Not necessarily true all the time, Trill. My compost-origin pumpkin vines have finally started getting their girl flowers on, I think I'm gonna be eatin punkins soon! Turns out the trick was using a fertiliser with a different NPK balance.

BUT if you want to be sure, you could try growing them from seeds from organic pumpkin, or you could send away for some heritage pumpkin seeds, there are all sorts of amazing pumpkins out there. Jap and butternut and qld blue are pretty boring really