From Creatures Wikia
The pumpkin plant (made by Freya of the Creatures Jungle) is invisible for norns, grows in your greenhouse (or outside if you don´t have the greenhouse COB), and when it´s full-grown three little flowers will appear. They will mature into three pumpkins that are ready to be picked when they´re ripe.
When a norn eats a pumpkin it will receive:
And, if you place the pumpkin into the working oven cob (on top of the fire) it will change appearance. If you press it, it will turn into something nice to look at for the norns. When a norn watches a baked and activated pumpkin it will receive:
When all the pumpkins have been eaten, alternately baked, 3 new flowers will appear on the pumpkin plant.
If you want to get rid of a baked pumpkin; just drop it into the incubator. It will then disappear.