One plant can produce
One plant can produce pumpkins. They can self-pollinate. To ensure pollination, we would suggest you help them pollinate by hand. A male and female flower have to be ready to bloom and open on the same morning. (The female has a little round ball of flesh at the base, all stigma, no pollen. The male has a straight stalk and a flower with all pollen.) Pick an opened male flower, take off the petals to expose the pollen, and dab it into the stigma of the female flower. That's it!