I think it depends.

Moss likes acidic, low pH. Wood ash is potash, and is higher pH, alkaline.

Looked on Google:

How to grow moss: http://www.mossandstonegardens.com/blog/how-to-grow-moss/

Then I came upon how to grow morel mushrooms...

- Brian

The composite decking on my little porch is deteriorating, and does get slick.