Sawdust as mulch and myco

[svalli]

I have used the MycoGrow soluble for all my potted plants, in my garden and flowerbeds. I planted new hostas early May and put MycoGrow directly to the planting hole. The area was mulched with coarse sawdust previous fall. I noticed now that there are mushrooms growing next to the new hosta. It could be from the MycoGrow or some local mushroom (I am not good identifying them), but anyways sawdust seems to be good mulch for mycorrhizal. We cut some trees for firewood this week, so I spread the fresh sawdust under my zucchini and over a flowerbed. I have read that sawdust is not good mulch, because it ties nitrogen from soil when it decomposes and that's why I hesitated earlier using it.

I hope I'm doing the right thing.