Plastic and Vinyl Furniture
For plastic furnishings, mix a little dish soap, some borax and half a cup of peroxide into one gallon of water. Let the mixture sit for 10 to 15 minutes, and use it to scrub all your plastic outdoor furniture with a nylon brush before rinsing well. Test a small area first to be sure the peroxide does not react negatively with the furniture.
If winter's cold, wet and damp weather has left your wood furniture covered with mildew, you'll need to start with a thorough cleaning using an oxygenated bleach like Oxi-Clean or a solution like Jomax. Just like the plastic procedure above, test first, then apply the solution and let it sit for a while. Then, scrub and rinse it away. If you have one, a pressure washer can help with this job, but be careful to use it on the very lightest setting, as too much force will ruin your wood. Also, be careful not to let any of bleach-based cleaning solution get on your cushions or you'll find yourself in need a new decorating scheme to match the white spots!
After the furniture dries thoroughly, oil the wood surfaces with a sealant or preservative that is appropriate to the material. You can clean the furniture a couple of times a month with an oil soap.
Metal furniture is easiest to clean, using just soapy water and elbow grease. I find that soaps designed for washing your car work well at cleaning away the grime. If you find any rust or stains, you can clean those with a fine-grit sand paper and touch up the worn area with paint. For badly rusted furniture, you can sand thoroughly and then repaint the entire piece with a rust-prohibiting paint.
Periodically cleaning your furniture throughout the summer is the best way to avoid the need for a major preseasonal cleaning next year. Also, avoid letting pollen or bird droppings sit on it, and cover furniture up if you won't be using it for a while.
Finally, keep in mind that exposure to sunlight is a great, natural way to keep furniture clean. Sunshine stops moss and mildew from growing, so occasionally move furniture kept in shady areas into full sun and let nature do its work!
Got more stuff to clean? Get more home cleaning tips from Tom Kraeutler at MoneyPit.com.