When you first install siding on your home, it’s like a fresh haircut—clean and sharp. It makes everything look put together. But just like a neglected mop of hair, your siding can go from sleek to streaked if you’re not careful.
Those green and black streaks? That’s algae and mildew taking over your siding, and if you let them settle in, they’ll do more than tarnish your home’s look—they’ll compromise the very health of your siding.
The good news is that you don’t have to let your home become a science experiment in unwanted growth. With some maintenance with the help of “exterior siding contractors near me” or these DIY tips, you can keep your siding looking fresh and fungus-free.
Why Algae and Mildew Grow on Siding
Algae and mildew aren’t just eye sores—they’re the squatters of the siding world, moving in uninvited and refusing to leave.
Algae, typically green and streaky, form in humid, shaded areas with little sunlight. Mildew, which looks more powdery and gray or white, is a fungus that thrives in similar conditions. If moisture is present for long enough, these nuisances can cling to vinyl, wood, fiber cement, or metal siding.
If you’ve ever noticed green streaks on the side of your house that doesn’t get much sun, you’ve seen how this issue plays out. Rain, irrigation runoff, and even dew can linger on your siding; if there is limited airflow, that water has nowhere to go. Add falling leaves or pollen, and you’re building a buffet for mold and algae to feast on.
Ignoring algae and mildew is like giving them the “go-ahead” to take over your home’s exterior. The longer you wait, the harder they become to remove, and eventually, the damage might require more than just cleaning—it could mean a complete replacement.
Clean Routinely
A little cleanup is your first line of defense to keep the siding healthy. Think of regular cleaning like brushing your teeth—skip it too long, and things start growing where they shouldn’t. Don’t wait until you see green streaks or black patches before you act. Wash your siding at least once a year, but if your area is humid or wooded, do it more frequently.
Use a soft or long-handled siding brush, a mild cleaning solution, or a specially formulated siding cleaner. A simple mix of water and vinegar or water with a small amount of dish soap can also be effective. Start from the bottom and work your way up, rinsing thoroughly as you go to avoid streaking. If you notice stubborn spots, add some oxygen bleach to your cleaning solution to help clean without the harshness of chlorine bleach.
Avoid power washers unless you’re confident in your technique. Too much pressure can damage the siding or force water behind it, worsening moisture issues. Gentle and thorough wins the race here, not brute force.
Control Moisture Around Your Home
You can’t always control the weather, but you can control how moisture interacts with your home. One of the most impactful steps you can take is to make sure your gutters and downspouts are clean and functioning correctly. If rainwater overflows or pools around your foundation, you’re essentially inviting mold and algae to grow.
Also, check that your sprinklers aren’t hitting your siding every time they run. Repeated soaking may not seem like a big deal initially, but it creates a damp environment ideal for growth. Redirect sprinkler spray to stop unnecessary moisture buildup.
If you have landscaping around your home, make sure it isn’t trapping moisture against the walls. Trim bushes and trees so air can circulate freely around your siding, allowing it to dry quickly after rain or irrigation. Algae and mildew love a damp, cozy home—don’t be the generous host they’re hoping for.
Bring In Sunlight and Ventilation
Sunlight is nature’s disinfectant—give your siding a little sunshine, and algae and mildew won’t stand a chance. You may not be able to move your house or remove large shade trees, but you can make thoughtful decisions about your landscaping to let in more light where it’s most needed.
Airflow also plays a crucial role. Areas that trap humidity—like tight corners or behind tall shrubs—tend to stay damp. You might not realize it, but poor ventilation can harm siding, too. Look for areas on your home’s exterior with restricted airflow. Reposition a fence panel or thin out dense hedges to reduce drying times.
Fresh air and sunshine aren’t just good for you. They make your home a terrible vacation spot for mold and mildew—exactly how you want it.
Use Preventative Treatments and Coatings
Once your siding is clean and dry, you can go further by applying protective treatments that help resist algae and mildew growth. A good protective coating is like sunscreen for your siding, shielding it from the elements and keeping the grime at bay.
Certain siding materials—like fiber cement or treated wood—may already have coatings that resist mold and mildew. But even vinyl siding can benefit from an after-cleaning treatment designed to slow the return of organic growth.
These products are often applied using a garden sprayer and can last anywhere from six months to a few years, depending on your local environment. Choose a product compatible with your siding type and won’t degrade its finish. Some include a fungicide or algaecide, while others create a water-resistant barrier that reduces moisture retention.
Always read labels and follow manufacturer recommendations. A little time spent on the application can save you hours of scrubbing in the future.
Call In the Professionals
While DIY maintenance works well in most cases, some battles are best left to the experts. Maintaining your siding isn’t just about cleanliness. Algae and mildew might start as cosmetic issues, but over time, they can lead to siding deterioration, hidden leaks, and even health concerns if mold spreads into your home.
If there is extensive mold on your siding, you may not be equipped to remove it safely—especially if the spores have spread to hard-to-reach areas. Professionals can use commercial-grade cleaning agents and equipment to thoroughly clean the surface without damaging your siding.
If you have recurring growth despite your best efforts, it may point to a deeper issue, such as poor insulation, damaged vapor barriers, or even internal moisture problems. A home siding installation specialist can assess your home’s condition and recommend permanent solutions.
Sometimes, the best tool for the job is a phone call—let the professionals tackle the mess so you don’t have to. Otherwise, with just a little time and effort, you can refresh that clean look that made you love your home in the first place. Don’t underestimate the power of regular maintenance—your siding will thank you, season after season.