On average how thick should the mulch be around a young tree.

Start out with 3 to 4in. because it will settle. After it settles a couple of inches is usually enough. Sort of depends upon what you're using for mulch, too. You want it thick enough to both insulate the soil and keep the sun out so weed seeds don't germinate.

Be sure not to pile it up around the trunk of your little tree. Start the mulch an inch or two away from the base, and mulch outwards well past the reach of the branches. As it grows, extend the circle. Most trees have feeder roots out beyond their drip line.

I forgot to say Thank you!

Wallflower;

I would add to Dyzzpyxxy's very good advice by suggesting wood chips and topping them off every or every other year. If you have and mow your own grass I'd put that down first and continue as the tree grows.I'm in front of my T.V. listening to the news while writing this and I hope you're far away from these fires I'm hearing about. Good luck and be safe.

Yes! Thanks, J.R. I forgot to say that wood chip mulch is the best, and not to use anything like rubber or rocks because they absorb heat, don't hold water and don't insulate the root zone well at all, plus they sink into the soil and cause many headaches later.