How to Deep Clean Mold and Mildew from a Wooden Deck

Decks are natural sponges for moisture, and when the seasons turn, mold and mildew often claim the wood fibers as their own. Seeing dark spots or a green film on your boards is frustrating, but it is rarely a sign that you need to replace your decking. With the right chemistry and a bit of elbow grease, you can lift the fungal spores out of the grain without damaging the integrity of the wood. Done well, this process goes beyond just removing surface grime; it prepares the deck for proper maintenance like staining or sealing. The goal is to kill the fungus at the root while keeping your plants and landscaping safe. If you approach this with a systematic cleaning plan, you can bring your deck back to a clean, uniform look in a single afternoon.

1. Protect Plants and Clear Space. Remove all furniture, planters, and rugs from the deck surface. Cover nearby shrubs or delicate plants with plastic sheeting to protect them from the cleaning solution.
2. Expose Every Crevice. Use a stiff-bristle push broom to clear away loose leaves, dirt, and branches. Getting the surface clear ensures the cleaning solution can reach the mold directly.
3. Activate Your Cleaner. Mix oxygen bleach powder with warm water in a plastic bucket according to the manufacturer's label. Stir until the granules are completely dissolved.
4. Let Chemistry Do the Work. Pour the solution onto the deck or use a garden sprayer to coat the surface evenly. Let the solution sit for 15 to 20 minutes, ensuring it stays wet and doesn't dry out.
5. Scrub With the Grain. Work in small sections, scrubbing with a stiff-bristle deck brush in the direction of the wood grain. You should see the mildew lift away as you scrub.
6. Flush Away Every Trace. Use a garden hose with a spray nozzle to rinse the deck thoroughly until all suds and residue are gone. Do not use a high-pressure washer, as it can gouge the wood fibers.