The wood's organic components are resin, damp and wooden fibres, which contains
nutrients that furthers establishment of the moss' spores.
When the spores have become attached to the wood surface –treated or untreated- they get nutrition from the damp that has been gathered there. If the fence is dirty or has old remains of growth, there is even more nutrition for the moss. The development goes fast.
Moss is quite hard to get rid of. It requires sterilization of all spores and remains of vegetation. When the treatment with Bensaltenside has been made, the wooden surface is disinfected and recurring and new growth by moss is now impossible. Protection is guaranteed for four years –often longer.