Why My Cucumbers & Zucchini Have Only Male Flowers

Zucchini blooms open before sunrise and close by noon.

Zucchini blooms open before sunrise and close by noon.

Cucumbers (Cucumis sativus) and zucchini (Cucurbita pepo) thrive in full sun in fertile, well-drained soil. Under ideal conditions, these garden annuals produce a flush of blooms approximately two weeks before the first fruits begin to form. Both produce male and female blooms on the same plant, but the male and female blooms do not appear at the same time. This often leads new gardeners to worry that all the blooms are male or that their cucumber and zucchini plants will not produce fruit.

Early Season Male Blooms

The male blooms on cucumber and zucchini plants serve two purposes. Their first job is to open and attract bees to the garden. This occurs approximately 10 days before the first female blooms appear. Male blooms are held above the vines via a slender stem. You should observe bee activity in and around your garden patch, but you will find few, if any, female blooms at this time. Because cucumber and zucchini plants rely on bees for pollination, a lot of male blooms and bustling bee activity is a positive sign and ensures good pollination -- the male blooms' second job -- when the time comes.

First Female Blooms Appear

By the time the first female blooms appear, bees have been buzzing through your garden patch for a week or more, and you can thank the male blooms for that. Female blooms have a tiny swollen ovary at the base of the bloom that looks like a miniature cucumber or zucchini. Without the flush of male blooms to attract bees, the female blooms might suffer from lack of pollination. The arrival of female blooms means your cucumber and zucchini plants are ready to produce fruit. You should now see both male and female blooms on your plants.

Abuzz With Bees

Male blooms produce pollen, the yellow-orange powder that covers the anther inside the bloom. They also produce sweet nectar to attract bees. When the bees visit the male bloom to drink the nectar, the pollen sticks to their hairy bodies. The bees carry the pollen with them as they visit the female blooms. When pollen rubs off the bees and sticks to the sticky stigma in the center of the female bloom, pollination soon occurs.

When Pollination Occurs

Once deposited in the female blooms, the pollen works its way down a tiny tube that connects the stigma to the ovary to pollinate the flower. The swollen ovary at the base of the female bloom then begins to grow into a new fruit. If the female flower is not pollinated, the swollen ovary shrivels and dies, and the bloom falls from the vine.

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