How to Remove Mildew and Algae from a Wooden Fence

Co-authored by Andres Matheu

Last Updated: March 22, 2023 References Approved

Over time, wooden fences can get covered in algae and mildew. The growth generally occurs in shaded, moist locations. There are several ways you can clean the algae and mildew off a fence so that it looks better.

Method 1

Method 1 of 2:

Using a Power Washer to Remove Mildew and Algae from Wood Fencing

1
Trim and tie back plants.
2
Cover tender plants with a tarp or invert buckets over them. Remove any other obstructions.

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3
Set the power washer on a lower pressure setting such as 1500 to 2000 psi.^{[1]
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4
Stand about 2 feet (0.6 m) away from the fence and hose it down. You can move closer in for heavily stained spots but don’t keep high pressure on any spot for too long. Move the sprayer in a slow, sweeping pattern.
5
Let the fence dry if the mildew and algae disappear from the fence. If stains remain proceed to the next step.
6
Scrub the stained areas on the fence if some stains remain after power washing.^{[2]
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- Pour a solution of one part household bleach to two parts water into a bucket. There is no need to stir.
- Use a scrub brush to clean the remaining stains with the solution. Be careful not to get bleach solution on your plants.
- Repeat the power washing on the stained areas you scrubbed.
7
Check the fence and sand any rough areas.
8
Sink any protruding nails or screws and repair any damaged wood.
9
Apply wood preservative, stain or paint to the fence after it dries prevent future algae and mildew growth.^{[3]
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Method 2

Method 2 of 2:

Hand Scrubbing to Remove Mildew and Algae from Wood Fences

1
Cover plants with tarps or inverted buckets.
2
Mix a solution of one part household bleach to two parts warm water in a bucket.
3
Add a teaspoon of a mild soap that is safe to mix with chlorine bleach to each gallon or liter of water in your bucket.
4
Scrub the stained areas of the fence with a scrub brush, being careful not to get the solution on plants.^{[4]
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5
Rinse the fence with clean water. You could do this with a garden hose.
6
Let the fence dry.
7
Repair any damaged areas, sink protruding screws or nails, and sand rough areas.^{[5]
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8
Consider painting the fence with a paint that has an algae and mildew preventative in its formula.^{[6]
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Community Q&A

Question

Should I use a bleach solution or buy an algae remover?

Community Answer

It depends. Too strong a solution or too hard a brush could streak the paint and wood. You could try using a pressure washer.
Question

Could I use a bleach solution to clean a stained cedar fence?

Community Answer

Yes, provided it is a mild solution of, say, one part bleach to five parts water. Mold and Algae will absorb the bleach with the water and should die off within three to five days. Eye and skin protection are essential, and wash your hands and any other points of skin contact immediately afterward.
Question

Is there any spray I can use on a wooden fence to treat it for algae?

June Higgins

Community Answer

Spraying ‘Elbow Grease’ is quite effective for removing green algae from a wooden fence.

Warnings

Don’t set the pressure on a pressure washer too high or it will damage the fence.

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Helpful 18 Not Helpful 6
Very old, rotting fences cannot be power washed without ruining the fence. You may have to replace older sections of fence that are badly mildewed or algae covered.

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Helpful 2 Not Helpful 0
Don’t let the pressurized water stream hit plants; even the trunks of large trees could be damaged.

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Helpful 14 Not Helpful 13
Keep children and pets away from the fence while you power wash it.

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