We've had cold days followed by warm days. The seeds would germinate and then when it freezes again, the plants would die.

I tried winter sowing one year and to tell the truth, I'd rather tend plants in my pj's, indoors under lights.

kitasei, I've sown some perennials that I know need a long period of moist chill before they will germinate. The solstice is supposed to be the formal starting date, but who has time with the holidays. The last thing my kitchen needs right now is pots, labels, buckets of dirt ;0)