Open-Pollination

When you buy seeds or seedlings, you may see the letters “OP” somewhere on the label. These letters stand for “open-pollination” and they tell you something about the family history of that particular plant.

Female carpenter bee on escarole flower (Kate Russell)

Until the turn of the twentieth century, all of your garden plants were open-pollinated. By 1969, 71% of the U.S. corn crop was grown from hybrid seeds. This isn’t a judgment call – we have a lot of people to feed. But there are differences.

Pollen and parentage

Pollen provides half the genetic information contained in a seed. Plant ovaries contain the other half. The way that pollen gets from the male flower to the pistil, or female parts, determines if it is an heirloom, hybrid, or open-pollinated.

Hybrids and heirlooms rely on human intervention to achieve whatever results are desired. Those results may be disease resistance, heavy production, or protecting a piece of history.  Hybrids are developed on purpose to take advantage of the best characteristics of both parents. They tend to be far more fertile and productive than non-hybrids. Heirlooms and hybrids are often grown for seed in protected areas, such as greenhouses, to ensure that the genetic information stays true to the original.

Floral monoculture in a greenhouse (Uwe Driesel) Pixabay

Open-pollinated seeds throw caution to the wind. They are the wild side of seed production.

What is open-pollination?

Open-pollinated crops use natural mechanisms to spread pollen. This means self-pollination is a type of open-pollination. It also means wind, bees and other insects, birds, bats, your jacket, and anything else that comes into contact with the stamen, or male parts of a flower, may be used as a vehicle. This introduces a lot of genetic diversity into the mix.

Genetic diversity and plant health

Many heirloom crops have evolved, over countless generations, with natural resistance to many pests and diseases. They had to so that they could live long enough to reproduce. Mass-produced, monoculture hybrid crops are extremely productive. They are also very susceptible to pest and disease attacks. And, as we have all learned recently, a single virus can wreak havoc on a population.

Open-pollination leaves the door open to greater genetic diversity. This often results in improved species health, insect resilience, and disease resistance. It can also create entirely new varieties.

Breeding true

Seed saving isn’t helpful to gardeners if the resulting offspring are not edible or useful in some other way. If seeds produce offspring that are consistently identical to their parent plants, we say that they “breed true” or that they are a “standard variety”. These are seeds that can be relied upon to produce what you expect them to. Most open-pollinated and heirloom seeds breed true, but not always. Seeds produced by hybrids do not breed true and must be repurchased each year.

If you are a commercial grower in need of consistent timing, plant size, and treatment needs, hybrids are the way to go. You know what to expect and how to respond. If you are a home gardener, you are free to take things more casually.

For example, if you have a favorite tomato plant and you want seeds that breed true, you will need to protect that plant from the pollen of other tomato varieties. This can be done by planting different varieties at different times, making it so flowers are not blooming at the same time. You can isolate your tomato plant in a greenhouse or under a cover and hand-pollinate. Or, you can put distance between it and other tomato varieties.

Mini DIY greenhouse (titosoft) Pixabay

The distance needed to prevent cross-pollinating with other species depends on the mating system of a species. You can separate your modern tomato and most self-pollinating plants by 10’ or you can put miles between your spinach plants.

Miles?

Yes. Wind-pollinated crops, such as spinach and beets, produce pollen that can can fly on the lightest breeze for miles. Insect-pollinated crops require a wide range of isolation distances. The Seed Savers Exchange offers an excellent resource for isolation distances. Honestly though, most of those distances are more than we can manage in our yards. Lettuces and that prize tomato may only need 10’, but most vegetables need at least 1600’, but even that is no guarantee. If you really, really want seeds that breed true, you may have to grow only that variety and no others.

So, next time you go shopping for seeds, will you look for hybrids, heirlooms, or open-pollinated seeds? Why is that choice better for your garden?