So far, in the various WS gardening sites I've checked out, I've only seen one person saying that Promix Ultimate worked well for them when they did winter sowing. Has anyone else had success using this particular potting soil for winter sowing? ( My main concern is that the Promix package says the mix contains 'water saving gel'--and since I've read numerous times that 'moisture control' Miracle Gro SHOULDN'T be used for WS, I'm wondering if that is the same ingredient that would make Promix Ultimate also unsuitable for winter sowing?)

I use pro-mix all purpose mix or seed starting mix on top but I put miracle grow moisture control on bottom for winter sowing. I sometimes don't get to my winter sowing jugs until fall And plain promix dries out easily and can be hard to rehydrate.

But I have never used moisture control on top. So not sure how that will work.

I've used a moisture control formula successfully for winter sowing. Like Jennifer stated, it really helps if you fall behind on planting out, too. If a prolonged wet weather event finds you concerned, you could provide some cover for the duration.