Allotments 4 All

not sure if this question should be here or in the non-edible section, but here goes....

I've been given a large salix Flamingo 8) - the tree not the bush. It had been in a large pot on a south-facing terrace and the north side of the trunk & some stems have a mossy growth. I intend to plant it in the open ground although I could replant in a tub and turn it if this would help it?

Do I need to treat the moss? If so, with what? Is the moss a sign of general disorder or is it there only because the tree has always been in the same position?

Many thanks for any suggestions/comments.