Most gardeners don’t worry much about how their vegetables get pollinated. For one thing, almost all of the popular vegetables people grow do just fine without any help from the gardener. But squashes can sometime be an exception to that. They depend on bees and other pollinators to do the job and without that happening, you’re not likely to get edible fruit. We have plenty of bees around our place, but they don’t always find the squash plants early in the season, so I step in and do the job myself. It’s easy to do if you know how! If you’re having problems getting your squash to set on, you might consider hand pollinating too. Today I want to show you how I go about it, but first we need to consider a bit of botany.
There are four species of squash commonly planted in home gardens. Some can cross pollinate with each other, but it’s best to stay within the same species for reliable results. Cucurbita pepo species includes most of the summer squash varieties like zucchini, yellow squash and pattypan plus winter types like acorn, delicata and spaghetti squash. Cucurbita moschata includes the butternuts, cheese pumpkins, neck pumpkins and tromboncino types. Cucurbita maxima includes kabocha, buttercup, hubbard and most pumpkins. Cucurbita argyrosperma is the species for cushaws. I pollinate moschatas with moschatas, pepos with pepos, and so on.
Vegetables like beans, peppers and tomatoes have ‘perfect’ flowers, with the male and female parts present in the same flower. Members of the squash family though have ‘imperfect’ flowers, which is to say some flowers are male and some are female. The female ones are what become the squashes, while the male ones supply the pollen. The two types of flowers are pretty easy to distinguish from each other once you know what to look for. There are a few varieties of squash that are parthenocarpic and don’t need pollination, but most all need to be pollinated to get good fruit set.
The male blossoms are on long thin stems, and the center of each open bloom has a pollen covered anther. The pollen sometimes begins falling off inside the blossom after it opens in the morning, and the bloom only remains open for a few hours before closing up. In the below photo I have torn away part of the flower to show the anther in the center of the bloom.
The female blossoms have an enlarged ovary just behind the bloom, which looks like a baby squash. That is the part that will develop into the mature squash. It’s easy to spot on this yellow squash because of the color.
On a green zucchini the ovary is green, and looks much thicker than the stem on the male blossom. If you look closely you can even see it has flecks like the bigger one next to it that was pollinated a couple of days ago.
The center of the female blossom contains the stigma, which will receive the pollen. In the below photo, ants have made their way into the bloom before I could get to it. There’s no sign they are hurting anything though so I don’t worry about them.
Since the blossoms open early in the morning, and close later in the day, I try and do the hand pollination early each morning. To pollinate the squash, I first find a male blossom that’s opened up. There are usually more of them than the female blossoms, so it’s not hard to do most of the time. I pluck or cut the blossom stem from the plant, then I carefully strip away the petals from all around the flower. This makes it easier to get the pollen from the anther on the stigma.
Once the petals are removed, you find a female blossom that needs pollinating and use the male blossom like a brush to gently “paint” the pollen onto the stigma. There’s plenty of pollen on one male bloom to pollinate at least one if not two female blossoms. Try and get some of the pollen all around the stigma. You’ll know if it worked in a day or two when the ovary starts to grow and develop into a squash. And that’s all there is to it!
For more information on hand pollinating squash, check out these sources:
Hand Pollinating Squash – Texas A&M University
Hand Pollination of Squash and Pumpkins – Missouri Botanical Garden
Hand Pollination of Squash and Corn in Small Gardens – University of Florida
If you are trying to save seed from your squashes, you need to do things a bit differently. For a good reference book I highly recommend reading Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners by Suzanne Ashworth. The book contains a wealth of information for saving all kinds of vegetable seeds, plus a few herbs like basil and parsley. Information is also available at the Seed Savers Exchange – Hand Pollination:Squash.