Plastic garden furniture should be able to tolerate damp, wintry conditions, so it can be left outside year-round. Plastic furniture can also fade when left out in the sun, so it's a good idea to cover it in the warmer months as well. Rattan furniture may be weatherproof, but cushions for garden furniture are not. While not in use, the cushions should be removed and stored indoors. Leaving them outside will result in them becoming dirty and damp, and will never be comfortable to use.