Since every year's weather is so different, I take clues from the weather. When temps start warming, and the forecast shows no brutal freezes, I do annuals. For me, that's usually sometime in March. Sometimes I've waited until around April first in particularly cold years.
Most annuals germinate more readily than perennials. When they get a little warmth and longer days, they know to sprout. And the milk jugs work like little greenhouses, raising the inside humidity and temp higher than ambient air temp. And if we get a late hard frost, after they've germinated, I close the jugs and throw a blanket over them (annuals) overnight. Perennials usually do OK on their own in closed jugs.
Wintersowing seems a lot less scientific than indoors under lights, but the seeds seem to figure it out. I always have some jugs that don't sprout, or have a low germination rate, but most do very well.
Karen
