Select a Good Tomato
Selecting a good tomato for harvesting seeds is the most important step in the process. There's no point in saving tomato seeds if you're not saving them from high-quality fruits; the resulting plants (and their fruits) will be of inferior quality.
Here's what you're looking for.
- Save seeds from an open-pollinated, rather than hybrid, tomato. Seeds saved from hybrid tomatoes won't come true, and there's no way to tell what you'll end up with. This may take a little research. If you're unsure whether the tomato you're growing is an heirloom or a hybrid, a quick internet search or a glance through a few seed catalogs will tell you what you need to know.
- Save seeds from tomatoes that are fully ripe but not over-ripe. Seeds from over-ripe fruits could already be on their way to germinating or flat-out rotting.
- Save seeds from the best-looking, best-tasting fruits on the plant. When you save from the very best, the resulting plants will be predisposed to having those same desirable qualities.
- It's fine to save seed from plants that have suffered from blight or one of the many wilts that affect tomato plants.
Slice the Tomato
Once you have your tomato selected, slice it across the equator of the fruit. This will allow you to squeeze out the seeds more easily in the next step.
Squeeze Out the Seeds
Squeeze the seeds and their surrounding gel into a plastic or glass container.
Pour two to three inches of water over the seeds you've squeezed into your container.
Label and Set Aside
Label your container, so you don't forget which variety of tomato seed you've saved. (You think you'll remember -- you won't.) Set the container in a spot where it won't be in your way or be disturbed too much. Let it sit for two to three days, until you see white mold growing on top of the water. This is a sign that the gel coating that surrounds the seeds has broken down.
Rinse and Dry
Pour off the mold, as much of the water as possible, and any seeds that are floating. (These seeds are bad, and would not have germinated, anyway.) Rinse a few times, pouring off the rinse water and any seeds or debris that float. Dump the seeds into a fine mesh strainer, and rinse well, using your fingers to dislodge any gel that is still sticking to the seeds.
Write the name of your tomato variety on a paper plate, and dump your seeds onto it. Make sure that the seeds are in a single layer, so they dry well and don't get moldy. Set the labeled plate aside for a few days so that the seeds dry completely.
Store Your Seeds
Once your seeds are completely dry, you can put them into an envelope, small baggie, or other container to store. Be sure to label them properly. It's best to store them in a cool, dry place (such as a refrigerator). When stored properly, tomato seeds will germinate reliably for up to ten years or more.