Extension Service Garden Hints

OSU vegetable breeder explains the secrets of squash and cucumber pollination

CORVALLIS, Ore. – The weather is hot enough for heat-loving squash and cucumber plants to start blossoming and setting fruit. Successful pollination and fruit set of garden cukes and squash depends on insect pollinators such as honeybees and native bees and also timing and location.

Most squashes and cucumbers have separate male and female flowers on the same plant, explained Jim Myers, vegetable breeder at Oregon State University. So, to produce fruit, pollen from male flowers must be transferred to the female flowers.

How do you tell a male from a female squash or cucumber blossom? The female blossoms have what looks like a tiny squash or cucumber below the flower. The tiny fruit is the ovary, full of eggs not yet fertilized via pollen from male flowers. Male blossoms have long-stalked stamens, each with pollen-filled anthers. Every pollen grain contains sperm nuclei, which fertilize the ovules in the female flowers.

Visiting bees and other types of insects provide the transfer of pollen from the male to the female blossoms. When visiting squash and cucumber flowers to collect nectar and pollen, bees carry and spread the male pollen from male anthers to female pistils. Each pollen grain grows a long tube down through the pistil, to the egg cells. The sperm nuclei migrate down the tube to the egg, where fertilization takes place. The product of the union of the egg and sperm is a tiny plant embryo, inside each seed. Surrounding the seeds, what we think typically think of as the squash or cucumber, is actually the plant ovary, which houses the embryos inside their protective seeds.

Don't worry if the earliest blooms on squash or cucumber plants fall off before they set any fruit. The male flowers of cucumbers and squash often bloom and wither before the female blossoms start appearing.

So be patient with squash and cucumber plants, advised Myers. Eventually, most will produce both male and female flowers. Once blossoms of both sexes are opening at the same time and there is still no fruit formation, there may be poor pollination.

Sometimes Mother Nature needs help, if you have a shortage of pollinators. Home gardeners can pollinate the flowers themselves. Use a small watercolor paintbrush and lightly transfer pollen from male flowers to the female flowers.

Past research in the OSU Department of Horticulture has shown that growing cilantro, yarrow, wild buckwheat, white sweet clover, tansy, sweet fennel, sweet alyssum, spearmint, Queen Anne's lace, hairy vetch, flowering buckwheat, crimson clover, cowpeas, common knotweed and caraway attract natural pollinators and other beneficial insects including natural predators.

Once fruit develops keep the plants well watered. Don't let cucumbers or summer squash get too big – they often get seedy, stringy or tough.

To learn more about growing cucumbers and squash, the OSU Extension Service offers the following publications online or via the U.S. mail.

“Grow Your Own Cucumbers” (EC 1226)

“Growing Your Own” – a practical guide to gardening in Oregon, featuring vegetable varieties, planting dates, insect control, soil preparation, and more...

“Vegetable Gardening in Oregon” (EC 871)

For printed copies, call 1-800-561-6719 to request a catalog.

By: Carol Savonen
Source: Jim Myers

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