Green or Black Streaks on Your Siding? Here's What's Growing There
If your siding has developed green or black streaking, it's tempting to assume it's just dirt that washed down unevenly. It's usually not — and knowing the difference changes how you should clean it.
What's actually causing the streaks
Green streaking is typically algae — most commonly a type called Gloeocapsa magma, which thrives in damp, shaded areas of your home's exterior. It grows on the surface and can spread across siding, especially on north-facing walls that get less direct sun.
Black streaking is usually mold or mildew, often appearing in the same shaded, moisture-prone spots. Unlike surface dirt, both algae and mold can root into slightly porous surfaces, which is why a quick rinse rarely removes them fully.
Why pressure alone doesn't fix it
Since algae and mold are growing into the surface rather than just sitting on top, blasting them with plain water pressure often only removes the visible top layer — the roots stay behind, and the streaking comes back within weeks or months. It's also risky: high pressure on vinyl siding can crack panels or force water behind them.
What actually works
Soft washing uses a specialized cleaning solution designed to kill algae, mold, and mildew at the root, combined with low pressure to safely rinse it away without damaging the siding underneath. This is the difference between a clean that lasts and one that's back by the next rainy season.
Is it hurting your siding?
Left untreated long enough, algae and mold growth can contribute to surface staining that's harder to remove over time, and in some cases can affect siding materials directly. Beyond appearance, it's also just a sign of ongoing moisture exposure in that area — worth knowing about for your home's overall maintenance.
How to prevent it from coming back
Trim back trees or shrubs shading the affected area, where possible — more sunlight means less algae growth
Keep gutters clear so water isn't running down the siding
A once or twice a year professional wash keeps growth from re-establishing long-term
Ready to get rid of it for good?
Get a FREE quote and we'll soft wash your siding the right way — solution that actually kills the growth, not just a rinse that hides it for a few weeks.
