Q. I have blooms on my cucumber plants, but they dry up and fall off without forming fruit. What's wrong? — A.G., via e-mail
A. There are three possibilities. All vining crops are monoecious, which means they have male flowers (staminate) and female flowers (pistillate) borne separately on the same plant.
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.