Answer: I can tell you what has happened, but I'm not sure I can tell you why. Pumpkins have both male and female flowers and pollen must be transferred from the male to the female flower. This is usually something the bees and wasps do, but if for some reason there is not a healthy population of flying insects in your garden, pollination will not take place. You can help things along (although it is a little late in the season) by removing a male blossom and rubbing it inside a female blossom to transfer pollen. Male flowers are attached by a slender stem; female flowers have a slight swelling directly behind the flower petals. Give this process a try and maybe you'll get at least a tiny pumpkin for your efforts.
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