Hand Pollinating

Each spring, pollen grains are normally moved from flower to flower by honey bees, beetles, butterflies and moths, and wind. When the pollen arrives at another flower, fertilization can occur and fruit can grow. Except, sometimes, the pollen needs a little help. That’s where hand pollination comes in.

Hand pollination of two gourd blossoms (Wikipedia) CC BY-SA 2.0

Plants being grown indoors, or in areas without enough bees and other pollinators, cannot set fruit without mechanical pollination. Some crops, such as cucumber, melon, pumpkin and other squash, can be coaxed into producing far more fruit if hand pollination its used, due to the timing issues related to male and female flowers occurring at different times.

If you grow plants indoors, you will need to pollinate the flowers by hand to get fruit. Container plants that are at a distance from their fellows will also benefit from hand pollination. Loquats, kiwifruit, and mangos, in particular, often require hand pollination. [Due to heavy pesticide use in China, the lion's share of all their fruit crops are now pollinated by hand.]

Hand-pollination is not difficult, but it is tedious. To better understand how hand pollination works, let’s have a quick review of flower anatomy and the pollination process.

Flower anatomy

For a more detailed description, I urge you to read my posts on flowers and pollination. In the most basic terms, flowers can be male, female, or both, but not necessarily at the same time. Male flowers have a stamen and female flowers have a pistil. The stamen consists of a pollen-producing anther at the end of a filament. Pollen tends to be yellow and sticky. The female pistil, also known as a carpel, is usually found in the center of a flower and it consists of the sticky stigma, which captures pollen, the style, a tube that leads to the ovary, and the ovary itself. ​

Parts of a flower (LadyofHats) Public Domain

Pollination

As insects move around, collecting nectar and pollen for themselves, sticky pollen becomes attached to their legs and is carried from flower to flower. The pollen is captured by the stigma, enters the style, and moves toward the ovary, where fertilization occurs. If there are not enough pollinators, the pollen doesn’t get moved and we have no fruit. Unless you hand pollinate. By hand pollinating, you become the mechanism by which pollen is moved from the stamen of the male flower to the pistil of the female flower.


How to hand pollinate

There are two basic methods of hand pollination: removal of the anther, or transferring just the pollen. In most plants from the cucurbit family, the male anther is large and obvious. Without handling the part covered with pollen, simply snip off the anther, cut off or roll back the flower petals, and gently roll it around on the female pistil.

On plants with smaller flowers, such as cucumber, tomatoes, and melons, you can use a small, natural bristle painter’s brush or a cotton swab to transfer pollen from one plant to the other.

Timing is important

Male flowers tend to emerge before female flowers. Also, most flowers are only receptive to pollen for one day. Transfer pollen to freshly opened flowers, preferably in the morning. Do this every day until fruit starts to form.

Concerns about cross-pollination

This comes up every year. People worry that all members of a group, such as the cucurbits, can cross-pollinate. They can’t. Melons, squashes, and cucumbers are too different from one another to pollinate each other. That being said, varieties within a species, such as white pumpkins, Jack O’ Lantern pumpkins, and Atlantic Giant pumpkins can cross-pollinate.

Even if you have bees in your garden, you may want to try hand pollinating. Research has shown that manually applying pollen to female flowers results in larger fruit that is more likely to reach maturity. Also, the seeds within that fruit germinate faster and produce larger seedlings. This is called the xenia effect.

Did you know that researchers at Harvard are creating miniature flying robots, called RoboBees,  to be used as pollinators?

Now you know.