Arrange the furniture so you can easily access all sides, pulling pieces away from walls or out from under trees. Connect a spray attachment to a standard garden hose. Turn the water on high, and then direct the jet of water at the furniture. The pressure of the water will remove the majority of dirt and residue.
Combine the following ingredients in a large bucket: 1 gallon water, 1/2 cup household ammonia, 1/2 cup distilled white vinegar, 1/4 cup mild dish soap. Stir vigorously until suds begin to form.
Dip a large sponge into the cleaning solution. Wring the sponge gently to remove any excess liquid, and then apply it to the furniture. Scrub the wood, moving the sponge in small, circular motions. For stubborn stains or stuck-on dirt, use a small, stiff-bristled brush rather than a sponge.
Rinse the soap solution from the wood by sponging it away with clear water. Wipe the wood dry with a clean towel.
Sand any discolored areas with fine grit paper. Rub the sandpaper briskly over any portions of the furniture that seem to be gray or fading. This will reveal the good wood underneath, effectively removing the blemishes.
Brush a thin coat of water-repellent redwood sealer evenly over the furniture. This will protect the wood from the elements and prevent any warping or weathering. When the first coat has completely dried, add a second layer, if desired.