Why the North Wall of a Florida House Turns Green

The north side of a house in Tampa Bay gets the least direct sun, so it stays damp longest after rain and morning dew.

Algae and mildew love that. A thin film starts within a few months and turns green or black within a year.

Rinsing it with a hose only moves the surface layer. The roots stay in the pores of the stucco and the color comes back in weeks.

A soft wash kills the growth at the root, which is why a properly washed wall usually stays clean for a year or more. Trimming shrubs back from the wall helps it dry faster too.