Like peas, beans and lettuce, tomatoes are well suited for seed saving in the home garden. You can save excellent tomato seeds from a small number of plants with different varieties growing right next to each other.
In addition to being inbreeding self-pollinators, this is made possible by the fact that the male part of the flower covers the female part so completely that—if and when the flower is visited by a pollinator—all it does is knock the pollen directly from the male part right into the female part of the same flower.
It can’t even get to the female part. Cool, right? Like nearly everything in nature, however, there always needs to be an exception, and in this case, it’s the potato-leaf varieties of tomatoes.
Keep ‘Em Separated
The leaves of most tomato plants look kind of like oak leaves. There are a few, however, like Brandywine and Pruden’s Purple, that have more oval-shaped leaves. These look very much like the leaves of a potato plant (hence the name).
In addition to this unusual shape, these varieties have longer-than-usual female flower parts that stick out above the male parts. These promiscuous varieties face the risk of outside pollination. They require a little separation from other tomatoes.
This is just an issue for that tomato, though, not for the other ones. You could grow a Brandywine next to a Purple Cherokee and a Yellow Pear, and the latter two won’t have a problem.
Once you have a ripe tomato (this could be one that is vine-ripened, or one picked in that “almost ripe” state and allowed to ripen on the windowsill), the next step is to ferment the seed. This is not difficult at all, but it’s necessary when you save tomato seeds for two reasons.
First, you probably have noticed that the seeds in a tomato are surrounded by a little membrane that makes them look like a frog’s egg. This must be fermented off so that the seed can be properly stored.
Second, the fermentation prevents transmission of a number of tomato diseases. These include the much-feared late blight, among others.
To do the fermentation, squeeze some seeds along with some tomato juice into a small jar. For very dry past tomatoes, I sometimes add just a little bit of water.
Place the jar, uncovered, in a place out of direct sunlight where it won’t be disturbed. I like a north-east-facing window.
The next step I recommend is telling your spouse, partner or other housemate what you are up to. I’ve lost more than one jar of fermenting seed to the diligent kitchen cleaning of my wife. (How can I complain, really, when she’s the one that cleaned up dinner that night!)
Speaking of spouses, they are often the ones that will tell you when the fermentation is done because a green film will appear on the surface of the liquid and it will start to smell a little.
This will take three to five days.
If you leave them in too long, the danger is that they can start to sprout. I’ve not had this issue leaving them there up to seven days. But if you have the time and the seeds are done, there’s no reason to wait.
To finish the job, take the jar of fermented seed, add a little water, and stir with a fork to make sure the seeds are well separated from the other material. (This is often unnecessary if the fermentation is complete.)
Then pour off most of the water. Most of the seeds will go to the bottom while the fermented solids can be poured off the top. You will pour out a few seeds, too. But like with lettuce seeds that we blow into the wind, these will generally not be the healthy, viable seeds that you want.
Add some more water to the mixture and repeat this three to four times until the water runs clear. Then pour off as much water as you can and pour the damp seeds off onto a plate to dry.
You’ll want to separate them while they are still damp. Once they dry, it’ll be very difficult to do so.
I just put them on a dinner plate on top of the fridge, and the next morning they are dry. You can dry them on paper towels or newspaper, too, but I find that they stick to those.
Once the tomato seeds are all dry, they’re ready to save in storage for next year!
This article originally appeared in the September/October 2020 issue of Hobby Farms magazine. It was excerpted with permission from Beginning Seed Saving for the Home Gardener by James Ulager, from New Society Publishers (2019).