Winter sowing is all about giving some seeds their chilling period. This is called stratification. Note that not all seeds need to be in cold all winter, but if you want to plant them in November you can do so. I typically put my poppy seeds out in February and they have their required cold time between then and when they sprout in May.  I also sow any flats of seeds that benefit from chilling in February. I will cover those with floating row cover (seen on the pots in the postcard, and available at local garden centers) and place the flats out where they will get light and rain. In March I will pull those into my solar-heated seed starting shed where they will sprout. 

I have found that this tall Verbena bonariensis benefits from stratification, but once you have it in your gardens, it usually does this by itself. I don’t have to start verbena seeds anymore since they self-sow in my gardens. 

This blog has a nice roundup of information about stratification, along with a list of plants that need a chilling period. If you’re in doubt about the seeds you want to start, just goole their name and the question.