How to remove algae from decking safely

Algae turns decking from a lovely garden feature into a green, slimy slip hazard almost overnight — especially in the damp corners of a Lincolnshire garden. The good news is that knowing how to remove algae from decking safely means you can get it looking clean and solid again without splintering the boards or leaving them worse than before.

The short answer: a careful clean with the right product and the right technique removes algae completely. The wrong approach — blasting it with a pressure washer at full power, for example — can strip the grain and leave the wood furry and rough. Here's exactly what to do.

Why decking gets so green in the first place

Algae, like moss and lichen, loves moisture and shade. Decking is particularly vulnerable because wood is porous — it soaks up rainwater and holds onto it, giving algae spores everything they need to settle and spread. Gardens in wetter parts of Lincolnshire, such as the low-lying areas around Saxilby or Washingborough, can see green growth appear within a season if the decking doesn't dry out quickly between showers.

A north-facing deck, one shaded by a fence or a large tree, or one that stays damp under pot plants will green up fastest. Understanding that helps you prevent the next outbreak once the boards are clean.

What you'll need before you start

Gather everything before you begin so you're not stopping halfway through:

• A stiff-bristled brush or a specialised decking brush (long-handled to save your back)
• A garden hose or low-pressure washer
• A deck cleaner or algae remover suitable for wood — look for an oxygenated or sodium percarbonate-based product rather than bleach, which can discolour and dry out timber
• Protective gloves and old clothes
• A pump sprayer if you're treating a large area

Avoid household bleach. It kills algae on contact but strips the natural oils from timber and can leave grey tide marks that are hard to shift.

How to remove algae from decking step by step

1. Clear the deck. Move furniture, plant pots and anything else off the boards so you have full access.
2. Rinse the surface. Wet the boards with a hose first. This lifts loose dirt and stops the cleaner soaking in unevenly on bone-dry wood.
3. Apply your deck cleaner. Mix according to the instructions and apply generously using a brush or pump sprayer. Work along the grain of the wood, not across it.
4. Allow it to dwell. Most wood-safe algae removers need 10–20 minutes to work. Don't let the product dry on the surface — if it starts to, add a little more water.
5. Scrub along the grain. Use your stiff brush in firm, steady strokes along the length of each board. You'll see the green lifting as you go.
6. Rinse thoroughly. A garden hose at decent pressure is usually enough. If you're using a pressure washer, keep it on a fan setting, hold the lance at least 30 cm from the surface, and always work along the grain.
7. Let it dry completely. Don't replace furniture for at least 24 hours, longer if the weather is overcast.

Should you pressure wash decking?

A pressure washer can be a useful tool on decking — but only used carefully. The risk is that a narrow jet at close range will raise the grain of the wood, leaving a fibrous, rough surface that actually traps more dirt and moisture in future. That accelerates the problem rather than solving it.

If you do use one, stick to a wide fan nozzle (40-degree tip or wider), keep it moving, and never hold the lance still. On older, softer timber — treated pine decking that's seen a few Lincolnshire winters — a soft wash with chemical treatment and a brush is almost always safer than a pressure washer alone.

For peace of mind, our decking and wood cleaning guides cover the full range of timber surfaces and what each one needs.

Treating the wood after cleaning

Once the decking is fully dry — which can take a day or two after a proper clean — it's worth applying a decking oil or UV-protective wood stain. This does two things: it feeds the timber and helps it resist moisture, and it reduces the rough, open-grained surface that algae loves to colonise.

You don't need an expensive product. A good-quality decking oil applied in the direction of the grain once a year keeps timber in far better condition than leaving it untreated and cleaning it harder each time.

Stopping algae coming back

Cleaning is only half the battle. A few simple habits will reduce how quickly the green returns:

• Move pot plants and furniture occasionally so air and light can reach every part of the surface
• Trim back overhanging plants or fencing to let more sunlight hit the deck through the day
• Apply an annual treatment — a light clean and re-oil each spring keeps on top of it before algae gets established
• Don't let leaves sit on the boards through autumn and winter; wet, decaying leaves are a perfect algae starter

Many customers in places like Nettleham and Branston find that one thorough professional clean followed by a proper oil gives them two to three seasons before they need to do it again.

When to call in a professional

If the algae has been left for several seasons and is thick, or if the boards have started to grey and dry out significantly, a DIY clean might not get on top of it fully. A professional soft wash uses the right dilution of treatment products for the specific timber, removes algae right down to the root, and can assess whether any boards have deteriorated beyond cleaning.

We work across Lincolnshire — from Lincoln and Waddington down to the villages further out — and we carry the right equipment to clean decking without causing damage. Take a look at our full range of outdoor surface services or browse the areas we cover to see if we're nearby.

If you'd like us to restore your decking this season, get a free quote today. We'll give you an honest assessment and a clear price — no obligation.

Frequently asked questions

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Need a hand with yours? We cover Lincolnshire for patios, driveways, paths and more — see the areas we cover or browse our services. Get a free quote or call 07874 010739.