Demeter's broken heart
" Persephone, did you eat anything while you were down there?"
"No, I was too tired to eat,all I had was 4 pomegranate seeds."
Zeus says, " How about instead of spending eternity in the underworld, you just spend one month for every seed you ate."
So Every 4 months,when Persephone goes to the underworld, I greave and morn, and don't let anything grow. This is why there is winter