zucchini: lack of pollen


I have take to hand pollenating our zucchini for the past couple years. For some reason, the bees in our area don’t seem to know how to pollenate zucchini (when they know how to pollenate my other vegetable plants. This year I noticed something very odd …the male zucchini blossoms are lacking pollen. They weren’t too back for pollen in the spring, but now (starting towards end of July), the male blossoms are ‘dry’ …no yellow powder. At first I thought maybe earwigs were eating the pollen before I got to the flower, so I started to open the blossom before it totally opened up to insects …totally empty of pollen. Any ideas as to what causes ‘sterile’ male blossoms? I tried to send a photo, but it will not download onto the ‘attach a picture’ section. If I could have an email address, I could send it via email.

I am not a resident of Toronto, but from Waterloo Region. However, one of our business offices is in Toronto (containing Toronto residents), and we are into landscaping/gardening/plants in a big way. I have asked some horticulturalists already explaining my dilemma and they have no answers for me. Are you able to help me out?


Thank you for contacting the Toronto Master Gardeners with your very interesting question.

While researching this question I did find a number of gardeners with similar issues.  The one likely explanation  is temperature which can be a factor and affect pollen production. Apparently, cool or high temperatures, shade and insufficient moisture often results in pollen that does not behave normally. The days that you observed no pollen on the male flowers did they coincide with high temperature days? We did see temperature fluctuations near the end of July with some very cool evenings.

The University of California has an excellent article, Fruit Set Problems in Squash, Melons, and Cucumbers in Home Gardens . You may also find the article Incomplete Pollination of interest.

Here’s to a bountiful harvest.