: another good investment for the winter to keep your plants toasty.