Why Does Siding Turn Green in Jacksonville?

Meet Gloeocapsa Magma: The Green Culprit

The green — and the black streaks often mixed with it — is usually Gloeocapsa magma, a blue-green algae that thrives in warm, humid climates. It feeds on moisture and organic material, spreads through the air, and colonizes siding, stucco, brick, fences and even concrete. Jacksonville's year-round humidity makes it a permanent resident.

It starts on north-facing walls and shaded areas, then spreads. What looks like a little discoloration this spring becomes a full green wall by fall if ignored.

Why Scrubbing and Rinsing Don't Work

Algae anchors into porous surfaces with microscopic root-like structures. A rinse — or even high-pressure water — shears off the visible top but leaves the roots. Within weeks, it's back, often worse, because the disturbance spreads spores.

This is the core reason soft washing exists: the cleaning solution kills the organism down to the root, then a gentle rinse removes the residue. Treated properly, siding stays clean for years, not weeks.

The North-Side Pattern (Check Yours Today)

Walk around your home and compare sides. In Jacksonville, the north and east elevations — the ones that stay shaded longest — almost always show growth first. If those walls are green or streaked while the sunny side looks fine, that's textbook algae colonization, not a siding defect.

The same pattern shows up on fences, garden walls and the shaded half of driveways. Wherever moisture lingers, algae follows.

Prevention After the Wash

After a proper soft wash: trim vegetation back from walls for airflow, redirect sprinklers that spray the house, keep gutters clear so overflow doesn't streak siding, and plan on a maintenance wash every 1–2 years. You can't change Florida's humidity — but you can deny algae the foothold it wants.

Frequently Asked Questions