Green Algae on Siding and Stucco
A green cast on the north wall, darkest near the ground and under the eaves, is the most common exterior complaint we get in Central Florida. It is also one of the fastest to fix.
What causes the green film
Green discoloration on siding, stucco and painted block is algae — usually a mix of green algae and mildew that establishes anywhere a wall stays damp long enough for spores to settle.
It concentrates in predictable places: the shaded north elevation, the lower two feet where irrigation spray lands, under soffits where dew collects, and behind shrubs planted tight to the wall.
On stucco it works into the texture, which is why a quick rinse only lightens it. On vinyl and painted surfaces it sits more on top, but it still needs a cleaning agent rather than force to remove properly.
Why it comes back so fast here
Central Florida gives algae everything it needs — humidity that rarely drops, daily convective rain through summer, and no freeze to reset growth.
Irrigation is the factor most homeowners miss. A sprinkler head throwing onto the wall two or three mornings a week will regrow a green stripe within weeks of any cleaning, no matter how well the wall was washed. We flag misaimed heads when we see them.
Landscaping planted close to the house has the same effect, trapping humidity against the wall and blocking the sun that would otherwise dry it.
What not to do
Do not attack it with a pressure washer. On stucco, high pressure chips the finish and drives water behind it. On vinyl it forces water up under the laps into the wall cavity, where it causes far more expensive problems than the algae did.
Do not scrub painted surfaces. Mechanical scrubbing burnishes and dulls the paint, leaving a patchwork that is more visible than the algae was.
Do not treat only the visible patch. Spores are already established across the whole elevation. Spot-cleaning produces an obvious clean rectangle and regrowth around it within a month.
How we clean it
We soft wash the full elevation — low pressure with a cleaning solution that kills algae and mildew at the root, applied evenly so the wall cleans uniformly rather than in patches.
Windows, screens, light fixtures and door hardware get rinsed as part of the wash. Landscaping is pre-soaked before we start and rinsed again afterward.
Because the organism is killed rather than knocked loose, a soft-washed wall stays clean far longer than a pressure-washed one — typically a year or more where irrigation is not hitting it.
Questions we get about this
Will soft washing damage my paint or stucco?
How often does a house wash need doing in Central Florida?
Can you clean stucco without leaving streaks?
Does this include the screens and windows?
Related: Outside house washing · Soft washing explained · all FAQs