Questions: for this zone, and these varieties, is sowing at solstice detrimental? I saw something about rot with early sowing. Do you water after the initial sowing? Any favorite mix? I like the gallon milk cartons, but do clamshells work or are they too shallow?

I'll take a stab, anyway. The seeds you listed don't need to be sown on the solstice. None of them really need stratification - well, maybe the English wallflower needs a little. Petunias and marigolds, in my experience, can be sown later; the sweet pea seeds could rot if left wet and cold for too long a period of time. If you really want to sow on the solstice, I'd probably choose the wallflower and the creeping thyme - leave the others until later (early March or so).

Watering after the initial sowing really depends on your weather conditions and where you keep your containers. If you can put your containers out into the elements, where they can get snowed on and rained on, etc., you probably won't need to water again until the weather starts warming up and seeds are sprouting. If the containers are in a more protected area, you might have to water at some point; a bottom-watering is best.

Soil? Most folks use Miracle-Gro, Pro-Mix, Fafard (my choice) or some other soil-less potting mix. Others make up their own mixes. The important thing is that whatever you choose should drain well.

As for clamshells - ditch 'em! Too shallow. Gallon milk jugs are the container of choice - by far - but anything that can hold at least 3-4 inches of potting mix can be used.

Hope this helps - and welcome to Winter Sowing!

PV