Fallout is some tricky stuff. The Bikini islands "looked" ok with trees and vegetation growing years after we blew them up but you wouldn't dare set foot on them without protection.
When I worked at the water dept. there was a manual that spoke of what to do after we got nuked. One part described taking a normal can of beans and placing it in an open field and setting off a nuke nearby (far enough not to vaporize it but close enough to get good blast of radiation). When you find the can of beans the next day it will be covered with dirt (fallout). The beans inside of the can will be perfectly safe to eat but if you get so much as a speck of the dirt inside of you, you're history.
I guess what I'm saying is that just because plants are growing there doesn't mean that it's not without danger.