My Squash Plants Only Produce Male Flowers

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Squash plant with male flower. Photo: extension.unh.edu

Question: I think something is wrong with my squash plants. They produce only male flowers. 

C. Carmichael

Answer: Just be patient: the female flowers will come.

Squash such as zucchinis and pumpkins, as well as most other cucurbits (cucumbers, melons, watermelons, etc.), produce unisexual flowers—separate male and female flowers—on the same plant. 

Male flower on the left, female, with its swollen ovary, on the right. Photo: http://www.missouribotanicalgarden.org

The two can be readily told apart by ovary in the form of the future fruit (round, long, crookneck, etc.) found at the base of female flowers. Only female flowers. The males have no ovary and produce, of course, no fruit, but are vital as they provide the pollen needed by the female flowers to produce fruit.

Ma Nature produces male flowers first to start to attract pollinators. Producing male flowers requires little energy and they are produced abundantly. Each lasts but a day, but new ones replace them. So, after a few weeks of male-only flowers, pollinating insects such as bees will hopefully have become accustomed to visiting the flowers daily to pick up pollen and nectar. That way, when the first female flowers appear, there’ll be bees ready to pollinate them. 

So … just wait. The female flowers are on their way!

In the Absence of Pollinators

But what if you’re not seeing bees visiting your squash flowers? First, you do have to look in the morning: squash flowers are pretty much morning bloomers. And adverse weather—heavy rain, extreme heat, unusual cold, etc.—can keep bees away. Also, don’t water on mornings when the plant has female flowers … or if you do water, water only the soil, not the blooms. With that female flower only opening for one day, you do not want to discourage pollinators on that one occasion! 

These improperly pollinated fruits were aborted. Photo: J. Allen, uconnladybug.wordpress.com

It takes up to 12 bee visits to properly pollinate a squash flower. If bees are not visiting regularly, you have a problem, as improperly pollinated fruits will abort and drop off.

Hand pollination may be necessary. Photo: sendjoelletter

That’s why hand pollination is useful and may even be necessary. In fact, many gardeners find they obtain earlier and more numerous fruits when they hand pollinate, largely because that way, more pollen is applied and therefore fewer fruits abort. Read Be Like a Bee and Pollinate Your Curcubits to learn how to hand pollinate your squash flowers. 

Be Like a Bee and Pollinate your Cucurbits

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The female flower has an ovary at its base.

You’ve probably noticed have noticed that squash (zucchinis, pumpkins, gourds, etc.), cucumbers, melons and other cucurbits have both female flowers and male flowers. Female flowers are few in number, but easy to see as they already bear an ovary at the base that looks like a miniature version the fruit that will form. So on a pumpkin, it will be rounded, on a cucumber, long and thin, on a patty pan squash, scallop-shaped, etc. In the center of the female flower, there’ll be a crown-shaped stigma.

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The male flower has no ovary at the base.

Male flowers have no ovary at their base. They are numerous and far outnumber the females. If you look inside, you’ll see they have a “ball” of yellow pollen on a central stamen, absent, of course, in the female. To produce a fruit, the male pollen must somehow be transferred to the stigma of a female flower.

And this transfer has to happen quickly, the same day the flower opens, because each cucurbit flower lasts only one day.

Sometimes, however, pollinating insects are absent when a female flower is in bloom. This can happen if it’s raining that day or if the weather is unusually hot or cold, all conditions that discourage pollinating insects. Or maybe there are simply very few bees or other pollinators that visit your garden. And it takes up to 12 visits from a pollen-laden bee to completely fertilize the female flower.

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How to apply pollen from a male flower to the female flower.

If so, you need play the role of a bee for the day. Harvest a male flower, remove its petals to better see what you are doing, then use it as if it were a brush, touching the rounded end of the stamen, covered in yellow pollen, to the crown-shaped stigma in the center of the female flower. Alternatively, take an artist’s brush or a cotton swab, touch it to a male flower to coat it with yellow pollen, then “paint” the pollen onto the stigma of the female.

In both cases, you’ll be pollinating the female flower, ensuring its fecundation … and resulting in a beautiful fruit a few weeks later!