Carol Bradford: Many pollinator visits needed to grow zucchini

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on September 21, 2012 at 10:02 AM, updated September 21, 2012 at 10:19 AM
THERE ARE some 400 species of native bees in New York. Some are large bumblebees, but most are tiny and can be hard to spot and even harder to identify. The pollen and nectar from late blooming flowers like asters help these vital insect pollinators to overwinter. One out of every three mouthfuls you eat is directly or indirectly dependent on pollinators, according to the USDA.

Courtesy Carol Bradford

Dear Carol: I have been a gardener for many years, both plants and vegetables. For the past two seasons the zucchini plants have not produced any fruit.

There is ample sunshine. I water, and bees seem to visit the flowers. We get beautiful flowers and then they fall off. What do you think? -- G.P., Baldwinsville.

Dear G.P.: When zucchini crops are good, they are very, very good. Some people have told me they had excellent yields this summer. Several things have to happen for the plants to produce fruit.

Vegetable gardens need full sun. This summer especially, extra water was needed because the weather was so dry. Inconsistent moisture levels in the soil will cause developing fruit to become misshapen or to fall off.

It's possible that a plant is too stressed by insect pests or diseases to produce a crop. There would be other symptoms in that case besides failure to yield.

Zucchini (and most plants in the squash family) have separate male and female flowers on the same plant. The female flowers have a tiny fruit at the base. The male flowers don't. Typically the plants make male flowers first, and then make female flowers later in the season. The male flowers always wilt and fall off.

The female flower will grow a zucchini if it is properly pollinated and the other conditions are met. Squash plants are pollinated by insects that move from flower to flower, transferring pollen from male flowers to female flowers.

If the weather is too wet, too hot or too cold, the insects may not fly. The pollen may also not be able to fertilize the ovules properly if it's too hot. That can also cause the fruit to develop abnormally or to fail to grow.

It takes many pollinator visits to grow a zucchini. Every seed is separately fertilized. So there have to be enough insects. Anything you do to encourage insect pollinators can help.

The Xerces Society for Invertebrate Conservation,, or (855) 232-6639, has resources and information on protecting pollinating insects and their habitat. Like all living creatures, insects need food, water, shelter and a place to rear their young. Given the decline in nonnative honeybee populations, there's been a focus on the role of native bees.

There are more than 400 species of native bees in New York State. Ninety percent of the species are solitary, not social, and do not live in colonies or hives. These bees are gentle and non aggressive.

Some bees are tiny and may not travel more than 500 feet. They need flowers for nectar and pollen all during the season. Region specific lists of flowers that bloom from earliest spring to late fall are available to help plan hedgerows, blocks and strip plantings in your garden that will bring more pollinators in.

Avoid using pesticides. They are worse for native bees than for honeybees and can harm native bees even when label directions are followed.


» Read more gardening advice from Carol T. Bradford