Last year I tried to grow pumpkins and only got one sex of flower. Can pumpkins be successfully hand-pollinated? What are natural pollinators for pumpkins? We seem to have a shortage of bees, just lots of wasps.
Arapahoe County Colorado
A pumpkin plant has both male and female flowers. An excess of nitrogen can cause the plant to not reach maturity and produce flowers. (The male flowers are produces first, followed by the females about a week later.)
There are primarily two things that reduce fruit setting on pumpkins, lack of pollinators or extreme heat. Like tomato blossoms, pumpkins will not set fruit in extreme heat. It was pretty hot last year and that may have contributed to your problem.
At any rate, check out these two documents. They will give you more details and the first one describes how to hand pollinate a pumpkin. https://ag.purdue.edu/btny/ppdl/Pages/Pollinating-Tomatoes-and-Pumpkins-by-Hand.aspx