Plant Pollination Primer for Backyard Gardeners

Learn about insect pollination, wind pollination and hand pollination to help you plant smarter and pull in heftier harvests.


| October/November 2014



Attract plant pollinators

Gardeners can encourage successful plant pollination with certain strategies. Add water features, a resident beehive, and a diversity of colorful blooms to invite pollinators aplenty into your garden. Plant corn and other wind-pollinated crops in large blocks instead of in rows to achieve adequate pollination and a good harvest.


Illustration by Elayne Sears

As humans, it’s hard to imagine sex without the ability to move, which is the fundamental challenge of plant pollination. To make seeds, reproductive cells (called “gametes”) from separate male and female cells must join, often from separate flowers and sometimes from separate plants — but the plants can’t move to help make the miracle happen. Instead, they rely on the resources around them: wind, insects, birds and, sometimes, people.

Understanding plant pollination is more crucial than ever, as we are in the midst of a severe decline of native pollinators because of ubiquitous pesticide use in monocrop agriculture. While we may not be able to change this unsustainable practice overnight, we can make some changes in our own backyards to bolster pollinator populations and, in turn, our harvests. Numerous factors that influence successful pollination are within a gardener’s control, including planting in certain arrangements, using organic methods, encouraging wild pollinators and, when need be, actively intervening via hand pollination. The benefits of better pollination can be huge with crops that are eaten as mature, seed-bearing fruits, such as berries, corn, cucumbers, tomatoes and tree fruits.

Like most plants, food crops have sophisticated reproductive systems in place, ready to take on the pollination gamble. Delicate female parts are hidden inside the flower, safe from the elements. Plant pollen faces an out-in-the-open, hostile journey — even with a waxy coating and a stash of carbs for energy, male pollen grains must quickly find their way to a receptive female organ. There, they grow a tube that unites them with the ovary, thus forming a fertilized seed.

Self-Fertile Plants

Beans, peas and tomatoes are examples of species that are “self-fertile,” which means that all the necessities for successful pollination reside within each flower. A bit of well-timed shaking is all that’s needed to sprinkle pollen grains where they need to go, which in nature is done by wind and visits by buzzing insects. When beans, peas and tomatoes bloom but set no fruit, the weather — not a lack of pollinating insects — is usually to blame. Cold or hot weather often causes flower abnormalities that, in turn, cause fertilization to fail. To overcome weather-related crop failures, plant a few varieties known for their cold or heat tolerance — for example, ‘Glacier’ and ‘Tropic’ tomatoes. These are more likely to set fruit successfully under conditions that would cause a sensitive variety, such as ‘Mortgage Lifter,’ to shed most of its blossoms.

Insect Pollination

To produce fruit, about 35 percent of food crops require repeat visits by insect pollinators, such as bees, wasps, butterflies, flies and beetles — any creature that will crawl into the blossom, transfer pollen from the male anthers to the female stigma, and then move on to do the same to another flower. The pollen grains of insect-pollinated crops are sticky for easy transport, and many plants advertise for pollinator services with colorful flowers — visual billboards promising a sweet drink of nectar, some nutritious pollen and occasionally a safe place to sleep. Case in point: Male squash bees hide away inside bright orange squash flowers late in the day, and then the blossom closes up around the sleeping bees as night falls, protecting them from predators. Inside, the bees’ movements ensure that pollen spreads throughout the flower and all over the bees. In the morning, the guys are rested and the squash flowers are nicely pollinated.

Most flowers have not one but dozens — or even hundreds — of ovaries that need to be fertilized, so pollination usually takes place over two to three days. In any seed-bearing fruit or vegetable, each seed represents a fertilized ovary. All the little seeds on strawberries result from 16 to 25 visits by pollinating insects. In comparison, because of differences in flower design, only half as much pollinator activity is needed to produce a watermelon containing hundreds of ripening seeds.

gochamps
9/21/2014 6:01:00 PM

There has been a lot of news about bee colony collapse and the threat of poor harvests as a result. Perhaps the monoculture techniques are as much to blame. The growers of single crop orchards may need to follow the advice to plant shelter belts which attract, shelter and nourish alternative pollinators.


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