Hand-Pollination of Squash

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Hand-Pollination of Squash

Learn how to pollinate squash by hand with this technique.

By Micaela Colley & Jared Zystro

The Seed Garden (Seed Savers Exchange, 2015) by Micaela Colley & Jared Zystro and edited by Lee Buttala & Shanyn Siegel brings together decades of research and hands-on experience to teach both novice gardeners and seasoned horticulturists how to save the seeds of their favorite vegetable varieties.

You can purchase this book from the MOTHER EARTH NEWS store: The Seed Garden.

The four species of squash normally grown as garden vegetables—Cucurbita argyrosperma, Cucurbita maxima, Cucurbita moschata, and Cucurbita pepo—can be hand-pollinated when being grown for seed. All four species share the same floral anatomy and respond to the same pro­cess of hand-pollination.

Although squash plants bloom continuously over the course of the growing season, each flower opens for just one day, and hand-pollination requires some planning and attention to timing. The process of hand-pollinating a squash flower occurs on two consecutive days. The process begins in the late afternoon of the first day, when flowers that will open the following day are identified and secured shut, and is completed the next morning, when the flowers are pollinated manually.

Squash plants are monoecious, and all male and female flowers that will be used in hand-pollination need to be secured shut before they open to prevent errant pollen from contami­nating either blossom. A female flower is easily identified by its visible ovary, which resembles a small squash and is located just below the petals and sepals; flowers lacking ovaries are male.

Identifying flowers that are about to open takes some practice but is relatively straightforward. When in bud, squash blossoms are greenish yellow or creamy yellow in color. On the day before they open, the fused flower petals will begin to split apart at the tip, and a small seam of bright yellow will typically be visible on the inside of the petals.

The male flowers, which provide the pollen, should be secured shut with flagging ribbon, tape, clothespins, or any other material that will pre­vent the petals from opening and allowing insects access to the reproductive organs. Inserting a flag in the ground next to each sealed flower allows the prepped flowers to be easily found the next morning amid the foliage. Follow the same pro­cess when sealing the female flowers, making sure to leave enough of each flower’s petals intact so that the blossoms can be secured closed again after hand-pollinating.

The following morning, hand-pollination is carried out at the time of day when squash flow­ers are normally open. They usually open just after dawn and remain open until early afternoon, though the exact timing and duration is influ­enced by environmental conditions. The male squash flower, typically borne on a long pedun­cle (stalk), should be picked and brought to the female flower. Remove the male flower’s petals entirely, leaving the anthers and pollen exposed upon the end of the peduncle. Moving quickly, carefully open the female flower—the goal is to complete the hand-pollination process before any bees intervene—and brush the pollen from the anthers onto the entire surface of the stigma. The pollen grains are large enough that they will be visible on the stigma after pollination. Close up the petals and tape the flower shut, ensuring that there are no openings that pollinating insects can get through. Re-sealing the female flower ensures that the seeds produced will have been fertilized through hand-pollination and not by insect pol­lination that could occur later on that same day, while the stigma is still receptive. Tie a weather-resistant marker to the stem of the hand-pollinated flower so the isolated fruit can be easily identified at harvest. The petals will likely shrivel and fall off after fertilization is complete.

Hand-pollination can be done using just one male flower for each female flower, but transfer­ring pollen from two or three male flowers to the receptive stigma of a female flower will effectively include more plants in the reproductive popula­tion. If possible, choose male flowers from separate plants than the one bearing the female blossom to help maintain genetic diversity.

It is a good idea to pollinate at least four times as many flowers as the number of fruits desired for seed collection, especially when first learning to hand-pollinate flowers.

In the afternoon, identify male and female flowers about to open. Secure male (above) and female flowers closed. Mark the location of sealed flowers.
The following morning, collect sealed male flowers from plants and locate
female flowers to be pollinated.
Working quickly, remove all petals from male flowers and unseal female blossom.
Still working quickly, brush pollen from anthers onto entire surface ofstigma. Pollen grains should be visible. Thoroughly seal pollinated female flowers. Mark hand-pollinated flowersso that the isolated fruits can be identified later.

For more on seed saving, see our Seed Saving Guide.

Reprinted with permission from The Seed Garden, by Micaela Colley & Jared Zystro, edited by Lee Buttala & Shanyn Siegel and published by Seed Savers Exchange, 2015. Buy this book from our store:The Seed Garden.