What Causes Green Algae on Wood?
Green algae grows on wood that stays damp in shaded, humid spots. It's a common sign that moisture lingers on the surface — and that the wood needs care.
Why algae appears
Algae needs moisture and light-avoiding shade. Decks and fences under trees, on north sides, or against the house can stay damp long enough for green growth to establish — especially in humid climates.
What it means for your wood
Algae itself is mostly surface buildup, but it holds moisture against the wood, and in humid conditions that environment can also invite mildew and rot over time. It's a sign the surface isn't staying dry and isn't being maintained.
Removing and preventing it
Professional cleaning removes the growth and prepares the surface, and a protective finish helps the wood shed water rather than absorb it. Improving air flow and shading, and keeping debris off the wood, all reduce the conditions algae needs.
Quick answers
Will algae damage my deck?
Algae is mostly surface buildup, but it holds moisture against the wood, which over time can contribute to mildew and weathering. Removing it and finishing the wood helps.
How do I keep algae from coming back?
Reducing moisture, cleaning and finishing the wood, and keeping shaded spots free of debris all make the surface less welcoming to algae.
Not sure where to start?
A restoration consultation looks at your wood and recommends the right care. We respond within one business day.