How do I remove moss and algae from my Ottawa patio?

Moss and algae thrive on Ottawa patios because our climate gives them exactly what they need — long periods of moisture from spring snowmelt, summer humidity, and fall rains, combined with shaded areas where surfaces stay damp for days at a time. North-facing patios and those shaded by mature trees are particularly prone, and you will often see the first green patches appear in April as snow recedes and temperatures hover near freezing.

Before reaching for chemicals, start with mechanical removal. A stiff-bristled push broom or a dedicated patio scrub brush will dislodge most surface moss and algae from concrete pavers, natural stone, and stamped concrete. For textured surfaces where growth has taken hold in crevices, a pressure washer set between 1,500 and 2,000 PSI works well. Keep the nozzle at least 12 inches from the surface and use a fan tip rather than a zero-degree tip to avoid etching pavers or dislodging joint sand.

For stubborn growth, a cleaning solution of one part white vinegar to one part water is effective and safe for most patio materials. Apply it generously, let it sit for 15 to 20 minutes, then scrub and rinse. Oxygen bleach (sodium percarbonate) is another excellent option — it kills moss and algae without harming nearby garden plants the way chlorine bleach can. Mix it according to the package directions, apply with a pump sprayer, wait 10 to 15 minutes, and scrub with a brush before rinsing thoroughly.

Avoid chlorine bleach on coloured concrete pavers or natural stone, as it can cause discolouration and degrade the surface over time. It can also kill surrounding grass and garden plants if runoff reaches your beds — a real concern on Ottawa properties where patios often sit adjacent to perennial gardens.

Once the patio is clean, address the conditions that encourage regrowth. Trim overhanging branches to increase sunlight and airflow across the surface. Ensure that downspouts and grading direct water away from the patio rather than pooling on it. Check that your paver joints are properly filled with polymeric sand, as empty or eroded joints trap moisture and give moss a foothold.

Applying a paver sealer after cleaning creates a protective barrier that makes future moss and algae removal much easier. Sealers also help protect against the salt and sand damage that Ottawa patios endure each winter. The best time to seal is late spring or early fall when temperatures are consistently above 10°C and rain is not expected for 24 hours — typically late May or September in Ottawa.

For patios with persistent moss problems that return every spring despite cleaning, the underlying issue may be poor drainage or insufficient base slope. An Ottawa patio specialist listed in our contractor directory can assess whether regrading or drainage improvements would solve the problem permanently.

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Looking for experienced contractors? The Ottawa Construction Network connects Ottawa homeowners with qualified professionals:

• Justyn Rook Contracting
• RenoMotion Inc.
• Ottawa Caulking
• The Granite shop
• Floor-2-Wall Inc