My best results have been by covering with brush, then a layer of row cover or some sort of light fabric. Weigh down the edges and hope for good snow cover. The goal is to keep anything from directly laying on the spinach, and maintain some air space.

Steve

It overwinters here in MN so you should have no problem at all.

I have never done anything special with various types of spinach in the winter and it so far has always survived. Usually by April it starts producing in abundance.

really? in z4 with no protection?

It shouldn't need any protection in your zone, except maybe from hungry deer (I've heard they're all over the D.C. suburbs). One easy thing to do is clip branches from one of the Christmas trees that get put out for recycling, and lay them over the spinach for a bit of protection as we go deeper into winter.

That was a good method, Elisa. Thank you. I did similarly with my tarragons.