Tuesday’s Tips — Fruit Set Problems in Squash

Or we might have titled this post “Why Bees Are So Important.”

In January the press reported that scientists had noticed a significant decline in bumblebee populations in the U.S. — first it was the honeybees that were disappearing and now it’s bumblebees too. Scientists are not sure why just yet, but one thing they can agree on is that this is not good news because bumblebees pollinate about 15% of all crops in the field — blueberries, cranberries, raspberries, squash and watermelon; and in the hothouse — tomatoes, strawberries and peppers.

And it’s not just the many different variety of bees (honeybees, bumbles, carpenter bees, mason bees, metallic sweat bees, leaf-cutter bees, ground-nesting bees, and various localized native bees) that pollinate flowers. There are many other creatures that do this work like ants, beetles, moths, flies, birds, butterflies, wasps, bats, and even a few mammals that transport pollen as they make their rounds.

Which is kind of the long way round to the question of problems with fruit set in squash, melons and cucumbers. Several people have asked why the flowers on squash and cucumber plants have been falling off. There are several reasons.

The first thing you should know is you might not have a problem. Squash, melons and cucumbers belong to the cucurbit family and they all have a unique flowering habit. Each plant bears male and female blossoms. The female blossom has a miniature fruit (ovary) at the base of the flower. Male blossoms don’t have this swelling. The male flower’s only job is to provide pollen to fertilize the ovary in the female flower and they depend on bees to do this. If the pollen isn’t transported from male to female flower fruit set will never happen.

Early flowers tend to be mostly male and these will fall off with no sign of fruit set. Not to worry, this is normal. On certain hybrid varieties of summer squash the early flowers are mostly females that don’t get fertilized and they will drop as well.

When the plants start producing both male and female flowers at the same time things should start clicking — unless there are no bees around. Cucurbits have sticky pollen and need bees to transport it from male to female flower. If your garden doesn’t have enough bees to pollinate the female flowers you will not get fruit.

In the absence of bees the only option is to hand pollinate. Get a small artist brush and pick up the yellow pollen that you will find inside the male flowers. Take the pollen-coated brush and paint it onto the stigma in the female flower. It is important to do this to only flowers that have just opened as they are only receptive for a single day.

It would be so much easier to have bees do the work! Without them crops will fail, plants won’t thrive, and we will be hard pressed to find solutions to this growing problem.

How can you help? Rule number one is to NEVER use pesticides in your garden. No matter how careful you are you will almost always kill at least a few bees. Rule number two is to create a garden that will sustain bees and all the creatures that help us grow food and the other plants we love. You can find tips on creating bee-friendly gardens in this post and by clicking some of the links on our resources page.

One last note, though we always recommend lots of mulch for your garden beds be sure to leave a few small areas bare for ground-nesting bees. Mulching is thought to be one of main reasons that this type of bee population is diminishing.

Save the bees!