During
damp conditions, moss and algae can grow on hard surfaces such
as paving and walls. This can make these surfaces slippery and
dangerous.
Control
Reducing the appearance of moss and algae is the first step.
Increase light by pruning back overhanging branches of trees and shrubs, which will also improve air circulation to dry out surfaces in damp areas.
Regular brushing with a stiff brush can help prevent severe infestations. Gravel should be raked regularly.
Improve drainage in surrounding areas if water lies on the surface for any length of time.
Removal
A pressure washer will help remove even the worst of moss and algae from surfaces but the water should be able to drain away freely.
Chemical control consists of non-pesticide cleaning products specifically for paving or moss and algae killers containing pelargonic acid (Finalsan Moss & Algae Killer). Do not use lawn mosskillers on paving as some kinds will leave a stain.