the Persephone begins
Today marks the beginning of the Persephone in my area. This is the date when Persephone, the vegetation goddess, returns to Hades and causes the earth to become barren and wintry. I guess she stays toasty, but not us. While she's gone, our plants don't have enough sunlight to grow. With some cold protection, our plants will hang out and wait for her return when they can grow again.
So the Persephone is the time when there's less than 10 hours of sunlight each day. Most plants need more than 10 hours to grow. Their growth is slowed or stopped, even if winter temperatures are mild.
Persephone dates vary according to your latitude. In my area near Boston MA, it starts today, Nov 10, and ends Feb 10. In Kentucky, it starts Nov 22. To figure out when the Persephone starts in your area, you can keep an eye on the vegetation goddess. There are also tables on line where you can look it up. The Univ of Nebraska Day Light Explorer is a really cool interactive graph to explore different daylight hours at different latitudes.
source: Mother Hubbard "Calculating Your Persephone Days"