I would say that it was the result of improper pollination.
After a few days it will emit a rotting odour so you might as well remove it now.
A healthy newly developing pumpkin would be a lime green colour with a slight sheen on the outer skin.
Although pumpkins can be pollinated by other cucurbits and by itself, it is always better to grow two pumpkin plants in close proximity for pollination purposes.
You can also pollinate an open female flower by hand instead of waiting for insects or the wind to do it for you. Just cut off an open male flower, remove the petals to expose the pollen laden stamen and touch it into the female's pistil. Cover the entire surface of the pistil to guarantee proper pollination. Do this at about 10-11am before the maximum temperature is reached during the day.
If you intend to save seed from the pumpkin then tie the female flower closed after hand pollination to prevent cross pollination from visiting insects.
That’s very interesting, thanks for the information. It was the first flower on both plants so could explain a lot. I think I might have been too late to sow the seeds this year!
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After a few days it will emit a rotting odour so you might as well remove it now.
A healthy newly developing pumpkin would be a lime green colour with a slight sheen on the outer skin.
Although pumpkins can be pollinated by other cucurbits and by itself, it is always better to grow two pumpkin plants in close proximity for pollination purposes.
You can also pollinate an open female flower by hand instead of waiting for insects or the wind to do it for you. Just cut off an open male flower, remove the petals to expose the pollen laden stamen and touch it into the female's pistil. Cover the entire surface of the pistil to guarantee proper pollination. Do this at about 10-11am before the maximum temperature is reached during the day.
If you intend to save seed from the pumpkin then tie the female flower closed after hand pollination to prevent cross pollination from visiting insects.