I don't know the answer, but you might want to try the seed saving forum if you don't get an answer here.

Here is a link that might be useful: seed saving forum

Viable seeds will sink. You have to be careful with this though. Really small seeds will float even when viable.

Though it's supposed to be that viable seeds sink to the bottom, I've found that floating morning glory seeds and sweet pea seeds and moon vine seeds always germinate for me when I WS them.

Usually there is no need to soak most seeds before wintersowing them, but I've found, now doing 8th year of WS, that I have just about 100% germination with my MG seeds if I soak them overnight first.

I also found near perfect germination if I surface sow sweet pea seeds.

Never soak overnight any other seeds though, and WS all my seeds with near 100% germination with all my containers.

What seeds did you soak overnight?

Fran

Thanks for the information
I soaked datura seeds A lot of them were floating but I planted them all anyway.Tonight I'm soaking hibiscus seeds.

Your datura seeds are not going to germinate until the soil temps are at least 65 degrees.

Neither datura or hibiscus seeds need to be pre soaked before WS them or even sowing indoors under lights.

Fran