How to Remove Green Mildew from a Deck

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how to remove green mildew from a deck

If you’ve noticed green spots on your deck, it’s likely mildew caused by dampness. 

You’ll be glad to know that getting rid of these green marks is super easy to do, and you probably have the necessary supplies in your kitchen cabinet.

How do you Remove Green Mildew from a Deck? Use white distilled vinegar. This works whether your deck is composite or wood. Start by filling a spray bottle with vinegar. Now, spray the mildewed areas on the deck. Allow this to sit for one hour and then scrub with a soft-bristled brush. Follow up by thoroughly rinsing the area.

The 5 Best Ways to Remove Green Mildew from a Deck

5 best ways to remove green mildew

Power Washer

If you have a power washer, you can use it to remove the mildew from your deck. You’ll want to use the lowest setting possible that still provides you results. The pressure should be between 500-1200 psi, depending on your deck’s material.

With the lowest setting that works and a tip with a 40-degree spread, hold the power washer about two feet from the deck, and spray the mildewy spots. 

The power from the pressure washer will remove the mildew. However, you may need to go over your entire deck to achieve an even-looking result.

Mold & Mildew Deck Cleaner

Another great option is to use a deck cleaner. Cleaners like Mold Armor Deck Wash are extremely easy to apply and kill mold, mildew, and algae.

All you need to do is put the solution in a pump-up sprayer, lightly spray your deck, allow the solution to sit for ten minutes, and then rinse off. 

Baking Soda

Baking soda is mildly abrasive, which makes it helpful for scrubbing mildew off of a deck without taking off the finish or bits of wood.

Here’s what to do:

  • Put one cup of baking soda into a gallon of warm water
  • Dip your scrub brush in the mixture
  • Scrub the mildew
  • Rinse with a hose


Vinegar is an excellent mildew and mold remover for the deck since it’s high acidity helps it kill mold at its source. However, the problem is that since vinegar is highly acidic, it can eat away at its finish.

If your deck is composite or unfinished wood, vinegar is safe to use. Here’s what to do:
  • Put vinegar in a spray bottle
  • Spray the mildew and allow the vinegar to sit for one hour
  • Scrub it with a soft-bristled brush
  • Thoroughly rinse with your hose


Oxiclean is another excellent choice for dealing with mildew and cleaning a deck. It’s a much safer alternative than chlorine bleach.

Here’s how to use it:

  • Mix one cup of Oxiclean to one gallon of warm water
  • Dip your scrub brush in the mixture and scrub the mildewed deck
  • Rinse off with a hose

How to Prevent Green Mildew from Coming Back

As the saying goes, an ounce of prevention is worth a pound of cure. And when it comes to green mildew, moss, or algae, prevention isn’t too hard.

This mildew forms in dark, damp environments. The best way to stop it is by keeping leaves and debris swept off of your deck. Also, if there are any spots in the deck that sag and hold water, replacing those boards can help.

Frequently Asked Questions

faq how to remove green mildew from a deck

Why is my wood deck turning green?

If your wood deck is turning green, it’s likely from algae or green mildew. Green mildew develops in wet, dark places. So, if your deck has been wet for a prolonged period or you’ve failed to remove leaves and other debris, you’ll start to see this mildew form.

How do you get green algae off of a composite deck?

You can get green algae off a composite deck by scrubbing the area with white distilled vinegar and a soft-bristled brush. Alternatively, you can power wash the algae.

Can I use Dawn to clean my deck?

It’s perfectly safe to use Dawn to clean your deck. It may even help remove mildew as long as you use a scrub brush. All you need to do is add a little dawn to some warm water and scrub your deck. Rinse with a hose afterward.


When removing green mildew from a deck, you have plenty of options. You can go the commercial route and try a product like Mold Armor which will remove algae, mold, and mildew, or use a household cleaning agent like vinegar or OxiClean.

Mildew is easy to remove from decks, and any of these methods will yield positive results.

Photo of author


Katie Barton lives with her husband and three daughters in an 1800’s style log cabin in southern Ohio. She thinks cleaning is relaxing and is considered the organizing go-to person by her family and friends. She runs the blog Cabin Lane where she shares about cleaning, decluttering, and minimalism. See full biography here.

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