Senior Gardening

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Saving Tomato Seed
October 12, 2009

Lots of folks wonder whether they can save viable seed from their tomato plants. The answer to such questions is a qualified "Yes." I have to add here at the beginning of this feature that you only want to save tomato seed from open pollinated varieties of tomatoes.

Ripe tomatoesMost tomato plants sold these days in garden shops are hybrid varieties, produced by crossing one plant with another to produce a hybrid with, hopefully, the best qualities of each of the parent plants. Unfortunately, saving seed from hybrids will usually not result in a near clone of your tomato plant, but something from the heritage of the parents...often with undesirable traits.

If you're unsure whether the tomato variety you wish to save seed from is open pollinated or a hybrid, try Googling its name with the word "tomato" (i.e., moira tomato). In your search results, you may find your answer. If you see "hybrid" or "F1," it's a hybrid. You can also go to one of the many garden sites that carry lists and evaluations of various tomato varieties. I currently use Dave's Garden for such things. And you may already have the information at your fingertips in an old garden catalog.

In selecting tomatoes for saving seed, you want to choose your very best fruit from your very best plants. The tomatoes need to be ripe and disease free from a plant with a good growth habit. Here at the Senior Garden, that presents a bit of a challenge, as we've picked up a few tomato diseases over the years. Our tomatoes for seed saving this year were planted in an area where we haven't previously grown tomatoes to avoid carrying over any soil borne tomato diseases. The area was also about a hundred yards away from our other tomato varieties, which should prevent any chance of cross-pollination with our other tomato varieties. If you're just saving seed for yourself, such isolation really isn't necessary.

And of course, work with saving just one variety of tomato at a time.

How you get your seed out of your tomatoes is a matter of personal preference. Since I only do a few tomatoes at a time, I first wash and core the tomatoes. I expose the tomato's seed cavities by slicing off the top and bottom of the tomato. Then I slice out the outer side from each seed cavity of the tomato and scrape the seeds and the surrounding gel into a plastic container. Plastic or glass is preferred for processing the tomato seed, as tomatoes are an acid fruit and may react with a metal container. Also note that you want to keep your slurry of tomato seed in a container with a tightly fitting lid.

Seed cells visible Harvesting tomato seed
Side removed Seed slurry in container

You probably could just collect the solid material coming out of the waste end of a Squeezo Strainer if you wanted to save thousands of tomato seeds! Just remember to get the seed and the surrounding gel.

Growing Garden SeedsSet aside your covered container of tomato seeds and gel. You will want to let the slurry sit and ferment. Depending on your ambient temperature, the process may take 2-4 days. According to Rob Johnston, Jr.'s Growing garden seeds: A manual for gardeners and small farmers (Also available from Amazon), the process "requires about 4 days at around 60o F, about 2 days at 80o F." He recommends cooler temperatures (60-70o F) "to prolong fermentation for over 3 days so that the bacteria which could cause canker disease in the following crop are destroyed."

Stir your fermenting tomato seed mixture daily, if not several times a day. Since I keep our fermenting seed in a covered plastic container, I just shake the container sideways several times a day over the fermentation period.

Fermented tomato slurry

After three or four days of fermentation, you should have a really nasty smelling solution such as the one pictured above. At this point I add water to the seed and float off mold, light seeds (which usually aren't viable) and plant material. I do this rinse four or five times, sometimes letting the seed sit for a few hours in between rinses.

The fermentation step should separate all the plant material from the seeds. If it hasn't, gently use your fingers to tease off the plant material from the seed before washing it off.

Hot Water Treatment (optional)

Since I offer our Moira tomato seed to other gardeners via the Seed Savers Exchange annual yearbook, I chose in 2010 to begin using hot water treatment for all our tomato seed. Our seed tomatoes were all picked from uninfected plants, but we also had some diseased plants on our property. So just to be sure, I added this step. If you are sure your plants are healthy, definitely omit this treatment, as it can decrease germination rates.

Pyrex cup and Weston darkroom thermometerI use a two cup Pyrex measuring cup with my trusty, 40+ year-old Weston darkroom thermometer to hot water treat our tomato seed. I begin with some warm water in the measuring cup and add the rinsed tomato seed right from the plastic fermentation tub.

Holding water temperature at 122 F
A hot water bath helps in holding the right temperature

I then add water from a teapot on the stove until I gradually get the water temperature to 122o F. Holding the seed at that temperature for the recommended 25 minutes isn't too hard, as I just keep adding a bit of hot water to the cup whenever the temperature begins to dip. Keeping the pyrex measuring cup in a sink of hot water also helps maintain the proper temperature.

Note that the type thermometer I use is most accurate between 68-80o F, but I've tested this one with a mercury thermometer and found it pretty close at higher temperatures. Also note that we use hot water from a teapot, as our hot water tap is soft water that contains salt residue. Our cold water at the kitchen sink, which I fill the teapot with, bypasses our water softener.

