Prep first
Before you start
- Sweep off loose pollen and debris while the deck is still dry.
- Rinse with a garden hose on a low-pressure spray before you apply anything.
- Don't use steel wool or wire brushes on the wood.
Algae and moss on a deck show up as dark streaks and slick patches, and they return fastest on boards that stay damp. Wood can take water and an oxygen cleaner, but abrasives need care, so the scrub has to stay gentle. If the boards have weathered gray or old stain is still on them, the job changes and may need a restorer and light sanding.
To clean pollen off a deck without stripping the stain, keep the scrub gentle and let an oxygen cleaner do most of the work. Pollen on a stained deck and algae on decking need the same careful touch, so don't push harder if the first pass doesn't lift it. If the boards still look gray after a full round, that's the point to think about a restorer.
Before you start
What decks & wood fences can take
Safe to use2
- Water
- Oxygen bleach
Use with care5
- Soaking
- Chlorine bleach
- Solvents (alcohol, spot removers)
- Acids (vinegar, lemon)
- Scrubbing and abrasives
7 items
What you'll need
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- Broom or stiff brushclears loose pollen and debris while the deck is dry (opens Amazon)
- Garden hose with a spray nozzlegives the low-pressure rinse the wood needs
- Oxygen bleach (sodium percarbonate) or commercial deck cleanerlifts the growth from the wood (opens Amazon)
- Stiff synthetic-bristle brushscrubs along the grain without roughing up the boards (opens Amazon)
- Bucketholds the cleaner while you mix and apply it (opens Amazon)
- Old clothes, shoes and rubber glovesprotect you from the cleaner
- Cellulose sponge (opens Amazon)
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6 steps
Step by step
Step 1 of 6
Sweep off the loose debris
Brush off loose pollen, leaves and grit while the deck is still dry. Work along the grain so the debris lifts off the boards instead of getting pushed into the gaps between them.
Step 2 of 6
Rinse the boards on low pressure
Wet the whole deck with a garden hose on a low-pressure spray. Wet wood lets the cleaner spread evenly when it goes on.
Careful. Don't use narrow-stream or rotating 'tornado' pressure-washer tips on decks.
Step 3 of 615 minutes
Apply the oxygen cleaner
Apply oxygen bleach (sodium percarbonate) or a commercial deck cleaner with a brush or sponge, covering the whole surface of each board. Let it stay wet on the wood for about 15 minutes, misting with the hose whenever it starts to dry.
Careful. Don't let cleaners or soap dry on the deck.
Step 4 of 6
Scrub along the grain
Scrub each board with a stiff synthetic-bristle brush, moving with the grain. Heavy growth in shaded spots may need a second pass before you rinse.
Careful. Don't use steel wool or wire brushes on wood, since leftover iron reacts with the wood and stains it.
Step 5 of 6
Rinse the deck thoroughly
Rinse the whole deck with the garden hose until no cleaner or loosened growth is left on the boards. Start at the far end and work toward the steps so the runoff carries everything off.
Tip. Rinse the railings and stairs too, since the runoff passes over them.
Step 6 of 6
Let the deck air dry
Leave the boards to air dry fully in the open. Once they're dry, check for any dark patches that remain, since those need the heavier treatment covered below.
If you'd rather buy than mix
Best products for algae on decks & wood fences
Look for an oxygen bleach or a commercial deck cleaner that is labeled for wood decks. Check that it's made for decks before you buy.
OxiClean Versatile Stain Remover Powder
How we picked these: each product is made for this type of stain, its maker doesn't warn against using it on decks & wood fences, and its directions fit the steps above.
Finished the steps? How does it look?
Nice work. Let it dry completely and check it again in good light. Here is what done looks like:
How to tell it's really gone →A faint mark usually needs one more round, not a stronger product.
Heavy buildup usually takes more than one round.
Heavy or long-standing buildup →When to call a professional →How to tell it's working
The deck is clean when the boards look even in color and the green or black growth is gone from the grain. Water should run off without leaving dark wet patches. If streaks come back once the wood is dry, the growth is still there, and the set-in section below is the next move.
What changes for yours
Adjust for your decks & wood fences
Stained Deck with Pollen
Pollen on a stained deck starts the same way: sweep off the dry pollen before anything touches it with water. Skip the hose at this stage, because wet pollen turns into a film that's harder to brush away.
