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Squash Pollination

By Melissa Kruse-Peeples, NS/S Conservation Program Manager. Published July 25, 2014.

One of the most common gardening problems from those growing squash, cucumbers, or watermelons is the abundance of baby fruits, but none that grow to full size. The baby fruits shrivel and wither away. The most common reason for this is that the fruits were not pollinated. In this blog post we share information about how cucurbits are pollinated and provide instructions for hand pollinating squash that can be applied to other species in this plant family.

Fruits of the Cucurbitaceae family, or cucurbits, require pollen from male flowers to reach the female flowers to fertilize the fruit. Cucurbits include all squash varieties like zucchini or pumpkins (Cucurbita pepo) and butternut squash (Cucurbita moschata) as well as cucumbers (Cucumis sativus), watermelons (Citrullus lanatus), melons (Cucumis melo), and gourds (Lagenaria siceraria).

The observation of “baby fruits” is more appropriately described as the presence of unfertilized ovaries. Bees are primarily responsible for the movement of male pollen to female flowers so if you lack bees, then you will lack adult fruit. The best advice to produce fertilized fruit is to attract a healthy population of pollinators to your garden by planting flowers and by using organic gardening methods. Particularly in some urban areas, bees can be hard to come by but there are hundreds of native bee species Arizona and we can all play a role in preserving these tiny creatures essential for healthy ecosystems. But if your local bees are playing hide and seek with your garden crops you can also practice hand pollination to produce fertilized fruits.

Below are instructions for hand pollinating squash. Similar procedures can be used for cucumbers, melons, and watermelons but the smaller size of the flowers requires delicate hands. Q-tips or small paintbrushes work well. Complete your hand-pollination activities in the morning when the pollen on the male flower is most viable. The pollen will have detached and fallen to the bottom of the flower making it harder to recover as it becomes warmer. Use several male flowers per female flower to increase the chances that the pollination will “take” and set fruit.

The male flowers have the stamens and the female flowers contain the pistils, whereas in self-pollinating plants like tomatoes or beans the stamens and pistils are contained within the same flower. Because they contain different reproductive parts, male and female flowers are easy to distinguish by examining the interior of the flower. Female flowers will have an ovary, or a small fruit developing at the base.

Female flowers can be fertilized by pollen from male flowers from the same plant as well as from the male flowers of other plants of the same species. Therefore, if you grow more than one variety of the same species in your garden, for example two different types of cucumbers, there is a high probability that cross-pollination will occur. This usually does not have any influence on the first generation of fruits produced and what you eat for dinner but it will influence the seeds saved from those fruits. Practicing hand pollination is necessary if you wish to grow more than one variety of a curcubit species and save seeds (see step 3 below). Otherwise it is likely that the seeds saved will produce off-type fruit that will not resemble the parent variety. Even if you only have one variety growing it is possibly that your neighbor’s varieties will cross-pollinate with your garden. Therefore if you are serious about saving true-to-type seeds you should practice hand pollination. Mark your hand-pollinated fruits with flagging tape or a piece of string to remember which were hand pollinated.

Click to enlarge or download a printable version of this handout here.


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