I remember my Dad grew a big 'un when I was small. The fire brigade had an inter-watch competition to see who could grow the biggest, smallest, best dressed, etc etc. We had a fairly big one that he grew in the greenhouse amongst the tomatoes, when we cut it off the plant we dressed it as a witch (as we didn't think it was that big), complete with the stem as the witches' warty nose (we used some black wool to make it hairy, and stuck googly eyes on it, and made a witches' hat).
Well, he wasn't popular at work cos it won both biggest and best dressed. The other pumpkins had been grown outside and were no bigger than a dinner plate - ours was roughly the size of a space hopper. Can't remember what he won, but it was a kids' party at the station, so it was probably some thing for us kids.
It was kept in a greenhouse and all of the other fruits on the plant were removed, so all the plant's energy went into producing the single big one. I think it got watered with the tomatoes, so it would have been fed at least once a week too.
This year I am trying to grow some halloween pumpkins for my little ones (the shop-bought pumpkin was a big hit with them last year), no greenhouse so I don't know how they'll fare - if spring ever arrives that is!