My cucumbers are growing quite well and I have plenty of flowers on them. But as soon as the flowers are finished blooming, the little cucumber that forms in the back of the flower dies off and shrivels away. This is the first year this happened to me. I have been growing cucumbers for many years and never had a problem.
If the male flowers drop off, this is normal. If the female flowers are dropping off, this is due to lack of pollination.
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