Heirloom tomatoes at a farmers’ market in San Francisco. Photo: advencap.

It is high season for tomatoes right now. Your local farmers’ market probably has a whole color spectrum of heirloom tomatoes, from red to green and purple, deepening to almost black. Heirloom tomatoes are getting more and more popular—but what does “heirloom” really mean? And how do these colorful tomatoes differ from their supermarket relatives?

What does “heirloom” mean, anyway?
In agriculture, the word “heirloom” doesn’t have a precise definition. It conjures up ideas of a food that is old fashioned and has been handed down for generations—which is as good a definition as any right now. Heirloom tomatoes are varieties that have been grown without crossbreeding for 40 or more years. This is in contrast to the typical supermarket tomatoes, which are hybrids that have been carefully crossbred to have particular characteristics. Often flavor is not at the top of the list. Instead, hybrid tomatoes are bred for things like resistance to pests and diseases, and firm flesh and thick skin—so they can be harvested by machines and emerge as whole tomatoes, not sauce.

But genetic mixing—or lack thereof—isn’t the only thing that separates the heirlooms and the hybrids. Let’s look at some heirloom tomato myths and truths, to get at other difference between the two tomatoes.

You can grow heirloom tomatoes from their seeds.
Correct. Hybrid Heirloom tomatoes breed true—if you take the seeds from your heirloom tomatoes, treat them right, and then plant them in the spring, the tomatoes you pluck from the vines in late summer will taste just like their parents tasted. One characteristic of heirloom crops is that they are open-pollinated; pollen is carried by natural mechanisms, like bees or wind. Compare this to commercially grown hybrid tomatoes, which must be pollinated by hand to ensure the correct combination of traits. This is a lot of work, but it’s necessary. Open-pollinated hybrid seeds might carry the good genes for a particular trait, or they might the carry bad genes. The only way to ensure a good crop of hybrids is to plant seeds that have been hand-pollinated so you get the right mix.

Heirloom tomatoes are organic.
Not necessarily. Often they are organic, but they would still be called heirlooms if growers treated them with pesticides and other chemicals. And growers would have good reason to spray: heirlooms don’t have the disease and pest resistance that hybrids have acquired over generations of selective breeding. Heirlooms are particularly susceptible to fungus, which makes them crack and split. Farmers growing heirlooms get one-third the yield (or even less) than they would if they were growing hybrids, because so many plants and fruits are damaged by pests and disease. This is one reason why heirloom tomatoes are so expensive.

Heirlooms taste better.
Often this is true, and there are a couple of reasons for it; some are inherent to heirlooms, and some are byproducts of the way they’re grown and harvested. An heirloom tomato plant often produces a total of only two fruits; all the plant’s reproductive efforts get concentrated into just a few tomatoes. This concentrated effort could be making the tomatoes more flavorful. And, heirlooms usually have more locules—the cavities with the seeds—than commercial hybrids. These locules are flavor centers, full of volatile compounds. Hybrids are less flavorful because they were never bred for flavor—although that is changing. Plus, heirlooms are often grown locally and allowed to ripen on the vine, as opposed to typical supermarket hybrids, which are picked when firm and green, and are ripened to redness in a warehouse with ethylene gas. When and how tomatoes ripen affects their flavor.

Heirlooms are better for you.
False: there is no evidence for this. Heirlooms don’t have more nutrients or anti-oxidants than hybrids.

A tomato tip.
Whether your shopping cart is full of heirlooms or hybrids, whether they’re red or yellow or deep purple, don’t put those tomatoes in the fridge. The cold temperature decreases whatever flavor they may have.

Seed saving is a technique that stretches to the very beginning of human agriculture.

As the summer growing season winds down, most backyard gardeners are harvesting the last few cherry tomatoes and basil leaves out of their gardens. Seeds, on the other hand, are something few gardeners gather anymore.

Seed saving is a technique that stretches to the very beginning of human agriculture.  Farmers select their best crops, save the seeds and use them for the next growing season.  Today, most backyard gardeners opt for buying seed packets or seedlings at the garden store.  But a handful of Bay Area groups are working to create local seed saving networks, where local gardeners can learn to save seeds and share them. The idea is that, over time, the projects will develop plants that are specially suited for the Bay Area's unique microclimates.

