Pressure washers are the quickest and most popular method for cleaning green mold on decks. However, it is also easy to damage the wood and finish on a deck with a pressure washer. One solution is to scrub the deck by hand and only use a garden hose and a high-pressure nozzle to rinse the deck. This is a more time-consuming approach but it protects the deck. Another alternative is to only use a pressure washer to rinse the deck. Scrub the deck by hand and use the pressure washer, rather than the garden hose, to rinse the deck. This will do a more thorough job than the garden hose but it is important to test the pressure washer to make sure that it is not damaging the deck.
Remove all furniture and other items from the deck. Sweep the deck with a broom so that the surface is clean of all leaves and other sorts of debris.
Develop a strategy. Decide in what order to proceed. Work on one section at a time. Don't back yourself into a corner and avoid walking across sections that you have already cleaned.
Apply oxygen bleach to a section of the deck with a scrub brush. Most household bleaches are chlorine based, but oxygen bleach is nontoxic and environmentally safe. It won't harm plants, flowers or trees and you won't suffer from the fumes. Oxygen bleach comes in powder form. Read the instructions and mix the proper amount in a bucket with warm water. Oxygen bleach forms bubbles that soak into and clean the wood. Dip a scrub brush into the bucket and clean a section of the deck. Allow the bleach to soak for a few minutes.
Test the pressure washer. Start with an inconspicuous area. Pressure washers use different tips that concentrate different amounts of pressure. The tips are color coded depending upon the amount of pressure. Use the white tip, which is 40 degrees, to rinse the deck. Hold the pressure washer tip about 18 inches above the deck area and rinse it. Inspect the wood to make sure the pressure washer isn't doing any damage. Switch to a garden hose if the pressure washer is damaging the wood.
Rinse the bleach off of the first section. Inspect it to make sure that it is clean. Continue with the next section. Repeat the process until the deck is completely clean.