Why your vinyl siding turns green (and how to keep it from coming back)

You wash the house. Six months later the green is back. What gives?

That film is a mix of algae, mildew, and lichen. Middle Tennessee's humidity and tree cover create perfect growing conditions, especially on north-facing and shaded walls.

Blasting it off with high pressure is like mowing a weed instead of pulling the roots. The visible stuff comes off, but the microorganisms are still embedded in the vinyl's texture. In a few months you're back to square one.

A proper soft-wash uses a sodium-hypochlorite based cleaning solution. It doesn't just remove the green — it kills the organisms at the root. That's why a soft-wash lasts 12–18 months and a "pressure blast" lasts 3–6.

• Overhanging trees and shrubs (trim them back 12 inches from the siding)
• Sprinklers hitting the siding regularly
• Poor drainage that leaves mulch/soil pressed against the base

I recommend a soft-wash every 12–18 months for shaded houses, every 24 months for sunny homes. In between, if you spot early green film, a hose-and-brush spot treatment prevents it from spreading.