Kansas Ag Connection - Vegetable Plants Not Always Setting Fruit

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Vegetable Plants Not Always Setting Fruit
Kansas Ag Connection - 07/30/2010

The rising number of U.S. gardeners growing vegetable crops may now be facing an array of strange problems, including plants that are blooming, but not setting any fruit.

"The reasons for lack of fruit set often vary by type of vegetable. But, one factor can cause this condition in several species at about the same time. It's a rookie's mistake - applying too much fertilizer," said Ward Upham, horticulturist with Kansas State University Research and Extension.

Up to a point, excess nitrogen inspires plants to focus on foliage, Upham explained. Lush top growth may outstrip the roots' abilities to supply nutrients and water. Other results can include a delay in flower production and/or a decrease in fruit set from the flowers that do appear.

Tomatoes - the nation's favorite homegrown veggie - are one of the plants that also can have weather-related problems. Tomato plants simply won't set fruit when nighttime temperatures are above 75 degrees, he said. Because their pollen output gets sparse when nights are cooler than 50 F, the plants normally won't set fruit then, either.

"Squashes, on the other hand, can have actual pollination problems - ones that gardeners may be able to do something about," Upham said.

In the "strange, but true" category, squash plants' early flowers are typically all males -- i.e., no fruit possible. As time passes, however, the flower production becomes more balanced between males and females. (The female flowers have a tiny "fruit" behind their blossom, where it attaches to the stem.)

"That's when you need pollinators flying around," the horticulturist said. "Unfortunately, bees have been having their own problems in recent years, and their numbers are down. No American can afford to be overusing or misapplying insecticides any more."

If bees aren't visiting, however, squash plants are fairly easy for gardeners to hand-pollinate. The process involves using a small artist's brush to transfer pollen from the anther of a male flower to the stigma of a female flower. Upham warned, however, that it also can require accepting the fact that "pollinating all possibilities may be a bigger job than any one gardener wants to handle. With squash, limits are okay."

For gardeners interesting in trying the process, he said, Extension horticulturists at the University of Florida have posted photos of the involved plant parts on the Web at http://edis.ifas.ufl.edu/hs398.