How To Remove Green Algae From Wooden Deck

If you’ve put a lot of work into building and maintaining a wooden deck, spotting green algae or mold growing on it can be incredibly disheartening.

This algae growth makes your deck look filthy and leaves a slippery film, making your deck a hazardous place to walk.

There’s some good news, however.

Wooden decks developing green algae, fungus, and mold is common and can be easily fixed.

While it’s possible to remove the algae from the deck, there’s no way to fully prevent it from coming back again. This is just one of the issues homeowners face with wooden decks. Fortunately, proper care and maintenance can keep the algae at bay to some extent.

Be sure to complete this task at least once a year. Otherwise, the green algae and mold can rot the boards of your deck. This will create far more work in the long run than annual preventative maintenance.

Today, we’ll show you how to remove green algae from wooden deck along with a summary of the most effective tools to strip it away with.

Don’t wait until someone takes a tumble before you take action. See how to remove green algae from wood deck today.

Preparing the Deck

The first thing you need to do is thoroughly clean your deck.

Remove everything from the surface including any furnishings, plant pots, and BBQ grills.

Using a regular broom, thoroughly sweep your wooden deck. Be sure to get the edges where the deck meets the house as well as the point where the railings touch the deck. Remove as much dirt and debris as you can. If you have a leaf blower, you can use this to clean the debris off the deck faster.

You can opt to rinse the deck with a garden hose at this point. You could also use a power washer. Sometimes, a first cleaning may remove most of the algae and it may look like the problem is solved but keep at it– a small, invisible layer of algae may remain and it will grow back quickly.

Cleaning the Deck

The best way to remove green algae from a wood deck is with a high-quality deck cleaner. These products are used to loosen dirt that has been ground into the wood fibers. They also help to remove other debris and gunk from the deck’s surface. There are plenty of different deck cleaners on the market, and you should choose one that’s specifically designed for treating mold or green algae. This will be more effective than an all-purpose cleaner.

The best deck cleaners that we’ve used are oxygenated bleach wood cleaners and a power washer. Some recommend using chlorine bleach, but this could damage your wood and will certainly kill any vegetation surrounding your deck. An oxygenated bleach deck cleaner like #1 Deck Wood Cleaner won’t damage your wood and when it’s diluted, it won’t harm any surrounding plant life.

Start by getting the deck wet with a hose. This is an important step. Wetting the deck fills the pores with water so the cleaner will remain on the surface of the wood, where it needs to do the most work. Skipping this step will result in the cleaner soaking deep into the pores, which means it’s going to take longer to rinse the product out of the wood.

Once the deck is wet, mix a 2.25 lb container of wood cleaner with a 5 gallon bucket of water. If possible, use luke-warm water. This is the perfect activation temperature for the cleaner, causing it to dissolve more completely. Using cold water may take longer for the wood cleaner granules to activate and dissolve. Using water that’s too hot will cause the cleaner to activate too quickly and lose its effectiveness. Luke-warm water will give you the best results. Don’t worry, you can still use cold water, you just may need to stir it a little longer and wait a little longer for the wood cleaner to dissolve.

Ok, so your wood cleaning solution is dissolved and ready to use. You can apply this to your wood either with a pump-up garden sprayer, a mop, or a deck brush (this deck cleaning brush works extremely well).

If you use a pump-up garden sprayer, make sure to pour the cleaning solution through a paint strainer sock to prevent any undissolved granules from clogging your sprayer tip.

Allow the deck cleaner to remain on the deck for 15-30 minutes so it kills any remaining green algae or mold. Keep the wood wet with additional cleaning solution if it starts to dry out. If it dries, it will stop working. Allowing the wood cleaner to remain on the deck during this time will loosen up any old finishes as well as remove any graying, mold or mildew. Once the cleaning solution has had time to work, it’s best to rinse the deck with a pressure washer. This is the best way to bring an old wooden deck back to life. The wood cleaner will clean and loosen any old finishes and the pressure washer will remove what the wood cleaner loosened up. If you don’t have access to a pressure washer, you can always use a stiff bristle brush and some elbow grease. However, this will not be as effective as a pressure washer. When using a pressure washer, just be careful not to get the nozzle too close to the wood as this can damage the wood fibers. Also, make sure your pressure washer isn’t more than 1200 psi.

