Why do my pumpkin flowers rotted and the fruits did not form. Only one pumpkin grew bigger, the rest fruits did not.
Thank you for contacting the Toronto Master Gardeners.
Although pollination problems are common in the Cucurbit family (e.g. cucumber, squash or zucchini), the solution is to help out personally.
Hand pollination is best done in the morning when the male and female flowers open. It can be done using either a q-tip or paintbrush, or with a male flower from which you have removed the petals to expose the anther. With a q-tip or paintbrush, touch it gently to the anther to pick up lots of pollen, then gently touch all parts of the female stigma, the top and all sides, to transfer the pollen. With the male flower, touch the anther gently to all parts of the stigma.
There is an additional timing consideration. Although we cannot control when the rain falls, waiting to water until after the pollination has occurred is an important factor to its success.
If you wish to review hand pollination details further, the following link is helpful:
Pollinating squash, cucumbers & pumpkins
Good luck with your gardening.
July 26, 2021