These crops depend on insects, such as bees, to transfer pollen from the male flowers to the female flowers. If this doesn't occur, the female blossom will fall off. The male flowers always fall off.
It's possible you don't have insects pollinating the blossoms. This is why insecticides should not be used on vining crops during the daylight hours after vines produce flowers. Also, when plants are flowering, never use an insecticidal dust. Apply a liquid formulation, late in the evening, when insects aren't present.
You can identify the female flowers. They have miniature immature fruits behind the petals that resemble mature fruit.
You can manually transfer the pollen from the male flowers to the female flowers, but this is tedious.
You might also have a cultivar that is “gynoecious.” It was bred to produce only female flowers. However, you must have at least one monoecious plant to produce male flowers and pollen.
Normally the monoecious plant's seed will be dyed a color to distinguish it from the gynoecious plants' seeds in a seed packet. Be sure to plant it to get a pollen-producing plant If you don't, the female plants' flowers will dry up and fall off.
The last week of August is the time to:♦Cut the blooms of echinops (globe thistle) to use in dried floral arrangements for indoors this fall.
♦Begin to check apple trees for ripe fruit and pick it. Critters such as birds, chipmunks and squirrels will happily help you harvest the fruit, if you don't get there first.
♦Dig, divide and replant iris, bleeding heart, Oriental poppy and peonies (including tree peonies). Keep the new plantings watered during dry weather. Share some divisions with friends and neighbors.
♦Side-dress tomato plants with a last, light application of a high-nitrogen fertilizer material to encourage production of fruit for fall harvest.
♦Remove weeds from a new strawberry bed. Apply a fertilizer material to promote formation of flower buds for next season's crop. After applying, gently sweep stray granules off the leaves with a broom or wash them off with water.