It always feels like a weather switch is toggled over on September first. Mornings and evenings are cooler, if not downright cold feeling. There are a few leaves here and there that are turning colors and fluttering down from the trees. There is just a different feeling in the air - as if nature has given its all for the last several months and it is ready to start relaxing as well.
A sure sign of fall on a mushroom farm is when the Nameko start growing!
I don't think of Lion's mane as especially growing in the fall (we do pick them on and off throughout the season) but a lot of them are coming on right now. So they must like the slightly cooler weather!