Can i plant bok choy in zone 3....
yes, you should be able to, they are a cool weather crop.
you can start seeds in a shallow tray in a small greenhouse or next to a south facing window inside. once you're clear of frost, you can seperate them and plant outside.
Bok choy is best direct sow in spring or fall. But fall (july/august) is preferred.
The ideal temperature for bok choy is between 50 and 72.
hope this helps