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What Are Those Greenish-Black Stains on My Wood Deck?

By Wet & Forget

You’re planning an outdoor party, and you notice ugly greenish-black stains on your wood deck; what is it, and how do you clean it?

Here, we’ll cover what it is, what causes these growths, and how to clean a wood deck with Wet & Forget Outdoor products to erase ugly deck stains.

What is it?

If you see green and black stains appear on your deck, it’s probably algae. Green algae can grow on any damp and shady surfaces around your home, such as a deck. Black algae will grow in either sun or shade.

Both are algae types that can ruin your deck’s appearance, creating a slipping hazard. Algae left untreated can damage your deck and other outdoor surfaces.

Natural wood and synthetic decking are equally susceptible to stains caused by mold, mildew, moss, and lichen.

Photo of clean wood deck.

Why does algae grow on outdoor surfaces?

Algae are microscopic organism that produces spores that are spread by the wind and rain. Unfortunately, algae grows fast, appearing as slimy, greenish-black stains on outdoor surfaces, one example being a deck.

Algae thrives in outdoor locations where moisture, humidity, and shade are present.

Which Wet & Forget product should I use to clean my deck?

Wet & Forget Extreme Reach™ Outdoor Hose End eliminates ugly algae, lichen, mold, and mildew stains on all deck types, including natural wood, synthetic, composite, metal, and vinyl, with no scrubbing, pressure washing, or harsh bleach required!

Wet & Forget Xtreme Reach™ is a gentle, pH-neutral formula that starts cleaning with the wind and rain to remove growths and stains over time. And it keeps them from coming back for a year or more in most cases.

Wet & Forget is also bleach-free cleaner.

Finish up your fall cleaning checklist by applying Wet & Forget to your deck.

How do I apply Wet & Forget Outdoor to a wood deck?

Wet & Forget Xtreme Reach™ gets rid of ugly deck stains caused by algae, moss, lichen, mold, and mildew stains. It’s economical, easy to apply, and takes the guesswork out of deck cleaning.

Algae tracked inside can stain your carpeting. Plus, algae can grow to create a slick surface, which is dangerous to walk on.

How to clean a wood deck with Wet & Forget Xtreme Reach™ Outdoor Hose End
  • Attach the nozzle to your garden hose.
  • Attach the fan tip to the sprayer.
  • Turn on the water.
  • Turn the black dial on the sprayer to the “ON” setting.
  • Spray the surface thoroughly with Wet & Forget Xtreme Reach™ Outdoor Hose End cleaner.
  • Allow the deck to dry for a minimum of 4 to 5 hours before use.

Just spray Wet & Forget Xtreme Reach™ Hose End on your deck and walk away. You’re done! Let Wet and Forget clean the deck for you – no scrubbing or pressuring washing required!

Retreat your deck annually or at the first sign of re-growth. Timing may vary according to your region and weather conditions.

A note about natural wood decks: We recommend sweeping and cleaning off the surface with a stiff broom approximately one month after application. This will lift and remove dead growths from the surface.

Bonus Application Tips

Check the weather for chances of rain before applying Wet & Forget to a deck. For best results, 4 to 5 hours of drying time and no rain are required.

The best time to apply the product to a deck is on a cool and cloudy, overcast day or in the early morning. This gives the product plenty of time to penetrate the deck surface and start cleaning and eliminating ugly growths.

Will Wet & Forget Outdoor clean my Outdoor Furniture?

Wet and Forget Outdoor will remove moss, mold, mildew, and algae stains from patio furniture. Spray the furniture with our Wet & Forget Ready-To-Use and let sit overnight. The next day, come back and rinse the surface down with water.

Be sure to keep any people or pets off of the furniture during application and overnight until fully rinsed off.

To utilize this product, pull out the 3-foot-long tube connected to the sprayer. Press the tip at the end of the hose into the cap and turn the sprayer to the fan setting. After that, spray the surface and allow it to dry.

Learn how to clean patio furniture, including adirondack chairs!

Will Wet & Forget clean my wood fence?

Yes. Wet & Forget Concentrate is an easy spray-on-and-leave formula that works with Mother Nature to eliminate ugly stains on wood fences. The formula cleans the fence for you – no scrubbing or pressure washing is required!

Wet & Forget Concentrate is perfect for surfaces such as wood fences, concrete steps, and sidewalks.

The cleaner comes in gallon and half-gallon bottles. The gallon bottle can cover up to 2,250 sq. ft.

Mix 1 part Wet & Forget Concentrate with 5 parts water into a pump sprayer.

Spray the fence, thoroughly saturating the surface, and then just walk away. After a few weeks, your surfaces will clear up, and the stains will be removed.

Allow the fence to thoroughly dry before sanding, painting, staining, or sealing.

Discover how to clean a fence by following our guide.

Bonus Tips
  • Painting, staining, or sealing your wood fence can help prevent deterioration.
  • An oil-based stain will add beauty and highlight the wood’s natural grain. Re-stain your fence approximately every 3 years.
  • A wood sealer adds a protective barrier, protecting the wood from water and harmful UV rays. Reseal your fence once a year.

Learn more about Wet & and Forgets powerful cleaning products. Use our Store Locator to find Wet & Forget products at a store near you.

Or give us a call at 888-727-8524, M-F 8:30 a.m. – 5 p.m. CT. We’re happy to answer any questions about the products you may have.