Green Algae on Siding: What It Is and Why Baton Rouge Homes Get It
Quick answer
The green film on your siding is algae and mildew. It grows where siding stays damp and shaded, and Baton Rouge's heavy rain gives it plenty of both. A low-pressure soft wash kills the growth and rinses it away without blasting the siding. Scrubbing or high pressure only knocks the top layer loose, and the green comes back fast.
Drive through Central, Denham Springs or Zachary after a wet spring and you'll see it. The north side of the house goes green while the front still looks fine. Big trees, close neighbors and thick shrubs keep walls in shade, and the humidity rarely lets them dry out.
What the Green Stuff on Your Siding Is
That green film is alive. It's algae, often with mildew mixed in, and it grows on the siding the same way it grows on a shady fence or a birdbath.
It isn't dirt, so it doesn't rinse off like dirt. The growth holds on to the surface and keeps spreading from the spots where it started. That's why the problem gets bigger every season if nobody treats it.
It shows up on vinyl, wood and board-and-batten siding, and on brick and stucco too. Painted trim, soffits and porch ceilings collect it as well. Once you know what it is, the next question is why your house has so much of it.
Why Baton Rouge Siding Goes Green So Fast
Algae needs water and shade, and this part of Louisiana has plenty of both. Baton Rouge averages 61.94 inches of rain a year, based on NOAA's 1991 to 2020 climate normals.
Rain is only half of it. Siding that never gets direct sun stays damp for days after a storm. These are the spots where green shows up first:
| Where it shows up | Why it starts there |
|---|---|
| North-facing walls | They get the least sun, so they stay damp the longest |
| Walls under big trees | Shade, plus water dripping off the leaves |
| Behind shrubs and beds | Moisture is trapped against the bottom of the wall |
| Near sprinkler heads | The siding gets wet every time they run |
| Under gutters | Overflow runs down the same strip of siding again and again |
If your house has two or three of these, expect green on those walls first.
So the green isn't a sign you did anything wrong. It's what happens to siding in a wet, warm place. What matters is how you clean it, because the wrong method makes things worse.
Why Scrubbing and High Pressure Don't Fix It
The quick fix most people reach for is a pressure washer from the hardware store. It looks like it works, but it causes two problems.
First, high pressure can damage siding. The vinyl siding trade group warns against aiming a power washer upward, because it can force water behind the panels. Some siding makers don't recommend power washing at all.
Second, blasting or scrubbing only knocks off the top layer. The growth that's left behind is still alive, and the green comes back fast. That's why a house can look clean in May and green again by fall. Our guide to soft washing vs pressure washing goes surface by surface.
How a Soft Wash Gets Siding Clean
A soft wash cleans the house at low pressure with a mix made for the surface. The mix does the work, killing the algae and mildew instead of blasting them off. Here's how we run it:
- Look at the job, so you can point out the spots that bother you
- Cover the plants and seal the outdoor outlets
- Move anything sitting on the driveway, walk or patio
- Mix the wash for your surfaces: vinyl, wood, brick or stucco
- Apply it at low pressure, give it time to work, then rinse
- Take the covers off, water the plants and put your things back
You can read more about the method on our house soft washing page, and how our quotes work covers pricing. Once the siding is clean, a few habits help it stay that way.
How to Keep Siding Clean Longer
You can't change the rain, but you can take away some of the shade and water the algae lives on. Roofs pick up a cousin of the same problem; see what causes black streaks on a roof.
- Trim shrubs back so they don't touch the siding
- Point sprinkler heads away from the walls
- Keep gutters clear so they don't spill down the siding
- Cut back branches that hang over the roof and walls
- Wash as soon as green starts to show on the north side, before it spreads
Those habits slow it down. When the green shows up anyway, it's time for a wash, and the questions below cover what people ask us most.
Green Siding Questions From Baton Rouge Homeowners
These are the questions we hear most when someone calls about green on their house.
Is green algae on siding bad for my house?
At first, it's mostly cosmetic, but it keeps spreading, and it can hold moisture against the siding. It's easier to clean when it first shows up than after it has covered a whole wall for a few seasons.
Can I pressure wash green algae off vinyl siding myself?
You can, but be careful. Vinyl siding's trade group warns that aiming a power washer upward can force water behind the panels, and some siding makers don't recommend power washing at all. High pressure also leaves living growth behind.
Will the green come back after a soft wash?
Over time, it can, because the rain and shade that caused it are still there. A soft wash kills the growth instead of just knocking it loose, so it stays clean longer than a blast with high pressure does.
How often should I wash my house in Baton Rouge?
It depends on shade, trees and sprinklers. Houses with a lot of shade show green sooner. Watch the north side and the walls behind shrubs. When green starts to show there, it's time for a wash.
Does a soft wash work on brick and stucco?
Yes. A soft wash is the method we use on vinyl and wood siding, brick, stucco and painted trim. The mix is matched to the surface, and the pressure stays low on all of them.
How much does it cost to wash a house?
Every house is different, so we give you a free quote first. The price depends on the size, the number of stories, the surfaces and how much growth there is. Once you approve the quote, that's the final price.
About the author
Jaylan Gerald
Owner, Gerald Washing Solutions · Firefighter · Central, LA
Jaylan Gerald is a firefighter and the owner and operator of Gerald Washing Solutions. He soft washes houses and roofs, pressure washes driveways and cleans windows across Central, Denham Springs, Zachary and the Baton Rouge area.
This article is written from how Jaylan cleans houses, roofs and concrete on the job. Outside facts link to where they came from:
- NOAA U.S. Climate Normals, 1991 to 2020 (Baton Rouge)
- Polymeric Exterior Products Association: How to clean vinyl siding
More about JaylanCall (225) 503-5675
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