Can you build a sort of cold frame? Like a metal wire frame upon which you can place some layers of transclucent plastic. Then bury the pots into the soil and mulch. You want to keep the snow, ice and wind off of them over winter. Your shed will likely stay too cold. You want those pots buried into the soil so that the soil in the pots doesn't freeze and thaw so quickly like they would in a shed.

mattp321,

to begin with you've done a great job with your WM seedlings, they're twice as big as mine. NoVA Dave has given you good and accurate advice. WM is evergreen so it must have some light in the winter.

If you have no other options, plant your WMs, pot and all in the ground and mulch well. This method protects the roots from the frigid air temps.

Thanks for the tips. I can bury them and maybe make a pvc pipe frame over them with some plastic sheeting draped over... Not sure how they will get rain water with that on top...???

Thanks for the compliment, but to be honest I ignored them most of the year... Just watered when I remembered.

Just water them well before 'sealing up' the plastic. Check during periodic warm-ups (if there are any!). You shouldn't have to worry too much about them drying out.