[Hadakare]

As I intend growing a few pumpkin this year just wondering if it would be possible to grow a Square shaped one if it was grown in some sort of constricting frame device?

[LotuSeed]

Don't see why not, they do the same with watermelons in Japan.
http://kotaku.com/japan-has-more-than-just-square-watermelons-way-more-823476111

At the very least it'd be a cool experiment!

[ptarmigan]

I did it by accident.  Was growing a sprawling pumpkin on top of the compost heap - the type that has a number of smaller fruits - worked really well.  Found one that had started growing down the back trapped in between the pallets of 2 composts and came out flat on 2 sides.  Still tasty.

[mjg000]

And they certainly end up with a flat bottom if they are left on the ground!

[Beekissed]

It can be done!