Once the loose pollen is gone, rinse, clean and scrub only if growth is still there. Test the cleaner on a small hidden board first, since you can't know how your stain will react.
Shaded Boards
Moss grows where boards stay damp, so shaded boards and the ones under trees usually need the scrub twice. Give them the second pass during the scrub before rinsing.
Shaded boards also take longer to dry, so wait until they're fully dry before you judge the results. Keep the rinse on the same low-pressure spray as the rest of the deck.
Railings and Stairs
Railings, balusters and stair treads have more edges and gaps where growth collects. Scrub the edges and gaps with the same brush, working along the grain of each piece.
Rinse these from the top down so the runoff carries the loosened growth off the lower parts. Check the gaps once they've dried, since growth can hide in them.
Light Growth
A light film with no thick growth usually comes off in one pass. Skip the second scrub and rinse once the cleaner has stayed wet for about 15 minutes.
If the film is still visible after the wood dries, the growth has set in, and the set-in section covers what to do next. Keep the same low-pressure rinse so the wood isn't roughened.
Heavy or long-standing buildup
Old growth that has been on the deck for years may not come off in one pass. Give those spots about 15 minutes of wet dwell again, and scrub them with the same stiff synthetic brush before rinsing.
If dark patches are still there after the wood has dried, repeat the cleaning on just those spots rather than the whole deck. Working only the spots that need it keeps the rest of the boards from being worked over again.
For weathered, grayed boards, a commercial deck cleaner, brightener or restorer is the next step up, and it removes mildew and dirt so the wood's own color can show. If all the natural color has leached out, the wood stays silver when dry, and those fibers should be left in place rather than scrubbed away. Expect partial results on very old boards, since no cleaner brings back color that's already gone.
Vinegar, baking soda, peroxide and more
Do home remedies work on algae on decks & wood fences?
You can clean algae off a deck without removing the stain: the sweep, rinse, cleaner and scrub in the steps lift the growth and leave the finish alone. Most household remedies are built for fabric, fresh spills or countertops, so they don't belong in this routine. Here is how each common remedy holds up for a deck.
Works1Skip5
What makes it worse
Mistakes to avoid
Don't use chlorine bleach on a pressure-treated deck.
Bleach breaks down the lignin in the wood, corrodes metal fasteners and harms nearby plants, and it doesn't kill the mildew spores. The oxygen cleaner in the steps does the job without those costs.
Don't wet-clean an old CCA deck with kids and pets around.
Wetting old CCA-treated wood raises the arsenic at the surface, and bleach releases chromate, so keep children and pets off the wet boards. If the deck is old CCA lumber, replacing it is safer than cutting or burning it, since the sawdust and smoke contain arsenic.
Don't scrub with caustic cleaners or power wash soft wood.
Harsh cleaners and heavy pressure on soft woods such as western redcedar strip away the wood surface. Stick to the gentle scrub and hose rinse in the steps.
When to call a professional
Call a pro if the wood feels soft or splintery, or if the growth returns right away after repeated cleaning. Pressure washing in the wrong hands can damage a deck, so leave that tool to someone experienced.
Questions
How do I get pollen off a deck without making it worse?
Sweep it off dry first, since wet pollen is harder to clear. Then rinse with a garden hose on a low-pressure spray, and the cleaning steps handle anything left.
Will the cleaner strip my deck's stain?
No. The steps clean the growth off the boards without calling for a stain and sealer remover, so the finish is left alone. Stripping old stain or sealer is a separate job that calls for its own remover.
How long should the cleaner stay on the wood?
About 15 minutes, with the wood kept wet the whole time. If the boards start to dry out, mist them with the hose.
What if dark streaks are still there after cleaning?
Wait until the wood is fully dry, then check the spots. Repeat the cleaning on just those spots, and if the wood has grayed all the way, a commercial deck brightener or restorer is the next step.
Can I walk on the deck right after cleaning?
Wait until the boards have air dried fully. Wet wood can be slippery, so keep off the deck until it's dry.
Can I use dish soap to clean a deck?
It isn't the right choice. Dish soap is meant for fabric spots, and a commercial deck cleaner is made for wood, so use that or the oxygen cleaner instead.
Algae on other materials
Other stains on decks & wood fences
Start from the bigger picture
How we know this
Every method, amount and warning here comes from university extension services, industry bodies and product makers. We read them, check every step for unsafe combinations and changed amounts, and write it up so you can follow it.