Have you ever looked up one of the many Zone 4 planting guides available on the web? I linked one below. It is a general planting guides but most find ti helpful.

If you aren't comfortable with it then narrow your zone down to 4a or 4b and Google for '4a (or b) garden planting guide'.

Dave

Here is a link that might be useful: Zone 4 Planting Guide

Hey thanks and I read some follow up discussions on this topic, too.

Root crops are better than other crops. I have harvested carrots in December and January (nicely mulched after the first freeze).