Hand Pollinating Squash

Jay White, Horticulture Graduate Student, Texas A&M University

Squash vine borers are just horrible in my part of Texas. Because of this, it is almost impossible to get a great crop of any of the standard summer squash varieties grown in our area (yellow crookneck, zucchini or patty pan).

Squash Vine Borer Moth
Squash Vine Borer Moth in Patty Leander's garden. Photo by Bruce Leander

As I talk to people, I get more questions about how to control this destructive little pest than any other. Quite frankly, if you are an organic grower, there is not much you can do to beat the borer besides growing your plants under row cover (if you are not organic, Sevin dust does a fairly decent job of keeping borers away, but it needs to be applied every four or five days). If you properly grow under row cover you will definitely stop the vine borer. However, you will also prevent bees and other pollinators from reaching the plants. Because of this, if you want any fruit, you will be forced to pollinate your plants by hand. Luckily, hand pollination of squash plants is very easy to do.

Female acorn squash flower on trellis
Female acorn squash on trellis

Flower Identification - Hand pollination of squash blossoms requires no special skills or tools. All you have to do is be able to identify male and female flowers. On squash, this is very easy to do. Female flowers will always have a tiny fruit under the flower.

Closeup of female stigma
Closeup of female stigma
Back of female flower
Back of female flower

Male flowers grow on a long narrow stem. You can also tell the two apart by looking at the reproductive organs found in the center of the flower. The female flowers contain the stigma. The stigma generally looks like a flower in its own right. It has several "bumpy structures" that cluster around a central opening. Anthers (male parts) look a lot like the thing my wife uses to apply eye shadow.

front of male flower'
Front of male flower
back of male flower
Back of male flower

Hand Pollination - When growing under row cover you will need to pollinate as soon as the flowers begin to open. When this happens, roll back your cover and find a male flower. Cut it off where the flower stem meets the main stem of the plant. Next, gently remove all of the petals from the flower. Once the petals are gone you are left with a stem and exposed anther that is about 4" to 6" long.

anther ready for pollination use
Anther ready for pollination use

Now find a female flower and use your stem and anther to "paint" the stigma in the center of the female flower. Gently rub the anther over the stigma a few times. Then go on to the next female flower. Each anther can be used to pollinate approximately five flowers.

'Painting' the stigma
"Painting" the stigma

Caution - A fellow gardener once told me that they were crushed to find a vine borer trapped under their row cover after they had hand pollinated. If this happens to you don't worry. While it is best if you can keep your squash plant bug free for its entire life, a mature squash plant can usually "outgrow" a worms infestation if the eggs are not laid until after pollination occurs. Because of this, many gardeners that grow under cover often remove the cover completely when the pollination is done.

If you want to keep the cover on throughout the life cycle, work with a buddy and pollinate in the late afternoon (borers are most active before noon). Roll back the cover and quickly harvest several male flowers. Put the cover back in place as you strip the petals from the male flowers. When you have all of the anthers exposed quickly pull the cover back and pollinate all of the female flowers at one time, then quickly put the cover back in place and anchor the sides to the soil.

Squash being grown under cover in Patty Leander's garden
Squash being grown under cover in Patty Leander's garden. Photo by Bruce Leander

This method of hand pollination is a great tool to master and you can use it for all of your cucurbits. If you do it right, I am convinced it will increase your yields This fall I grew acorn squash. Since we have been short on bees, I did a small experiment. I hand pollinated half of my vines and let nature pollinate the other half. I got almost a 100% yield from the flowers I pollinated. Mother Nature was only successful about half the time.

This article originally appeared in the blog "The Masters of Horticulture" by Jay White

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