Identifying and Managing Lichens on Outdoor Wood Structures

What Is That Green Flaky Growth on Your Playset?

If you've noticed a green, flaky coating on wooden outdoor structures like swingsets, fences, or decks, you're likely looking at lichens—not mold or a harmful microbe. Lichens are a symbiotic partnership between fungi and algae (or cyanobacteria) that can grow on almost any stable surface, including wood, stone, and bark.

Understanding Lichens

Lichens come in three main growth forms:

• Crustose: Tightly pressed against the surface, appearing as a crusty layer. This is the type commonly seen on playsets.
• Foliose: Leaf-like, with lobes that lie flat but are loosely attached.
• Fruticose: Shrubby, upright, or hanging forms.

Lichens lack roots and absorb moisture and nutrients directly from the air. They thrive in damp, humid climates and on surfaces that stay moist for extended periods—such as wood shaded by trees.

Are Lichens Hazardous?

No. Lichens are not parasitic and do not damage the wood structurally. They are not toxic to children, pets, or wildlife. The flakes that brush off are simply fragments of the lichen body (thallus), similar to dried leaves. However, heavy lichen growth can make wood look unsightly and may indicate that the wood remains damp, which could eventually promote decay fungi.

Safe Removal Methods

If you prefer to remove lichens for aesthetic reasons:

1. Pressure washing: Use a low-to-medium pressure setting to avoid damaging the wood. This effectively removes most lichen growth.
2. Bleach solution: After pressure washing, apply a mixture of 1 part household bleach (sodium hypochlorite) to 10 parts water. This helps kill residual spores and brightens the wood. Rinse thoroughly after 10–15 minutes.
3. Wood sealers/preservatives: Once the wood is dry, apply a quality water-repellent sealer or wood preservative. This reduces moisture absorption, making the surface less hospitable to lichen regrowth.

Safety note: Wear eye protection, gloves, and a dust mask (N95 or better) when pressure washing or handling bleach. Ensure good ventilation.

Alternatively, Do Nothing

Lichens pose no health risk and will not cause the wood to fail. If the appearance doesn't bother you, leaving them is perfectly fine. Over time, the wood may darken and look weathered, but it will remain structurally sound for years.