Persephone

The Persephone period is the time of year when growing light hours fall below 10.  It is named for the time of year when the Greek goddess Persephone visits the underworld and her mother Demeter is stricken with grief.   

Below 10 hours of growing daylight, plants generally become dormant and cannot put on new growth or produce fruits or flowers.  This is true, regardless of the ambient temperature.  For example, even in a greenhouse where the temperatures are regulated, in the dark of winter, plants generally do not grow during the Persephone period without supplemental light.

 

In Virginia: 

On October 11th, sunrise is 7:25 am and sunset is 6:25 pm for a total daylength of approximately 11 hours.  

The threshold of 10 hour days is typically when plants stop growing and developing.  On October 31st, daylength is approximately 10 hours.  Actual daylight hours, including twilight, is about an hour longer.     

On December 21, day length is 8:23 hours long in Virginia, the shortest day of the year.  On February 10th, daylength again crosses the 10 hour threshold when the most cold-hardy plants begin growing again.

Note that this is different from temperature patterns, where February is typically the month of the year with the greatest potential for winter snow.