Heirlooms, Hybrids, and GMOs: What’s the Difference?

One of the fundamentals of understanding tomato varieties is knowing the difference between heirlooms and hybrids. Another important distinction is to understand that a hybrid is not the same as a genetically modified organism (GMO). Here at the World Tomato Society, we want people to know such differences in case they want to save seeds, ensure their food supply is safe, be informed of the latest technology in plant breeding, or understand debates around food justice issues.

Seed-saving techniques and requirements vary throughout different plant species. To convey these concepts in the clearest manner, we have limited this particular article to tomatoes. Plant genetics is a complex science, but here we provide the most pertinent information for the home gardener regarding tomato cultivars.


One cannot talk about heirloom tomatoes without a discussion of seed saving. Also known as open-pollinated, heirlooms derive their name from the fact that historically, families would save seeds from their gardens and hand them down from generation to generation. The term “open-pollinated” means that one can save the seed from a specific variety and have faith that sowing those saved seeds the next year will usually result in a similar plant.

Seed saving is quite the art and science, and not so easily done as one would imagine. One must take into account the health of the mother plant, the proper maturity of the seed harvested, techniques that ensure the fertility of saved seeds, and a robust population sample—this refers to the quantity of mother plants from which one has saved seeds.

While maintaining the genetic integrity of distinct varietals is important, a seed saver’s duty is to ensure that any negative inherited traits are dispersed across a large population of next-generation plants. The purpose of a large population sample is not to intentionally disperse negative traits but instead to select seeds from a range of high-performing, healthy plants. Genetic mutations occur naturally, and they are not necessarily negative; however, if one only saves seeds from a single fruit (or single plant), mutations can be more frequent in the following generation. A high-enough concentration of mutations can result in an entirely new cultivar or an infertile plant.

Tomatoes are self-pollinating, meaning that they have both male and female reproductive organs, so they do not cross-pollinate readily. Therefore, an isolation distance—the approximate distance required between other species and varietals of the same species to ensure that cross-pollination does not occur—between your saved tomato cultivar and a potential cross-pollinator is less of a concern than in other plant species.

Saving seeds from heirloom varieties that perform well in your garden can help you develop your own strain of heirloom plant that is specifically acclimated to your personal terroir. It’s a plant that you know loves your garden and soil; it prefers the weather and temperature range, and thrives in your personal corner of the world. Biodynamic farmers are required to do much of their own seed saving because it reduces their reliance on outside sources.

We at World Tomato Society urge gardeners to save as many seed varieties as possible. Make sure to research seed-saving techniques specific to your target plant. Keep in mind potential cross-pollination and isolation distances to ensure a good future year’s crop.

The world is losing genetic diversity in fruits and vegetables because many gardeners have stopped saving seeds of generations-old heirlooms. We want to get back to a system of seed saving in order to grow terroir-specific varieties, reduce our reliance on outside inputs, and preserve many special varieties of heirloom vegetables that would otherwise be lost.

Here’s a tomato seed-saving walkthrough by Madeline Rains. Keep an eye out for the World Tomato Society’s seed-saving tutorial to be published later in the season.


Hybrid fruits and vegetables have two or more genetic parents. That means that the hybridizer purposely took pollen from the father plant and inseminated the flowers of the mother plant, resulting in the following generation having characteristics of both the mother and father plants. For example, a hybrid beefsteak tomato is usually the offspring of a red cherry tomato and a not-so-productive large tomato. The hybridizer takes the pollen from one and inseminates it into the flower of the other to create a next-generation beefsteak tomato with a higher yield.

Hybridizers have many goals in hybridizing plant varieties. To limit this discussion to tomatoes, hybridizers are looking for several characteristics in tomatoes they produce; usually those qualities have nothing to do with taste. Hybridizers typically have a commercial interest in mind, such as a higher yield, uniformity of fruit size and shape, reduction of blemish frequency, disease and/or pest resistance, determinate plant height and ripening time, and, most often, the ability to stay fresh longer on a supermarket shelf. Much of these criteria do not concern the normal gardener, who wants a tasty, homegrown tomato. Many home gardeners tend to choose heirlooms over hybrids because the former almost always taste better.

Because hybrid plants require human intervention to perform this cross-pollination, hybrid seeds are necessarily more expensive than heirloom or open-pollinated seeds. One cannot save seeds from a hybrid, such as Early Girl, and expect the same fruit the following year. The saved seed from a hybrid tomato will revert back to one of its genetic parents.

Have you ever had a volunteer tomato plant in your garden? Usually, it turns out to be a red cherry tomato, even if you had not planted any red cherry tomatoes the previous year. That is a hybrid seed reverting back to one of its genetic parents, most commonly a red cherry. (By the way, Monsanto, through its subsidiary, Seminis, has purchased the rights to Early Girl hybrid seeds.)

Hybrid tomatoes have a place in many gardens. New gardeners attempting to cut back on maintenance, those who don’t have the time nor the expertise to care for their tomatoes well, or folks who have a history of disease in their garden may prefer the benefits of hybrids. Hybrids can help with these ailments and lack of gardening experience. Note, though, that when a seed vendor claims their hybrid is resistant to a certain disease, this does not mean that the tomato will never contract that disease but rather that the tomato will take longer to succumb to it.

Genetically Modified Organisms (GMOs)

A GMO is any organism whose genetic material has been altered using genetic engineering technologies. GMOs are the source of genetically modified foods, and are also widely used in scientific research and to produce goods other than food. The term “GMO” is close to the technical legal term “living modified organism,” as defined in the Cartagena Protocol on Biosafety, which regulates international trade in living GMOs.

The World Health Organization states that GMOs are defined as “organisms in which the genetic material has been altered in a way that does not occur naturally.” Recombinant DNA technology, also called genetic engineering, allows selected individual genes to be transferred from one organism to another, also between nonrelated species. The resulting organism is said to be genetically modified, genetically engineered, or transgenic. The top genetically engineered crops in the United States are corn, soy, canola, and cotton, but not tomatoes, so far.

In agriculture, currently marketed genetically engineered crops have traits such as pest resistance, herbicide resistance, increased nutritional value, or production of valuable goods such as drugs. Products under development include crops that are able to thrive in environmental conditions outside the species’ native range or in changed conditions in their own range, such as drought or salt resistance. Products that existed and have been withdrawn from the marketplace include those with extended product shelf life such as the Flavr Savr Tomato.

The biggest aspect of the debate on food derived from DNA technology is whether GMOs are helpful or harmful to humans and the environment. Some arguments against GMOs posit that GMO crops can contaminate non-GMO crops through cross-pollination. GMO skeptics claim that weeds and insects can develop resistance to herbicides and pesticides used heavily on GMO crops. They say these pests can mutate such that no pesticide, organic or synthetic, will be able to control them. Opponents of GMOs also say that genetically modified food could make disease-causing bacteria more resistant to antibiotics. Proponents of GMOs state that it is a way to feed starving populations and increase our planet’s ability to produce food, and that these organisms are completely safe.

The GMO debate continues to manifest sharp divisions in politics and communities. The World Tomato Society believes that we must stay informed of ongoing research regarding the safety of genetic modification. We believe that people should have the right to know whether or not they are consuming genetically modified foods so they can make their own choices regarding what is safe for their families.

Plant genetics is more complicated than new gardeners may realize. There are many factors to consider when deciding what is right for your garden. Now that you know about differences among heirlooms, hybrids, and GMOs, you have more knowledge to make informed choices about purchasing or saving seeds.