A green film on a greenhouse surface is consistent with persistent wetness, but it does not prove that condensation caused the water. Light, mineral nutrients, debris, irrigation paths, and the surface itself can all change what grows. Treat the film as a location-specific clue rather than proof of algae, a fungal disease, or inadequate equipment.
Water, light, and nutrients create the context
UConn Extension describes algae as organisms that need water, light, and mineral nutrients. In commercial greenhouses, irrigation, misting, runoff, puddles, and condensation are different possible water paths. Plant debris can supply nutrients. On growing media, algae can form a crust that interferes with water penetration; growth on glazing or walkways presents different concerns. (UConn Extension)
Green film is not a complete identification
The Royal Horticultural Society describes algae on greenhouse glazing and floors as a green film or powdery deposit, often in damp, shady areas. It separately describes liverworts as flat plates and mosses as cushion-like growths. These visual distinctions help organize an inspection, but appearance alone is not a species diagnosis. RHS also notes that growth on glazing can reduce light and that films on floors can become slippery. (RHS)
Water systems can tell another story
Oklahoma State Extension discusses algae in shallow, stagnant, nutrient-rich water and connects that setting with irrigation or pump clogging and shore flies or fungus gnats. This is a water-system pathway, not evidence that a green film on glazing came from condensation. A surface film and a reservoir or irrigation problem may coexist while having different sources and implications. (Oklahoma State University Extension)
Trace the surface and the re-wetting event
For a useful handoff, record the surface, location, shade, visible film form, nearby debris or nutrients, and whether re-wetting follows irrigation, misting, runoff, pooling, or visible condensation. Compare those observations with the local air reading, without turning the reading into a cause. For broader airflow context, see practical techniques for optimizing greenhouse ventilation. Share the record with the facility or crop team.
Related project questions
For other locations where moisture may persist, compare mold on greenhouse structural surfaces and uneven crop humidity zones. For the wider project context, return to agricultural humidity control.
