Green mold and algae on a wood fence are living growth, not dirt. Kill them with a surface-safe cleaner, rinse at low pressure, and fix the shade and moisture that let them take hold. Blasting them with high pressure alone spreads the growth and damages the wood.
Why the shaded side greens first
Algae and mildew need moisture and low light to establish. The north side of a fence gets the least direct sun, so it stays damp longer after rain and dew. Fences under overhanging trees or beside dense shrubs green up for the same reason. In Central Texas, where we get heavy rain followed by humidity, shaded fence lines can turn green within a single season. The growth starts as a thin green film and thickens into a slimy layer that traps more moisture against the wood.
What actually removes it
- Apply an oxygen bleach cleaner (sodium percarbonate) mixed with warm water, using a pump sprayer. Let it dwell for 10 to 15 minutes. This kills the growth at the root rather than just bleaching the surface.
- Rinse at low pressure with a wide fan tip, working with the grain from top to bottom. Keep the nozzle at a consistent distance and never use a narrow tip.
- Follow with an oxalic acid wood brightener if the wood is still gray. The brightener neutralizes the alkaline cleaner and restores the natural wood color.
- Let the fence dry completely for at least two days before any stain or sealer goes on.
Why high pressure makes it worse
A pressure washer set too high or held too close tears out the soft wood fibers between the grain lines, leaving a fuzzy, ridged texture. That fuzz traps dirt faster than before and drinks stain unevenly. High pressure also spreads algae spores to clean sections of the fence, so the problem comes back quicker and wider. The cleaner does the killing. The water only has to rinse.
The right cleaner for the job
- Oxygen bleach (sodium percarbonate) is the default choice. It kills algae and mildew, lifts gray weathering, and breaks down to oxygen, water, and soda ash without harming plants when used as directed.
- Oxalic acid brightener follows cleaning to restore wood color and remove iron streaks. It does not kill algae on its own.
- Chlorine bleach is not recommended as a routine fence cleaner. The EPA advises against using biocides like chlorine bleach for mold cleanup as a routine practice, and bleach can damage wood fibers and harm nearby plants.
- Dish soap and water remove light dirt and pollen but will not kill established algae or mildew.
Preventing it from coming back
- Trim back overhanging branches and thin dense shrubs so sun and air reach the fence line.
- Adjust sprinklers so they do not soak the same section of fence daily.
- Keep soil, mulch, and vegetation from resting against the bottom boards.
- Stain or seal the wood with a product that contains mildewcide. A penetrating stain with zinc nanoparticles resists mold and mildew growth.
- Clean the fence on a schedule before heavy buildup returns, typically every one to two years in shaded Central Texas yards.
If the fence is heavily rotted or the boards are falling loose, cleaning will not fix it. Repair or replace the damaged sections first, then clean and stain the sound wood. If you would rather not tackle it yourself, we can assess the fence and handle the cleaning and staining for you. A professional assessment also catches problems that are easy to miss from the ground, like loose fasteners, posts that are starting to rot at the base, or sections where the wood has started to delaminate.
Common questions
Can I use bleach to clean green mold off a wood fence?
Will a pressure washer alone remove algae from a fence?
How do I keep algae from coming back on my fence?
Related: Fence & deck staining service, How to prep a fence before staining, How often to stain a fence in Central Texas
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