How to Remove Algae From My Deck

Updated March 17, 2017

Algae is a green plant that forms on decks that have been exposed to humid conditions or have been treated with an oil-based sealer. The algae on the deck is a green discolouration that can spread if left untreated. To remove the algae from your deck you can choose to power wash the deck with high-pressure water or use a deck cleaner containing bleach to kill and wash away the growth. A combination of the two processes helps ensure the algae has been destroyed.

Clear all furniture, plants and rugs off the deck.

Sweep the deck using a heavy broom. Work around the algae area to make sure all debris has been brushed away.

Put on a pair of rubber gloves. Combine 2 cups of oxygen-based bleach to 1 gallon of water in a plastic bucket and pour the solution into a plastic garden sprayer.

Hold the nozzle of the sprayer wand 12 inches above the stain on the deck. Squeeze the trigger on the garden sprayer to coat the algae with the bleach solution. Wait 10 to 20 minutes.

Scrub the area with a scrub brush or push broom. Spray the area with a garden hose, rinsing away all bleach from the area. Allow the spot to dry. Repeat if there is any remaining algae on the area.

Clear all furniture, plants and rugs off the deck.

Equip the power washer with a 40-degree spray nozzle and set the washer pressure to 1500 PSI. Do not use a nozzle with a smaller number or set the power washer pressure above 1500 PSI as this can damage your deck.

Point the nozzle up and away from the deck. Squeeze the trigger to begin spraying.

Bring the nozzle down and across the deck in a sweeping motion. Keep the nozzle about 2 feet away from the deck at all times.

Spray back and forth across the algae on the deck until the green discolouration is gone. Allow the deck to dry.


Seal your deck once it is completely dry.

Things You'll Need

  • Broom
  • Rubber gloves
  • Oxygen-based bleach
  • Bucket
  • Garden sprayer
  • Scrub brush
  • Power washer
  • Power washer spray nozzle, 40-degree
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About the Author

Dan Chruscinski has written pieces for both business and entertainment venues. His work has appeared in "Screen Magazine" as well as websites such as Chruscinski graduated in 2006 with a degree in English literature from Illinois State University.