Xeramtheum, we've all had that happen occasionally. Consider, it's currently 24° here. But by Friday, it's supposed to be 59°. Keeping containers in shade does help to prevent premature sprouting. Also, I only wintersow perennials at this time of year. They tend to take a little longer to sprout anyway. For annuals or tender perennials, I use the same method, milk jugs outside, but I don't sow them until around March or April. Then for frost after they germinate, I just throw a blanket over them overnight.
Customizing the method a little bit this way really does limit a lot of problems. This will be, I think, my 8th year wintersowing.
Karen
