7 Easy Ways How to Remove Green Mold From Wood Deck

Is your deck turning green? Are you tired of slipping on slimy mold and worried that it is going to destroy your deck? Need to know how to remove green mold from wood deck boards?

Remove green mold from wood decks using a pressure washer or a long-handled broom and cleaning solution. Wet it, wash it, and scrub where necessary, and then rinse it thoroughly. Alternatively, try a mold-mildew-algae stain remover and let it do the work or one of the many homemade wood deck cleaners.

In this article, we’ll discuss what green mold is, whether it’s dangerous, what causes it, and how to remove it from a wooden deck. By the end of the article, you should understand how to remove green mold and protect your deck from damage.

How to Remove Green Mold From Wood Deck

What Is Green Mold on Wood

Green mold growth occurs commonly on wood in shady or damp moist areas, or under debris that creates a shady, damp area. It often begins as dark spots or ‘shadows’ before becoming furry or fuzzy. Mold can appear in different colors depending on the type of mold, environmental factors, and sometimes on the content of the material, it is feeding on.

With over 100,000 different types of mold or fungus living and working to break down organic materials, identifying the exact species requires an expert. Green mold includes thousands of different species. Penicillium, Cladosporium, and Aspergillum classifications of mold can all have a greenish coloring, as well as other colors.

Green mildew on deck boards may not be mildew; it might be mold. Mold isn’t mildew, although both are fungi and can occur together on different surfaces. Green mold ranges from greenish to black and is usually slimy or fuzzy. Mildew usually begins as yellow spots and then turns grayish white to a brown or greenish tinge, and has a powdery or fluffy texture. Mold penetrates wood or other organic material, not just on the surface. Mildew stays on the surface and spreads across it. Although not the same, they grow in similar damp, dark conditions.

Is Green Mold Dangerous?

Green mold on deck surfaces may be less worrisome than if it was growing in your basement or bathroom, but it is still a health hazard. Mold releases airborne spores that affect those with asthma, allergies, and other respiratory concerns. Decks are often located near homes, and mold spores can easily drift through screens and into homes to affect your family.

Mold can cause headaches, rashes, nervous-system disorders, and some types are linked to blood poisoning (sepsis) and even brain infections. It has also been linked to cognitive concerns like memory loss, depression and mood swings, dizziness, and fatigue. Green mold is toxic, and while it may not kill you, it can seriously affect your health.

What Causes Green Mold

Mold is a fungus and helps to decompose or break down organic material, like wood. Mold spores are present almost everywhere, and in the right conditions, they can settle in for a feast and thrive. Mold grows best in damp, shaded or dark environments, like basements, attics, and bathrooms. So, why is growing on your deck in the great outdoors?

Wood decks are an organic material, which means mold will naturally be attracted to them, and if the conditions are right, it’ll thrive. Outdoor decks experience the full spectrum of climatic conditions and may spend weeks or even months being damp, especially if they haven’t been maintained and sealed or stained regularly. Anything that offers a shade that prevents sunlight from penetrating and drying the wood provides an ideal ‘home’ for mold to grow.

Leaves, planters, BBQ covers, furniture, and even lattice screens provide shade and can keep wood from drying out. Trees and shrubs may also create seasonal shade, as can fall leaves left to decompose on the boards. Airflow over and under a deck helps dry the wood and prevent mold growth on the top and underside of the planks. So, if you don’t want to remove green mold from deck surfaces every year, make sure air or sunlight can reach as much of the deck surfaces as possible.

How to Remove Green Mold From Wood Deck

Green on wood deck boards would not be a good sign, especially if the wood didn’t start that color. The green tinge may be caused by mold, mildew, algae, or moss on deck surfaces. Regardless of what it is, you’ll want to clean it off before it can cause damage, expensive repairs, and health issues.

Many products or concoctions for removing green mold from wood deck boards will also remove mildew, algae, and moss. Here are different ways to clean green growth off your deck.