Of course, seed saving isn't quite as simple as it seems.  With plants like bean and tomatoes that largely self-pollinate, the seeds you save will most likely look their their parents. Other plants are a little more promiscuous. If you grow several kinds of squash, for example, or your neighbor is growing a different kind of squash, a few insects can cross-pollinate those plants. Those seed may sprout something surprising next year.

Mat Rogers of the Backyard Seed Vault recommends keeping it simple: start with plants that have easily saved seeds and work your way up. And don't forget that gardening is always an experiment.  Here are a few local resources:

The Backyard Seed Vault's list of seed saving resources.

Richmond Grow Seed Lending Library's list of easy and difficult seeds

The Bay Area Seed Interchange Library in Berkeley

Other local seed libraries

The Seed Savers Exchange, a national network

Listen to the Backyard Seed Banks radio report online.

37.93553 -122.34368

Some have dubbed it the "doomsday vault"; others, taking a more positive tone, call it a repository of biodiversity. However you look at it, the Global Seed Vault is a fortress. Buried under almost 500 feet of Arctic permafrost, secured against bomb blasts, earthquakes, and potential thieves, this massive seed bank, which will ultimately include samples of a large portion of the world's plant varieties, is our high-tech hope for preserving the genetic diversity that underlies the world's food supply. But despite its scope, the seed vault isn't enough.

Why a seed bank in the first place? Because industrial farming approaches have made what was once a plethora of diverse crops into something more like a set of monocultures, carefully bred to meet our standards for long distance travel, high yields, and resistance to bug and weed killers. Many scientists fear that climate change will threaten these crops, which provide us with a huge proportion of our food.

To keep growing enough food, we'll have to breed new plant varieties that fare better in higher temperatures, or in depleted soil, or under whatever challenging conditions a particular crop faces. For that, plant breeders will need to tap the genetic diversity that exists among the many varieties of any given plant. A gene that makes one kind of rice grow well in sandy soil, for example, can be transferred to another kind of rice. This is why preserving each and every variety of plant food is essential to securing our food supply.

But a seed bank, vital as it is, falls short. Why? Because how and what we eat is as much about who we are as it is about the seeds we put in the ground. We're missing something if we believe we're saving ourselves simply by saving seeds.

Don't get me wrong: Genetic diversity in edible plants is the toolbox nature gives us to feed ourselves with, and preserving it by saving seeds is central to our ability to grow and develop new crops. But, as Michael Pollan articulates in his latest book In Defense of Food, the way we eat is attached to our cultures, beliefs, languages, and rituals. We learn about growing and eating food from people who came before us, and that knowledge is as important as the food itself.

The (necessary) sterility of a seed bank doesn't capture the messy, many-threaded ways in which food and agriculture are incorporated into a society. A seed bank doesn't preserve the knowledge of how to grow its precious population, or how farming crops cooperatively might produce different results than farming them individually, or even how to make the plants into edible dishes.

If we want to ensure our food supply, we need to do more than freeze seeds. We need to also take careful notes about culture.

I began thinking about this several years ago, when I had the privilege of visiting a seed bank operated by a group called Native Seeds/SEARCHin Tucson, Arizona, when I was working on a piece about seed saving for our Science of Gardening Web site. Native Seeds/SEARCH Native Seeds/SEARCH (NS/S) was founded in 1983, when Native Americans in the region wanted to grow traditional crops and couldn't locate seeds. Since then, the organization has grown to include 4500 farmers and thousands of seed varieties developed by Native Americans in the Southwest.

NS/S doesn't just save seeds: they save the knowledge that goes with them. NS/S farmers continually plant and grow handfuls of the seed bank's reserve, refreshing the seed stock and passing along knowledge of how to best grow a particular plant. NS/S employees also collect stories from and share knowledge with Native people in the region.

Now, I'm no farmer, but it seems to me that safeguarding both the "agri-" and "-culture" of plant varieties will help us get the most out of the seeds we've saved. Otherwise, we end up seeing the security of our food as little more than a sterile set of seeds stored in a deep freeze, ready to be accessed for answers when our old farming technologies get us in trouble. But feeding ourselves is hardly a sterile affair: we grow, prepare, and consume food in a complex context of environment and humanity. I, for one, think our tendency to dismiss that larger picture is what's gotten us into this biodiversity problem in the first place.

Robin Marks is a journalist and science writer who current serves as a Multimedia Projects Developer for the Exploratorium in San Francisco, CA.