Moss and mould growth on trees most often occurs when the trees are heavily shaded. The mould is typically a fungal growth known as lichen. While harmless, moss and lichens on a tree may be undesirable for cosmetic reasons. Fortunately, this type of growth occurs only on the surface of trees, which makes the removal process relatively easy. To get the best results, remove moss and mould at the appropriate time of year.
Wear garden gloves, and pull off as much moss as you can. Depending on how high it grows, you may be able to pull it all off by hand.
Mix a solution of 1 part bicarbonate of soda to 20 parts water in the tank of a garden sprayer. Shake the tank until the soda powder dissolves into the water.
With the garden sprayer, spray the soda solution on the moss and mould until they are thoroughly saturated. The solution will kill any mould on the tree.
Apply fertiliser to the base of the tree and the soil surrounding it to boost the tree's health. For best results, use a fertiliser made for your particular species of tree. As a general rule, you should apply 500 grams of fertiliser for every 3 cm of the tree trunk thickness. For example, if the trunk is 18 cm thick, you should use 2.5 kg of fertiliser.
Remove the moss and mould in winter during the dormant stage of the tree.
Apply fertiliser in early spring when the tree comes out of its dormant stage.
If you have access to a power washer, you can use it to remove moss and mould in hard-to-reach areas. Use low pressure to prevent damage to the tree. Power washers should only be used on well-established trees.