1. Pressure Washer

Remove algae from deckOn a small deck or one where a pressure washer isn’t practical, use a scrub brush on a long handle and a bucket of cleaning detergent mixed in water. Use a pressure washer with detergent on a large deck to clean the mold off. You can rent or borrow a washer if you don’t have one. Remove everything from the deck – chairs, planters, BBQ, toys, everything – and then sweep it clear of any leaves, sticks, or debris.

Review the owner’s manual when adding a cleaning solution or detergent to the power washer. Use the nozzle recommended for dispensing soap. Apply the solution in a sweeping motion across the planks starting at the farthest side or corner. Wash the whole deck thoroughly. Use the scrub brush in awkward areas and where mold is present.

With the deck washed and scrubbed, change to the widest nozzle setting or attachment. Hold the nozzle 18 to 24-inches from the deck surface and wash it using a sweeping motion going with the wood grain. After the second wash, thoroughly rinse the deck with clean water to remove all cleaning residue. This is one of the best methods on how to clean moss off decks, as well as removing algae, mildew, and mold.

2. Mold Mildew and Algae Stain Remover

How to remove green mildew from deckMany products take mold and mildew from decks. There are fewer, though, that do mold, mildew, and remove algae from wood deck boards, and fewer still that will also clean moss off decks. One well-reviewed product is Wet & Forget moss, mold, mildew, and algae stain remover.

Some products are EPA certified for use around gardens, plants, and other landscape features. However, they shouldn’t be applied near water sources, rivers, or lakes. The concentrated formula is diluted following the manufacturer’s instructions. For some products, one-gallon makes 6-gallons, so one part product to 5 parts water and the 6-gallons treats up to 1200 ft². It should be applied using an attachable hose spray bottle, pump-up sprayer, bucket and mop or broom, or a hand-held sprayer for small spots.

Wet & Forget products contain no bleach and aren’t acidic or caustic. They should be applied on a morning with mild temperatures and no chance of rain for at least four hours. Spray or mop the solution on, and you’re done. There is no rinsing or scrubbing needed. Dark or extreme stains should receive a second soaking 4 to 5 weeks later.

Note: For quicker results with moss or thicker organic stains, remove as much of the material as possible without damaging the deck surface. A pressure washer may prove helpful. Apply the diluted stain remover to the surface once the top layer has been removed.

3. Chlorine Bleach

Deck algae cleanerMold and mildew are a fungus, which means they are plants, not dirt. Mildew is a surface plant that eats across the surface. Mold isn’t only on the surface of the deck boards; it works its way into the cell structure and begins to decompose the wood. Just wiping them off the deck won’t get rid of mold and mildew. Like poison ivy, they must be killed, including their ‘roots’ in the wood.

There are many products with EPA approval for eradicating mold and mildew. Chlorine bleach has been used for years to remove mold and mildew, but due to environmental concerns, its outdoor use is discouraged. Bleach works well on non-porous surfaces. However, it shouldn’t be used on wood. While it will destroy the fungus, it also damages the lignin (organic polymers) that binds the fibers together. So, it not only destroys the mold and mildew; it damages the wood too.

An alternative to chlorine bleach is oxygen bleach. It kills bacteria and destroys fungus, is non-toxic, biodegradable, and safe for the environment. Combine 1 cup oxygen bleach to 1 gallon of warm water, 1/2 cup of borax, and 1/8 cup of dish soap. Apply it with a pump sprayer, spray bottle, or mop and bucket. Use a scrub brush to work it into the wood, let sit for 15 minutes, and rinse thoroughly. After cleaning the deck, it will require a brightener to restore the wood luster, neutralize the oxy bleach, and restore the natural pH of the wood.

4. Hydrogen Peroxide

Removing green algae from woodHydrogen peroxide (3%) is an environmentally friendly choice for cleaning mold and mildew off a deck. Mix the hydrogen peroxide with an equal amount of water in a spray bottle. Spray it on the mold and mildew and let it sit for 10 minutes. Wipe it off with a sponge for small areas, or rinse it off with fresh water on large areas. Make sure to keep away from clothing and fabrics as it acts like bleach.

