When the first flowers appear on zucchini plants, gardeners get excited about the zucchini harvest to follow. If flowers start falling off the plant, however, this may be a good thing or a bad thing. Understanding the difference between male and female flowers, and the role they play in squash production, is important in determining when to intervene and when to sit back and watch your squash develop.
Zucchini Flower Botany
Zucchini blossoms are big, yellow flowers that some gardeners pick to eat raw, stuff and cook, or batter and fry when they first open. The female flowers have an immature fruit at the base of the bloom, but just a thin stalk holds the male flowers aloft.
Making zucchini involves fertilization of the female blooms with pollen from the male blooms so that the immature fruit begins to grow. The flowers fall off as they shrivel with age, whether or not pollination occurs.
Often the first flowers fall off before pollination because the plant must have viable male and female flowers open at the same time and pollinators to carry the pollen from male to female flower.
Thus, the first flower or two of the season may fall off and no fruits form for no other reason than that both male and female flowers weren't present. It is common for male flowers to appear on the plants before female flowers. These flowers will fall off and there will be no sign of fruit. Unpollinated female flowers will fall off with the tiny fruit attached.
Once there are plenty of flowers open, but still no fruit, lack of pollination may be the reason the blooms fall off. Zucchini pollen is heavy and sticky, requiring insects to move it rather than wind. Bees are the most reliable pollinators, and if they are in short supply, you may need to hand pollinate. Picking a male blossom and rubbing the sticky pollen on stamens on the center, or pistil, of female blossoms, or taking a small brush and transferring pollen from male to female flowers may do the trick.
Sometimes you have male and female flowers, as well as pollination, but conditions aren't right for fruit to develop; flowers continue to fall off without fruit production. Some factors are under your control. The University of Montana Extension, for example, cautions against using too much nitrogen fertilizer, which may reduce fruit set. Extreme temperatures are another potential problem. Although you can be sure you don't set out plants too early, you don't have much control over very hot or cold weather that may interfere with fruiting, notes the Purdue Plant and Pest Diagnostic Laboratory's Rosie Lerner.
- University of Illinois Extension: Summer Squash
- University of California Cooperative Extension: Tulare/Kings Counties; Growing Zucchini: Not Always Easy to get Fruit; Hunter Johnson Jr.
- Montana State University Extension; How Come My Zucchini Plants Produce Lots of Flowers but Few Fruit?; July 2005
- Purdue Plant & Pest Diagnostic Laboratory; Pollinating Squash by Hand; Rosie Lerner