Like other cucurbits, zucchini and cucumbers are monoecious plants. Each plant produces both male and female flowers. When there are no female flowers on your zucchini, it may be that the first set of flowers are all male, or one of many other factors including light, temperature, genetics and stress.
Genetics and Timing
Some cucumber and zucchini plants have a natural tendency for producing more of one sex than another. On most of the plants, the male flowers tend to appear first and then female flowers. Some zucchini plants have been bred to produce more male flowers in order to supply the demand of courgette. Others have been bred for greater fruit production and since one male flower can pollinate several females, those varieties tend to produce just a few male flowers.
The Effect of Light on Flower Type
Both light intensity and length of day effect the ratio of male to female flowers on cucurbits. More male flowers are formed when the day length is long and the light intensity is high. If your plant is in full sun all day and producing only male flowers, you may want to provide light shade or plant it in a different location.
The Effect of Temperature
Cooler temperatures tend to favor female flowers. If you have had a hot summer, you may find an abundance of male flowers. Light afternoon shade will help reduce the effect of high temperatures.
Infrequent watering and over crowding will cause stress in your plants and may result in increased male flower production in your zucchini and cucumbers. Start with good, well-drained soil and plant it at the recommended spacing. Then water regularly to keep evenly moist.
- University of Illinois Extension; Pumpkins and More; Growing; Ron Wolford, et al. Pumpkins;Ron Wolford et al.;
- Michigan State University Extention; Integrated Pest Management Resources - Lack of Male Flower Formation in Squash; Mathieu Ngouajio; Aug. 19, 2009
- B's Cucumber Pages; Commercial Cucumber Production; B. Cohen; Sept. 5, 2009
- Photo Credit Hemera Technologies/Photos.com/Getty Images
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