Assuming they were planted correctly and thinned properly the round purple top half or more of the root will show above ground, above the soil level. Using your fingers you can easily trace around it loosening the soil and determine the diameter of the root ball itself. When they are the size you want, harvest them, usually 2-3" in diameter or they will turn woody.

Also, depending on the variety you planted and when - you don't indicate your gardening zone so I can't help with that - the DTM on the pakage will give you a general idea as to when they will be ready for harvest. Average is 30-60 days after sowing.

Turnips are a cold weather crop so a fall to winter crop down here so they wouldn't even be planted yet or I'd post a pic for you to show what I mean. I linked some pics of them growing from Google so you can check them out.

Dave

Here is a link that might be useful: pics of turnips growing

I didn't realize how similar turnips are when growing to that of radishes - similar leaves too.

Nancy

Could you tell me if turnips can grow back from the winter before last, if they were not harvested? It appears that I have them throughout my garden even after tilling the garden really good.

The turnips will go to seed; they are biennials, like all root crops.

And are they definitely turnips? We had someone once before convinced they an infestation of rogue turnips and it turned out to be something else. A picture would settle it.