When cleaning moss off wood decks, use concentrated (25-30%) hydrogen peroxide in a spray bottle – don’t dilute it. Wear gloves, mask, and eye protection and spray the peroxide directly on the moss. Saturate the moss and let the peroxide work. Once dry, scrape or pressure wash the moss off. A second application may be required to kill the roots of the moss. After removing the moss and cleaning the deck, apply a brightener to restore the wood luster, and restore the natural pH of the wood.

5. Baking Soda

Green mildew on deckBaking soda isn’t a harsh chemical but can be used to scour stains and blemishes off surfaces. Mix a cup of baking soda in a gallon of warm water and apply it with a scrub brush to remove green mold from the wood.

Work the solution into the wood with the brush to lift the fungus out of the wood. The mixture can be used to wash the whole deck, or just applied to the moldy areas. Rinse with fresh water when done.

6. Clean Deck With Vinegar

White vinegar is acidic and will seep into the wood and wipe out the mold at its roots. Mix the vinegar with an equal part of water and pour it into a spray bottle or plastic watering can. Apply it liberally to the whole deck as a cleaner, or only to the mold or mildew areas. If the mold area is large, do a section at a time, so the vinegar solution doesn’t dry. Use a stiff-bristle scrub brush or broom to work it in and to remove the fungus. Rinse the wood thoroughly with clean water.

7. Homemade Wood Deck Cleaner

There are many homemade deck cleaning recipes available. Some work better than others, and some are an environmental hazard like chlorine bleach. Arguably, vinegar, hydrogen peroxide, baking soda, and oxygen bleach are also homemade solutions. However, they also kill mold and mildew, while other homemade cleaners won’t.

No products found.To clean a wood deck, dissolve 1 cup of laundry soap in 3 gallons of warm water. The type of laundry soap is important if you need to kill mold or mildew. Select a product that states it kills or removes the fungus as well as dirt and grease. Use a pump-sprayer or bucket and scrub brush to apply the mixture. Scrub it into the affected boards to remove the fungus. Rinse the deck thoroughly when done.

A homemade deck cleaner that will clean algae off wood decks, as well as mold and mildew, is a solution of 1 cup of No products found. (TSP) in a gallon of water. The mixture forms an alkaline solution, so gloves and eye protection are recommended. Apply with a bucket and brush or pump sprayer. Scrub with the grain if possible to avoid lifting or ‘furring’ the board surfaces. It may take more scrubbing effort to lift the algae or mold out of the wood. When the surface is clean, rinse it thoroughly with fresh water.

How Do I Stop Algae Growing on My Deck?

To prevent algae on wood deck surfaces, you need a good airflow over and under the boards to help them stay dry or dry after a rain. Algae, like mold and mildew, flourishes on warm, moist surfaces. Using deck algae cleaner is only one of the ways of how to remove algae from wood decks. Using oxygen bleach, vinegar, or hydrogen peroxide, or TSP solutions will also remove algae from the deck boards.

Scrape the surface foliage off first without damaging the wood. Apply the cleaner as per its directions, or the other solutions using a pump sprayer or scrub brush. Work it into the wood in the direction of the grain. Once the algae are gone, rinse the wood thoroughly with clean water.


Removing unsightly green mold, mildew, moss, and algae from your wooden deck is necessary to protect the wood and your investment. It also makes the surface safer to walk on and is healthier for those who enjoy relaxing on it. Regular cleaning and improved airflow will help keep the green mold off the deck. Applying stain or sealer to the wood will keep the moisture out of the wood pores and prevent the growth of mold, mildew, algae, and moss.

I hope you understand what mold is, why you don’t want it on your deck, and now know how to clean green mold off wood deck surfaces. If the article proved interesting or helpful, please share it with others. As always, your comments and suggestions are appreciated.

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