Removing Algae, Mold and Mildew Off Wood Fences

You probably remember when your wood fence looked clean, solid, and maybe even a little charming. Now it’s got that dark, blotchy, greenish-black coating that no amount of garden hose rinsing seems to touch. You’re not imagining it getting worse, it genuinely is. Algae, mold, and mildew spread across wood surfaces at a surprisingly aggressive pace, especially in humid or shaded areas. At Sunny Pressure Washing, we’ve helped hundreds of homeowners reclaim their fences from exactly this kind of biological buildup, and we want to help you understand what’s actually going on and what it takes to fix it the right way.

The reality is that wood fences are essentially a perfect habitat for algae, mold, and mildew. Wood is porous, which means it absorbs moisture easily and holds onto it and wherever moisture lingers, organic growth follows. According to the EPA, mold can begin developing on a damp surface in as little as 24 to 48 hours. Multiply that across weeks of rain, morning dew, and limited sunlight, and you’ve got a recipe for the green and black mess that’s quietly eating away at your fence right now.

What most homeowners don’t realize is that this isn’t just a cosmetic issue. Left untreated, algae, mold, and mildew break down the wood fibers themselves, leading to softening, cracking, and eventual rot. What might cost a few hundred dollars to clean today could easily turn into thousands in fence replacement costs if ignored long enough.

What Pressure Washing Actually Does to Organic Growth

Pressure washing works by delivering a high-velocity stream of water that physically dislodges and flushes away surface contaminants. For algae, mold, and mildew on wood fences, that means breaking up the root-like structures (called hyphae in the case of mold) that anchor the growth to the wood grain. When done correctly, pressure washing doesn’t just clean the surface — it removes the biological material that would otherwise keep spreading.

Choosing the Right Pressure and Technique for Wood

This is where a lot of DIY attempts go sideways. Wood fences require a much gentler approach than concrete driveways or brick walls. Too much pressure — anything above roughly 1,500 PSI without proper technique — can gouge the wood, raise the grain, and actually make the surface more vulnerable to future mold and mildew growth by creating more microscopic grooves for moisture to hide in.

Professional pressure washing services use what’s known as a “soft wash” approach for wood surfaces. This combines lower pressure with a specialized cleaning solution — typically one that’s sodium hypochlorite-based — that kills the mold and algae at the root rather than just blasting the visible layer away. The result is a deeper, longer-lasting clean that actually gives your fence a fighting chance.

Pre-Treatment and Post-Treatment Matter Just as Much

Getting the pressure washing itself right is only part of the equation. Pre-treating the fence with a mold-killing solution and allowing proper dwell time — usually 10 to 15 minutes — lets the chemistry do the heavy lifting before the water even touches the surface. After the wash, applying a wood sealant or UV-protective stain dramatically extends the results by closing off those porous wood fibers and cutting off the moisture access that mold and algae depend on.

How Long Will the Results Last?

With a proper professional cleaning and a post-treatment sealant, most wood fences stay noticeably clean for anywhere from one to three years, depending on the amount of shade, rainfall, and nearby vegetation. Fences under heavy tree coverage will need more frequent attention simply because they stay damper longer.

Don’t Let Green Turn Into Gone

Your fence is both a functional boundary and a first impression of your home. Algae, mold, and mildew don’t just make it look neglected; they’re actively shortening its lifespan with every passing season. The good news is that a professional pressure washing service can reverse months or even years of biological buildup in a single afternoon.

If your fence has started showing those tell-tale dark patches and greenish streaks, now is the right time to act, before the damage goes deeper than the surface. Reach out to Sunny Pressure Washing today for a free estimate, and let’s get your fence looking the way it’s supposed to.