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Pollination Problems

Pollination Problems

Posted by Seeds from Italy on 28th Jun 2021

A male squash flower produces ample pollen; it just needs a bee to carry it to a female flower for pollination to occur.

Every summer, we hear from a few people who say their squash, cucumber, melon, or pumpkin plants are flowering but not setting fruit. Or that the fruits drop off, or never fill out properly. These situations are normal, and easily remedied. The most likely cause is pollination failure, although growing conditions may also play a part.

Squash, cucumbers, melons, pumpkins and gourds all belong to the Cucurbitaceae family, commonly called the cucurbits. Nearly all cucurbits produce both female flowers and male flowers on the same plant. The female flower has a little fruit attached below the flower, shown at top in the photo; the male flower has only a stem. To get fruits, you need to have both male and female flowers open at the same time. You also need to have a pollinator such as a bee buzzing around the flowers and moving pollen from the male flowers into the female flowers. Cucurbit blossoms are open for less than a day, so the timing has to be perfect.

In the situation where you have flowers but no fruit, the solution is to just wait. Many varieties start blooming with all male flowers. Obviously, with no female flowers there will be no fruits. The male flowers will open, close and fall off. As the plant matures, it will produce a balance of male and female flowers that open at the same time. That’s when pollination happens, and if you have bees in your garden, you will soon see plants setting fruit. Flowers that are not properly pollinated will fall off, or have fruits that start to develop but never fill out.

However, you may not have pollinators in the garden on that special morning when male and female flowers are both open. A global decline in pollinators, especially honeybees, has been caused by invasive pests and disease such as mites and pathogens, pesticides, loss of habitat, and climate change. The decline in pollinators is cause for alarm because 75 percent of the world’s food crops depend on pollination — including nearly all the cucurbits.

In our own gardens, though, we can address a lack of pollinators by hand pollinating our cucurbits. Go into the garden in the morning armed with an artist’s or child’s paintbrush. Find a male flower and sweep up some of the pollen grains from the anther with your brush, then deposit them in the female flower on the stigma, the sticky knob in the middle where fertilization occurs. Put as much pollen as you can on the female flowers.

If, after hand pollinating your cucurbits, you still have fruits falling off, the problem could be water or temperature. Be sure you are giving the plants ample water. Very high or low temperatures or high humidity could also be the cause of failed pollination, but there’s not much you can do about that except wait for better conditions.