Spinach is very hardy. Territorial Seed Company has some varieties that are extra hardy. They will over winter with very little protection. I don't give my spinach any protection and they survive all winter. But our lowest temps are usually in the low teens. I wouldn't bother put spinach in pots. I put them straight in the ground. But then again I usually plant a few hundred plants.
Kendra

Adenn1.....I have the same idea---I have two 4' long 'hayrack' planters on the side of my garage, fairly sheltered, but sunny in the afternoons. I thought I'd put them to use over the winter by growing spinach and dwarf carrots. I might keep a couple of pieces of row cover handy to cover them up if the weather gets really cold (not a frequent occurrence here in Central VA), but otherwise not give them additional protection. I also have a small coldframe where I can grow a few things as back-up, in case my experiment fails!

Good luck!

I plan to start the spinach in the containers in the next week or so--I believe I should wait till weather get a bit cooler. Will let you know how it turns out...

Thanks...