Cleaning Moss Off Decking, Paving and Garden Furniture

Brush it, wash it if the surface allows, and fix what keeps it damp. Moss and algae on decking, paving and furniture do not damage what is underneath but make surfaces slippery, and they come back wherever damp, shade and debris persist, so one clean rarely holds in a Scottish garden. Non-chemical methods are effective, and there is no need for mosskillers or chemical patio cleaners.

This covers hard surfaces: decking, paving and patio stone, garden furniture and fences. For moss in grass, see moss in your lawn, which covers scarifying and lawn treatment.

Why it keeps coming back

Algae thrive in wet conditions, and growth is faster in shady areas with poor air circulation, with build-ups often after wet winters. On hard surfaces it needs something to hold onto: a rough or porous texture such as weathered wood grain, mortar joints or textured stone, plus a film of organic debris. Cooler temperatures and a lower sun mean wet surfaces in much of Scotland take longer to dry between showers, especially anywhere shaded or north-facing, so treat this as maintenance on a cycle, a proper clean once or twice a year with small habits in between, not a one-off job.

What works, by method

Brushing on a regular basis helps stop growth taking hold, and it is the safest first method. Use a stiff, non-wire broom on timber: a wire brush suits hard masonry but can gouge and fuzz softwood fibres. Work moss out of paving joints with a pointed tool or old knife; repointing loose joints and filling gaps limits the spaces where it settles.

Pressure washing lifts established growth quickly, with care. Use the widest fan setting, hold the nozzle further back than feels necessary, and test a hidden corner first, because the aim is to lift the moss layer, not blast into the wood or stone. Where drainage is poor the extra water can worsen damp problems, and it does not stop regrowth. Wear goggles.

Timing matters. Choose a dry spell, not straight after rain when everything is saturated, and avoid frozen or icy surfaces, since wet moss on a cold surface is slippery before you start.

Cleaners, vinegar and bleach

If you want a chemical cleaner, benzalkonium chloride patio cleaners are one option, and most proprietary patio cleaners remove algae, lichens and liverworts. Most are non-persistent, so repeat applications are needed, and growth returns if conditions are unchanged. Follow the label on dilution, the surface it is intended for (a decking-safe product is not always the same as a patio cleaner) and runoff near beds, and wear gloves.

Diluted white vinegar is often suggested and is acidic enough to kill exposed growth, but the RHS advises against applying household products such as vinegar and bleach to soil, because they damage plants, soil and soil organisms. Rinsing it off a patio sends it into the borders around it, so if you use it, keep it to small areas that drain away from planting, and avoid it on limestone, sandstone and lime mortar, which acid can etch. Test an unobtrusive patch first.

Bleach is best left out. On hard surfaces, cleaners based on bleach or hydrochloric acid have some effect but are not recommended near plants and can discolour certain stone. Bleach may also weaken and grey timber, and runoff harms soil and roots. Do not let any cleaning product wash straight into a drain or watercourse.

Surface by surface

Decking. Treated softwood tolerates a moderate pressure wash if you keep the nozzle moving, though the grain still raises with repeated high-pressure cleaning. Older, untreated or weathered softwood is more vulnerable to splintering, so favour brushing. Reapplying decking oil or sealant afterwards protects the wood and may slow how quickly moss re-establishes. Composite (wood-plastic) decking does not need oiling and generally tolerates more pressure, but check the maker's guidance on nozzle type first.

Paving and patio stone. Natural stone and concrete flags tolerate pressure washing, but keep the jet away from the joints, which blows out the sand or mortar and leaves gaps for weeds. Work joints separately with a tool.

Garden furniture. Treat wood like decking. Rattan and wicker do not suit pressure washing, as water forcedCovering plants to exclude light and speed early, tender growth in the dark, most associated with rhubarb and sea kale in late winter. Full definition → into the weave is slow to dry and may encourage growth; brush, then dry fully. Plastic and resin are the most forgiving. On metal, check for rust starting under old moss patches, since trapped damp against bare or chipped metal does the long-term damage, not the moss.

Fences. Treat them like decking of the same wood type: brushing for older timber, a careful low-pressure wash for younger treated panels, and periodic re-staining on the shaded side.

Keeping it from coming back

Prevention means breaking one of the three things growth needs: damp, shade or debris.

• Improve drainage. Surfaces should slope slightly so water runs off, and a shallow gravel-filled channel along the edge carries it away. Lightly forking over beds close to hard surfaces helps drainage and water absorption, and clear drains of leaves.
• Reduce shade where practical. Pruning overhanging branches and shrubs lets sun and wind dry the surface; it need not be drastic.
• Clear debris regularly. Sweep leaves and organic litter off through autumn and winter, and keep gutters and drains clear.
• Re-treat on a schedule. Oiled decking and stained fences need reapplication, typically annually.

Kept up over a couple of seasons this stretches the gap between cleans and keeps each one lighter. Away from surfaces that are walked on, algae, lichens and liverworts often need no removal at all.

Common questions

Sources