Why are my cucumber plants not producing cucumbers?
Cucumber, squash, and melon plants often bear many male flowers before female flowers appear. Examine the plants to determine whether female flowers are present. You can identify a female flower by the tiny cucumber at the base. Male flowers lack these. Click here to see a photo showing female and male cucumber flowers. If female flowers aren't present yet, the plants may be too immature to bear fruit. If the vines are healthy and growing in full sun, female flowers should appear in due time.
If fruit is not developing even though female flowers are present, the cause may be lack of pollination. Anything that interferes with pollination of the female flowers reduces fruit-set and yield. Factors that affect pollination include cold temperatures and rainy weather, which hamper bee activity, and improper use of insecticides that kill bees. If you think lack of pollination is the problem, try pollinating by hand. Locate the male blossoms. Break off several from the plant, and peel back their petals. Note the pollen on the insides of the blossoms. Gently push the pollen into the female blossoms with a paint brush, a feather, or the male blossom itself. This action should ensure a good crop.
Bob Minnesota Master Gardener