I'm in East Tennessee where January could bring balmy 60s and March can bring 23" of snow. So I figure to give this more of a chance of success, I'll stagger my sowing, January 1st, February 1st, and March 1st.
I've got a bale of ProMix and my plan is to sew directly into 2.5-qt plastic pots, filled 3/4 of the way to the top with "soil". I don't plan on greenhousing each pot or any of the pots... winter doesn't do that. But if I panic and decide to later, I've got room above the soil to put plastic over each pot.
I'll put one kind of seed per pot, 1/3 of total of that kind of seeds/pot.
I'll have pots in three different locations because I'm not sure which will be best here -- the south side deck, under pine trees or, in direct sun... figuring, SOMETHING should live with the various locations...
With three locations and three "sowings" this could possibly give me 9 pots of each kind of plant... cool.
Heeheeheee, Good Morning "Long Time Listener"! < =)
The first, and very most important thing I can suggest to you is to always remember: ENJOY YOURSELF! You'll be playing in the dirt, what can possibly be better than that? < =D
After you are prepared to Enjoy Yourself (yes, Capitalized), I would suggest you start sowing right before the soil in your containers is ready to get frozen... don't want those little suckers to germinate too soon then freeze to death. A good clue as to whether it's "really" winter in your area: The deciduous trees have finally lost ALL their leaves. For you, this might not be until the end of January or middle of February. So be it. Fill your pots with their soil, put 'em into place where you're going to want them, then start checking them from time to time when you think it's close to time for them to nearly be freezing. Gonna have to stick your little fingers down into the dirt, but HEY, that's part of the fun! =) Gotta get dirty if ya wanna have fun, right? Right.
Ok, so,... let's say you get a little forgetful (like me), and suddenly 3 weeks go by and you've forgotten to check.. then you go outside and all the soils in all your little pots are frozen! DON'T PANIC. Easy peasy. Spread a thin layer of room-temperature soil across the top of the frozen soil, sprinkle your seeds, pat gently down into place to give the seeds good contact with the soil (think "snuggle"), then, if they're seeds that need covering, sprinkle a thin layer of that room temperature soil on top of the snuggling seeds. For the pots that are in a "protected" area (like under the pines that you mentioned), LIGHTLY water with a watering can. Just a little bit, God will do the rest for you during the rest of the Winter. For the "exposed" containers, more open to the elements, you don't have to water at all, but you may LIGHTLY mist with a spray bottle if you like. Just a little bit.
That's it. Nature will do all the rest for you.
The "Big Idea" of "winter sowing" is to provide a bit of protection to the seeds, while still giving them all the benefits of being out in the natural 'Great Outdoors'; nature will take care of stratification etc. The back-and-forth activity of freeze-thaw-freeze-thaw is what stratifies the seed shells naturally, so you won't have to worry about "nicking" or "filing" the seeds; and since they'll be outside, you shouldn't have to worry about watering either, unless you have a particularly warm/dry Winter. (like we had last Winter).
I've not done winter sowing in the manner you're doing it, strictly because I have such a huge population of squirrels in my area that, no matter what I do, they dig it up. I've been using hair in my containers with success... until just this Fall. Now, they even dig into those pots that have clumps of hair in them, so any winter-sowing I may do will all be done the "old fashioned" way, in covered jugs etc on my deck (where I can POP out the door and scare the squirrels to death, or chase 'em with my kitchen hatchet, heh heh).
That being said, those simple little 'common sense" tidbits should help you along the way. < =) Keep in mind that, with containers being more open and exposed to Nature and the elements, there will be more opportunities for .. uuhh... natural difficulties, like birds and other critters to get into your seeds, not to mention heavy rain washout, or God forbid, really heavy weather conditions causing container-wash-away! Eeeek! Just a tiny little bit of diligence will take care of that though, so DON'T PANIC. =)
Winter Sowing is what got me HOOKED on gardening to begin with, so I will assist you in any way I can, and I hope I've been of some help so far. When I first got started I was scared dirtless. ;) Then, once I jammed my iPod into my ears and got started, I was too busy boppin' along with the dirt flyin' everywhere... got so carried away, I was having too much fun to be nervous anymore! Get some good music flowin' and HAVE A BALL! < =D Come across a question? Please bring it here, I, or anyone here, will be super dooper happy to help you!