I checked the turnip on Thursday, it was 2 inches or so in diameter. Checked it again Saturday, it's 4 inches, argh. There it is, all washed up, ready to go in the house.
That is a 15oz can next to it for size comparison. It's the only turnip to reach maturity, the others were either bug food or didn't grow. I will try some more in a few months, maybe the bugs will let me harvest a few.