How To Clean And Remove Green Algae From A Fence
How we stripped the green algae off our own featheredge fence with a pressure washer and the scrub-by-hand method for anyone without one.
The short answer
To clean green algae off a fence, rinse the loose dirt off, apply a fence or wood detergent if needed, then pressure wash from 2 to 3 feet away on a medium setting with a wide spray pattern, keeping the lance moving in long, even strokes so the soft timber doesn't tear. Without a pressure washer, scrub the boards with diluted bleach or a fence cleaner, leave it for up to 10 minutes and rinse with a hose.
A timber fence looks great when it's clean, but it doesn't stay that way on its own. Dirt, algae and mildew settle into the grain, and in damp, shady spots a fence can turn green surprisingly quickly, especially along the bottom where it's closest to the soil.
That's exactly what happened to the fence in our photos. An overgrown bush had been sitting against it, keeping the boards damp and out of the sun, and by the time we removed the bush the panels behind were coated in green. Cleaning it up took a pressure washer and a little patience, and the difference was obvious straight away.
Pressure Washer Or Bleach For A Green Fence
Both methods work. We prefer a pressure washer, as it's quicker and less effort, and if you don't already own one our pick of the best pressure washers for garden cleaning is a good place to start. Without one, scrubbing diluted bleach or a fence cleaner into the boards by hand is the best alternative, though it takes longer.
Whichever route you take, pick a dry, still day so you can see the results as the fence dries and the spray doesn't drift onto the neighbour's side.
How To Clean A Fence With A Pressure Washer
A pressure washer is the easiest and most effective way to strip green algae off a fence, but the setting matters. Timber is much softer than paving, and a high-powered jet tears up the surface fibres and leaves the boards furry and scarred. Use a medium power setting with a wide spray pattern instead.
Detergent is optional. Fence and wood detergents come as spray-on formulas or as bottles that plug straight into the pressure washer, and they help on heavily soiled panels, though you'll get good results without one. Once the machine is set up, work through the fence in this order:
- Rinse off loose dirt and debris from a distance or on a low setting.
- Apply the detergent by hand or through the machine and spray it across the fence.
- Give the detergent time to work, then rinse it off.
- Stand 2 to 3 feet back with the machine on a medium setting and a wide spray pattern.
- Clean the fence in long, even strokes, following the direction of the boards.
- Keep the lance moving so it never sits on one spot for too long.
The photo above was taken while the fence was still wet, and even then the line between the dirty and clean timber was easy to see. Our short video shows the same fence being pressure washed.
Green Algae On Your Fence? It's A Simple Fix With A Pressure Washer!
Our Fence Before And After Cleaning
Here's the whole run of fence before we started. The worst of the green sits along the bottom of the boards, and you can see a stump left at the edge of the border.
And here's the same fence after 10 to 15 minutes with the pressure washer. There are a few patches that could take another pass, but the boards are back to a pale, natural timber colour and the green has gone from the base.
Cleaning A Fence Without A Pressure Washer
Plenty of people don't own a pressure washer, and some would rather not use one on an older fence in case it damages the panels. Bleach diluted with water, or a dedicated fence cleaner, does the job by hand.
Dip a stiff bristled brush into the solution and scrub it into the boards, working along the grain. Once the dirt is loosened, leave the solution to sit for up to 10 minutes, then rinse the fence clean with a garden hose with a decent spray gun. If any green is still showing once it's dried, repeat the process on those areas. When you're using bleach, protect any plants and lawn at the foot of the fence and rinse them off afterwards, as bleach harms them.
Keeping The Fence From Going Green Again
Algae comes back wherever the timber stays damp and shaded, so cut back shrubs and climbers that sit against the boards and keep soil and leaves away from the base. In our case, removing the bush that caused the problem was half the fix.
Once the fence is clean and dry, you can protect it. Richard, who wrote this guide, prefers the natural look of bare timber, and a fence left unpainted is best given a clean from time to time. If you'd rather add colour and extra protection, our pick of the best fence paints covers paints and stains that go straight onto clean timber, and the same advice applies to decks, as our guide to the best decking paints explains.
The pressure washing technique carries over to hard surfaces too, and our step-by-step guide on cleaning block paving covers driveways. If the fence is past saving and you're starting again, read our comparison of concrete or wooden fence posts before you buy.
Other Questions We Get Asked
Does pressure washing damage a wooden fence?
Pressure washing won't damage a wooden fence on a medium setting with a wide spray pattern from 2 to 3 feet away. Damage happens when the pressure is too high, the nozzle is too close or the jet sits on one spot, which tears up the soft timber and leaves the boards furry. Keep the lance moving in long, even strokes along the boards.
What kills green algae on a fence?
A fence or patio cleaner made for algae and mould kills green algae on a fence, and so does diluted bleach. Scrub it into the boards, leave it to work and rinse it off. A pressure washer removes the algae physically, and running a detergent through it first helps loosen the growth on heavily soiled panels. Removing the shade and damp that caused it stops it coming back.
Should you treat a fence after cleaning it?
Treating a fence after cleaning isn't essential, but it protects the timber and slows the algae returning. Let the fence dry out completely after washing, then apply a fence paint, stain or clear wood preserver. If you prefer the natural look of bare timber, as we do, give it a clean whenever the green starts creeping back.
Why does my fence keep going green?
A fence keeps going green because part of it stays damp and shaded, which is exactly what algae needs to grow. Shrubs and climbers against the boards, soil heaped against the base and a north-facing position all keep the timber wet. Our fence turned green behind an overgrown bush, and removing it was as important as the clean itself.
How long did the fence take to clean with the pressure washer?
The fence in our photos took 10 to 15 minutes with the pressure washer to go from green to pale, natural timber, with a few patches left for another pass. The worst of the green sat along the bottom of the boards. Removing the overgrown bush that kept the panels damp was half the fix.
Is fence detergent worth using with a pressure washer?
A fence or wood detergent is optional. They come as spray-on formulas or as bottles that plug straight into the pressure washer, and they help on heavily soiled panels, though you'll get good results without one. Apply it, give it time to work, then rinse it off before you wash with the machine on a medium setting.
What's the best weather for cleaning a fence?
Pick a dry, still day. You can see the results as the fence dries, and the spray doesn't drift onto the neighbour's side. If you're using bleach by hand, protect any plants and lawn at the foot of the fence and rinse them off afterwards, as bleach harms them.
Would you use bleach rather than a pressure washer on an older fence?
We prefer a pressure washer because it's quicker and less effort. Anyone who'd rather not use one on an older fence in case it damages the panels can scrub diluted bleach or a fence cleaner into the boards by hand. It takes longer, and you leave the solution to sit for up to 10 minutes before rinsing.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.