Saving tomato seed is easy because, unlike many vegetables and fruits, the flowers are usually perfect and self-fertile, which means that each flower contains male and female components and pollinates itself.
So, with some exceptions, if you save seed from one tomato, the next generation of plants – the tomato plants that grow from those seeds – are likely to be similar to the parent plants. These seeds are said to be true to form. That is, they produce plants characteristic of the variety. Sometimes they are said to be true breeding.
For the above to be true, you have to start with open-pollinated tomatoes, as opposed to hybrids where pollen from one variety is collected and used to pollinate emasculated flowers of another variety. Seeds from hybrid tomatoes are highly variable in their genetic makeup and will produce a mixed bag of plants with a full range of characteristics. So look for plants or seeds that are labeled “open pollinated” or “heirloom” rather than hybrid or F1.
The key to saving tomato seeds is to “ferment” the seeds, a process that eliminates certain seed-borne diseases and helps with pulp removal. The process is simple. Take the tomato from which you want to save seeds. Cut it in half. Squish the inside juice, pulp and seed into a container of some kind, a cup, for instance. You can put several tomatoes in the same cup; just be sure to keep separate varieties separate and label them so you don’t get your Brandywine mixed up with your yellow cherry. Add a dash of water.
Let the cup sit in a warm spot (about 70 degrees) but not in direct sunlight. Stir once a day. On the third day (give or take), a layer of scum will begin to form on the surface of the liquid. Let this scum?– a fungus – work its magic for three more days. The fungal action makes the seed quicker to germinate and destroys some disease agents as well.
Good seed will sink to the bottom; bad seed floats on the top. At least three days after the fungus appears, pour off the top-floating layer and rinse the remaining tomato seeds. Pour out onto newspaper or a paper towel and let them dry for several days. Store in a cool, dry place until next spring.