Weird soil problem

[hoodat]

You will more than likely have mushrooms popping up when it matures, The threads are actually the fungus, Mushrooms correspond to the flowers in the higher plants. They bear the spores for new plants. Once the mushrooms show up you will be able to identify it.
If you bought it more than likely it was someones spent mushroom culture; actually excellent organic matter once it is fully spent. It will be well rotted horse manure.

 

[journey11]

You'll probably have tons of little mushrooms popping up everywhere next year. It can look disturbing, but they won't hurt anything (unless you have to worry about little ones trying to eat them.) I had been following a group for the BTE garden method that @Beekissed uses and as the mulch breaks down, they often see a lot of mushrooms show up there doing their job. If you're lucky, it might have been someone's used mushroom compost from cultivating something yummy like oyster mushrooms! My FIL used to have morels pop up in his rose garden mulch occasionally. That was cool.