The 21st of September is traditionally the day in the fall to go off “nutting” and gather fall nuts. “Nutting” also afforded an occasion for teenage boys and girls to go off into the woods unsupervised, and to engage in a whole different sort of nutting altogether.
It was believed that Sundays were a bad day to gather nuts, because you might meet the devil doing the same thing on a Sunday (because he, like you, wouldn’t be in church, where you were supposed to be.)
The 21st of September, however, was safe to gather nuts because on this day, the devil had been out gathering nuts when he ran into the Virgin Mary in the forest. He dropped his bag of nuts and fled.
In Alcester, Warwickshire, England, there is a hill called The Devil’s Nightcap, which local legend said was formed by the bag of nuts that he dropped.