Beauty! Polyporus umbolatus. Not sure exactly what they grow with but always in mixed wood. Delicious edible even though its quite uncommon. We get it in the Edmonton rvier valley in very wet years.
I think it is saprophitic as I have seen it grow on ginger root people have thrown on the ground. I assume for exactly that reason. Maybe try going back and put some ginger root on the ground where they were growing.