Also, if you plan to re-stain the deck after removing the green algae, you should definitely use a two-step cleaning method to ensure there’s no algae trapped under the new stain. The best way to do this is to apply a wood brightener. The wood brightener can be applied immediately after the wood cleaner, and will neutralize any remaining cleaner on the surface as well as brighten the wood so that it looks new again. See the photo below to see what a difference brightener makes.

Rinse the surface of the wooden deck again with a garden hose to remove any brightener that has been left behind. Be sure to rinse the rails, steps, and any other surface where the brightener might have splashed. For this step, a garden hose works better than a power washer. You’ll want to rinse the deck with as much water as you can. A pressure washer will add air, and use much less water than a garden hose, so just give the deck a thorough rinsing with the hose.

Once the deck has dried out completely, inspect it once more to be sure you removed all the green algae. When you are satisfied, you can put all the furnishings, plants, and other fixtures back where they belong.

If your deck seems prone to green algae build-up, you can clean your deck annually with this cleaning method to keep your wood looking great year round. You may consider staining your deck with a semi-transparent deck stain that will give it a nice finish as well as seal it to help prevent future mold and mildew growth.

Deck Cleaners for Green Algae

We’ll finish with a quick look at 3 of the best deck cleaners for dealing with green algae.

#1 Deck Wood Cleaner

This cleaner has been specifically formulated to work on outdoor wooden surfaces including decks, fences, siding, and can even be used on vinyl siding, aluminum siding and more.

Its core purpose is to deep clean wood surfaces, remove mold, mildew, and green algae.

Simply mix it with water and spray it or mop it on the area that needs cleaning, let it sit for 15-30 minutes then pressure wash it off.

The cleaner is biodegradable, and the compounds break down safely in soil.


  • Very effective
  • Extremely easy to use
  • Concentrated formula goes a long way


  • Must use a power washer to rinse


#1 Deck Wood Brightener

This oxalic acid cleaner from #1 Deck is great for making wood surfaces look bright and new. It’s the second step in the cleaning process and will really make your exterior wood look new again.

This concentrated formula goes a long way and only takes about 5 minutes to work. This cleaner will neutralize the surface of wood and make it ready for staining.


  • Extremely fast acting
  • Amazing results within 5 minutes
  • Concentrated formula with super coverage


  • Has a somewhat strong cleaner smell


Restore-a-Deck Wood Cleaner

One of the more popular cleaners on the market, Restore-a-deck wood cleaner contains no bleach or any any other caustic chemicals.

This cleaner is perfect for multiple surfaces and won’t cause any harmful reactions. When looking at how to remove green algae from wood deck, this fits all the criteria.

It will remove moss, mold, mildew, and green algae.


  • Simple to use
  • No caustic chemicals or bleach
  • Safe for multiple surfaces


  • Can darken certain wood types (if this happens the Restore-a-Deck Brightener will lighten it back up)

  1. Just treated my deck with Restore a Deck kit. It is old so I had to use 50% bleach in addition to the 2 components. Will use #1 next time.


  2. […] Water based stains are not a food source for mold, mildew and algae and minimize their growth potential. Stains containing zinc nano-particles, such as DEFY Extreme and Behr, will have a better natural resistance to mildew growth. […]

  3. […] and tables that will be outside permanently; as they also contain an anti-fungal element which prevents mold and algae. These stains will penetrate the wood and form a bond with the wood fibers, protecting the wood […]

  4. […] It dries quickly and offers superb protection from mold and algae growth. […]

  5. […] This solid deck stain is an outstanding acrylic stain from DEFY.It is made of zinc Nano-particles whichmakes it a UV resistance against the color fade, Additionally, It uses the greatest and latest in resin technology which hasa lifespan of 5-year minimum without degrading or peeling. It penetrates your wood well and eliminates the likelihood of peeling. It will dry fast and provides superb protection from algae and mold growth. […]

  6. […] good quality deck cleaner is essential if you are wondering how to remove green algae from wood deck. The best thing about these cleaners is that they help in loosening all the dirt and debris from […]

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