Since fences are built of different materials, they can be organic or inorganic.
Organic materials gives spores nutrition and therefore the moss' growth
Fences is exposed to weather and wind and therefore exposed to large amounts of moss spores. They attach themselves everywhere and fences offer many spaces, joints and fissures where dirt and damp gives the moss nutrition.
When the affections have established themselves, they will reoccur until the fence has been sterilized and disinfected –in every little pore- from all spores and old moss. Thereby all growth of moss is guaranteed to be prevented for four years.