After the 25 minute treatment period, I begin adding cooler water to the cup, draining it down, and adding more cool water until I get it close to room temperature. I'm not sure if one can thermal shock tomato seed, but I've sure cracked a lot of warm, grape tomatoes from the garden with a cold water rinse!

If you think you need to hot water treat your tomato or other garden seed, I've added a couple of excellent sources of information on the subject in the links section at the end of this feature.

Drying

Drying tomato seedsOnce you have as much of the plant material removed as possible, drain your seeds. I use a small kitchen strainer which allows me to further rinse the seed, sometimes using the kitchen sprayer to add a little pressure to dislodge plant material that sometimes stubbornly adheres to the seed. Then turn your seed out on a paper towel or coffee filter. Separate the seed as much as possible. Placed in a warm, sunny spot, the seed should dry in just a day or so.

Pepper seed in drying jarI like to move the seed to a coated paper plate as soon as the paper towel looks dry so that I can begin gently separating seed that is stuck together. It also helps prevent the seed from bonding to the paper towel. When the seed is completely dry, rub any remaining clusters of seeds that are stuck together to separate them.

At this point, your seed is probably ready to store. I've added one more step to my process, as I tend to store seed in the freezer for long periods of time (think decades, not months or years).

Commercial seed houses dry their seed far below normal household humidity to maintain seed vitality in storage. While most of us don't have the equipment for such drying, one can further dry their seed by just putting the "dried" seed in a jar with some powdered milk for a day or two! The powdered milk should absorb a bit more moisture from the seed.

I goofed and didn't get a shot of tomato seed in the jar with powdered milk held in the top with a scrap of an old t-shirt. But I did have a shot of some pepper seed getting the same drying treatment.

Storing Your Seed

I've used a variety of packages for saving tomato and other seeds over the years. I think the key to preserving viable seed is to get the seed really dry, get the air out of your package, and store it in a cool, dry, dark location. Seed packets in a mason jar with a tight fitting lid stored on a cool shelf should last for several years. If you have an amber or dark green mason jar with a tight fitting lid, so much the better.

Since we keep seed for many years, we freeze our seed in a manual defrosting freezer. The warming and cooling of a self-defrosting freezer can weaken seed viability.

Tomato seed packages

I used homemade aluminum foil packets for our saved tomato seed this year. I made a new, separate packet for each batch of seed I saved and then placed them in a small freezer bag with the air squeezed out. That freezer bag went into a larger freezer bag that holds all of my tomato seed. And it all will eventually go out to our chest type, non-self-defrosting freezer in our garage for the winter.

Foil packets, small brown envelopes, and glassine envelopes all work well for storing saved seed. I used heavy duty foil, as I had plenty of it on hand. The Stokes seed packet shown above carries a date of January, 1987 and still has a few seeds in it. I'm not really sure if my tomato plants for seed saving this year came from it or one of my past batches of saved seed from 1984 or 1992. The point here is that freezing tomato seed retains its viability for a very long time. But also note that I put around a hundred seeds from the various packets of Moira tomato seed into a six inch pot and only got about fourteen tomato seedlings from the planting. I almost lost my start of Moira tomatoes because I didn't grow them out and save seed from them for over 20 years. Duh!

Germination testGermination testOne other optional step you may want to take is to do a quick germination test of your dried, saved seed. To do so, just count out ten tomato seeds and space them on half of a paper towel or on a coffee filter. Fold the towel over them and wet it a good bit. Place the wet paper towel with your seeds in a plastic bag (ziplock or??), and put it in a dark, warm (75-80o F) spot. After a few days, open it up and check for sprouts. At about the 7-10 day mark, you can safely count the sprouts and figure your approximate germination percentage.

That's about all there is to it. Saving tomato seed is an easy process.

The Seed Savers Exchange

I became a member of the Seed Savers Exchange (SSE) in the mid to late 70's. I first saved and offered several varieties of tomato seed, later working to help preserve the old, open pollinated Reid's Yellow Dent field corn when we had a farm. I let my membership in the excellent organization lapse after giving up farming in 1989, but rejoined a few years later.

Over the last few years, we've been able to share seed from Moira, Quinte, and Earlirouge tomatoes, Earliest Red Sweet peppers, Alma and Feher Ozon paprika peppers, and Japanese Long Pickling cucumbers via the exchange. Ordering from the yearbook is restricted to SSE members, although non-members may view member offerings through the Exchange web site. Membership runs $40 per year. (Reduced income memberships are also available.)

Helpful Links

Below are some links I found interesting about saving tomato seed and tomato plant diseases.

Hot Water Treatment of Tomato (and other) Seed

Video links:

There are lots of videos on YouTube about saving tomato seeds, but almost all of them omit the critical information that one needs to save seed only from open pollinated tomatoes!

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