From what I read you can start sowing on the winter solstice, Dec 21st and after. I guess a lot of people wait to sow their annuals until Feb/March. You don't only have to sow seeds that need stratification. You can winter sow nearly everything, with exception of Tropicals. And yes, you can winter sow Hosta's. This will be my first year doing it and I'm going to winter sow nearly everything that I have. There is a great forum on GW and tons of people that have done it. Take a look. Less than a month to go!