Voila! Mulch on top of the cardboard, the tree in the center. Almost done. The tree is leaning, my error, but I will right it with a stake and the roots will do the rest. The ground is soaked so I won't water for weeks. When I have to water I'll put a hose at the hole in the cardboard and let it trickle. The mound of dirt will spread the water.
OK? That's how I plant young trees that have been in a container a bit too long.
By the way that's bark mulch that's been wet too long and turned dark naturally. From its own tannins, I think.