I have two different species of cucumber plants that have been growing well and have harvested five large cucumbers so far. Recently, all the small, 2-inch cucumbers that had just begun to develop turned yellow, shriveled and fell off—more than 10 of them! The plants are still growing well and the larger cucumbers continue to grow well. Why did these little cucumber buds yellow and die?
Cucumber plants have both male and female flowers. On most cucumber plants, the female flowers require pollination from the male flowers to produce cucumbers.
At first glance, it is hard to distinguish between the male and female flowers on the plant as they both appear as large, yellow flowers. On closer inspection, the female flowers appear to have an immature cucumber connected to the base of the flower. Once pollinated, the immature cucumber at the base of the female flower will grow into a large cucumber. If it is not pollinated, the immature cucumber will yellow and drop off. I believe this is what is happening to your cucumber plants. The best solution is to hand-pollinate the cucumbers. Using a small artist’s brush, you can remove pollen from the male flowers and brush it into the female flowers. Another option is to remove a male flower, carefully pull off the pedals and then physically touch the male flower’s anther to the stigma in the center of the female flower to pollinate it.
Cucumbers are not always the first choice for pollinating insects, so hand-pollination may be necessary to produce the desired yield. The same techniques for hand-pollinating cucumbers can also be used to pollinate squash and melons.