I'm really confused. I've always just built the farm on the wheat because I thought, 'hey, bonus wheat, got to be good for something'.
Now I'm in a game with a city producing 8 food per turn.
I have my builder build a farm on a wheat tile and hit the turn button.
Still.... 8 food per turn. So what's the point of building farms on wheat fields if it doesn't change your food production?
Ah, I see. Building the farm makes the tile a 'three food' tile, but ONLY IF YOU WORK IT. I only have two workers free (and one in the capital) and both the other plots I can select also have 'three food'. So I'm going from a '3 food' tile to a '3 food' tile.
But then what's the point of using your builder to build farms early in the game if you only get results if you can work that tile?