Those dark green or black streaks showing up on the shady side of the house usually mean mildew, not a permanent stain. A bleach solution for vinyl siding — one part household bleach to four parts water — is one of the simplest fixes, but it needs to be mixed and applied carefully.
What You’ll Need
- Plain household chlorine bleach (not “color-safe” or oxygen bleach, which won’t kill mildew)
- Tap water
- 5-gallon bucket
- Pump garden sprayer
- Goggles and rubber gloves
- Garden hose with a spray nozzle
- Long-handled soft brush for stubborn spots
A Ratio That Works
Start with a mild but effective ratio: 1 cup of household bleach to 4 cups of water. Scale it up as needed, but keep the proportion the same. Bathing your siding in stronger bleach can dull the finish over time.
For an area with greasy dirt, a squirt of plain dish soap helps cut through film, but don’t go overboard — too much suds in the sprayer makes rinsing harder.
Applying It the Right Way
- Pick a cloudy, calm day. Bright sun breaks down the bleach too fast, and wind carries spray onto bushes, cars, and walkways.
- Thoroughly wet plants, grass, and flower beds below the work area. Bleach is tough on mildew, and it’s equally tough on greenery.
- Put on your goggles and rubber gloves before mixing or spraying.
- Mix the bleach solution fresh in the bucket, pour it into the sprayer, and apply it to one section at a time.
- Work from bottom to top so the solution doesn’t streak as it runs down. Let it sit for about five minutes, but don’t let it dry on the siding.
- Use the soft brush on any spots that need a little nudge. Stubborn algae stains may need a second light application.
- Rinse thoroughly with the garden hose from top to bottom.
⚠️ Note: Never mix bleach with ammonia, vinegar, or any all-purpose cleaner containing ammonia — the fumes are toxic. When in doubt, use plain dish soap and water, and test a small hidden corner first.
This method won’t repair cracked or badly faded siding, and it isn’t meant for routine dust. But when mildew has taken over, a properly diluted bleach solution is a safe first line of defense. Keep the mix gentle, protect your plants, and rinse well — the bright side of the house will look like it again.
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