You can leave some in the ground until the following year to collect seed at that point.I think my carrots don't look like garden porn pictures because I don't thin them the way you are supposed to. Last year I left some carrots in the ground for nearly 6 months. The tops were huge...bushy...at least 18" tall. When I finally got around to pulling them, the carrots were maybe 6 inches long at best and as fat as my thumb. Disappointing.... But they sure did taste good and the buns enjoyed the tops!