Vinyl & Brick House Siding
Why Are Black Streaks and Green Mildew on My Shady Siding? And How Does Soft Washing Help?
A simple guide to understanding and safely removing organic growth from vinyl and brick.
October 4, 2026
Have you ever looked at the shady side of your house and seen ugly black streaks or green fuzzy patches? You might ask: Why are these things growing there, and how can I get rid of them without damaging my siding? You're not alone. Many homeowners wonder the same thing. The good news is that the answer is simple, and the safe solution is called soft washing.
What Are Those Black Streaks and Green Spots?
The black streaks are usually a type of algae. It's a living plant-like organism that floats through the air and lands on your siding. It loves moisture and eats tiny bits of dust and dirt. The green stuff is often mildew or moss. Mildew is a kind of fungus, and moss is a small plant. Both grow in damp, shady places.
Why Do They Love the Shady Side of Your Home?
The shady side of your house stays wet longer. When the sun doesn't hit it, water from rain or dew doesn't dry up quickly. Algae, mildew, and moss need water to grow. They also don't like strong sunlight, which can dry them out and kill them. So the shady side becomes a perfect home for them. That's why you see more growth there than on the sunny side.
Can't I Just Power Wash Them Away?
Power washing (also called pressure washing) uses very strong water pressure. It might blast off the black streaks, but it can also cause big problems. On vinyl siding, high pressure can force water behind the panels, which can lead to rot or mold inside your walls. It can also crack or chip the vinyl. On brick, high pressure can damage the mortar between the bricks and even break the bricks themselves. Plus, power washing often just removes the top layer of growth. The roots or spores stay behind, so the streaks come back quickly.
How Does Soft Washing Work?
Soft washing is a much gentler method. It uses low water pressure—about the same as a garden hose—along with special cleaning solutions. These solutions are made to kill algae, mildew, and moss at their source. The cleaner is sprayed onto the siding, and it soaks in for a few minutes. Then it's rinsed away with low pressure. Because the solution kills the organisms, they don't just grow back right away. Soft washing is safe for vinyl siding, brick, and many other surfaces. It cleans deep without causing damage. It also reaches into cracks and crevices where power washing might miss.
Practical Tips to Slow Down Growth
You can do a few things to keep the shady side cleaner for longer:
- Trim bushes and tree branches so more sunlight reaches the wall and air can flow.
- Keep gutters clean so water doesn't overflow and run down the siding.
- Fix any leaky hoses or sprinklers that keep the wall wet.
- Make sure downspouts direct water away from your foundation.
- Consider a professional soft wash every year or two to stay ahead of the growth.
How Skinner Cleaning LLC Can Help
If you see black streaks or green mildew on your home, don't reach for a pressure washer. Call Skinner Cleaning LLC. We specialize in soft washing for vinyl and brick siding. We can answer your questions and safely remove the ugly growth without damaging your home. Our team will clean your siding effectively. Contact Skinner Cleaning LLC today to schedule your soft washing service. Let us help you keep your home beautiful and protected.
Need Help With Why Are Black Streaks and Green Mildew on My Shady Siding? And How Does Soft Washing Help??
Skinner Cleaning LLC can help. Contact our team today to talk through your needs and schedule service.