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Last year, I saved some seeds from tomatoes that I have grown. In some batches, the seeds turned completely black.

We have been having a bad yield this year of tomatoes and I was wondering if this could be the reason.

I feel the reason why they turned black was that they were not thoroughly washed thus leaving that gooey texture on the seed.

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By a gooey texture, I suppose you mean they were dried with the gel sacks on. Fresh tomato seeds generally are surrounded by gel sacks. Do not confuse gel sacks with the seed coat (the seed coat is shell of the seed). Gel sacks are normally removed during the seed-saving process (before drying) via fermentation.

If you dry seeds without removing the gel sacks, they may appear red, sticky, and messy, and they may (in some cases) become very dark. As long as they didn't mold or something, in my experience they should still be able to sprout with a reasonable germination rate (although I recommend overseeding to be sure). They can remain viable in this state for at least a few years, in a semi-arid climate.

You should note, however, that many people believe gel sacks contain substances that inhibit germination. Whether or not this is true, I've planted lots of them before (overseeding when I did), and lots of plants sprouted in each container.

However, there are some problems with leaving the gel sacks on:

  • A lot of the tomato seeds that I planted (wherein they had the gel sacks on) were not able to escape from their seed coats after sprouting up through the soil.
  • They seemed to be infected with a fungus, like some kind of Alternaria (which was not evident before the transplant).
  • They don't look professional, like nicely brushed horses.
  • It puts a damper on trading or giving away the seeds.

So, when initially saving your fresh seeds, I recommend removing the gel sacks, either via fermentation, or some other method. Fermentation has a number of advantages, and it's the most well-renown way of saving tomato seeds.

Instead of fermenting, I personally usually rub the gel sacks off with my thumb with water running over it, in a strainer, and then I put them in labeled empty herbal tea bags, and zap them in water with a Z4EX for 45 minutes, 15 minutes per frequency; for me, that works great (but I'm the only one who does it, to my knowledge, and I can't guarantee its efficacy to you, for liability reasons, as all my experience is anecdotal, rather than proven by respected scientific studies). Sometimes I freeze my dry seeds before planting as an extra precaution, since some pathogens are cold-intolerant (but mostly I like to do that with seeds I've been traded). I dry my zapped seeds in the same herbal tea bags, on brown paper bags, in a room with a decently strong fan, and they dry fast, without mold, that way (even though they're not spread out). I keep the seeds in the herbal tea bags until I want to use them (then I cut them open, get the seeds I plan to use out, and put the open herbal tea bag and its seeds in a clear plastic bead bag, like a miniature Ziplock bag; I usually use the 2"x3" ones).

The reason I zap instead of fermenting is because I grow a lot of kinds of tomatoes, and I prefer the seed-saving process to be quick; plus, it only takes 1 jar per zapping session (and I can do maybe 15 bags of tomatoes per session). I'm not the owner of the house, and the owner would object to me putting fermenting jars of tomatoes all over our surfaces.

If you have seeds that have been dried with the gel sacks on (and it sounds like you do), then directly before planting, I recommend freezing the dry seeds for at least a few hours (never freeze wet seeds), and then soaking them in water with hydrogen peroxide for 30 minutes or more (they can soak for hours and still be viable). The hydrogen peroxide will eat the gel sacks away.

Some people clean their seeds with other substances.

Some people put their fresh wet seeds in a blender on low for a second or so (to remove the gel sacks). That won't remove any diseases from within the seed itself, though, should there be pathogens in it (but removing the gel sacks should significantly reduce the odds of diseased seeds). Not all seeds survive the blender process, but many usually do.

However you save your seeds, I recommend drying them on brown paper bags or something similarly as efficacious. This helps them dry fast and reduces the odds of them molding. To reduce odds even further (or to speed drying), have a fan running in the room where they're drying. Warmth will also make them dry faster.

If you removed the gel sacks somehow, and the seeds are black, then there are a number of possibilities:

  1. The seeds are rotten.
  2. The seed coats just mysteriously turned black and the seeds are fine (I've had that happen before). You can dissect the seed to see if the inside is rotten or not (it should be a cream color). Or, you can just plant them and see if they grow.
  3. The seeds are rotting, but not fully rotten. In this case, you should see black specks on the seeds. This is common in ripe and overripe tomatoes. These may or may not germinate; I don't know (I don't usually plant those ones).

Diseases can affect the number of fruits produced by a plant, sometimes. So, it's possible your seeds had a disease that inhibited production. However, I'm guessing something else is to blame, if the plants and fruits otherwise looked fine. I might guess the tomatoes needed more potassium, organic matter, compost, or something. Or, it's possible the plants weren't transplanted at the right time, or else they were too young at transplant time to produce as much as a store-bought plant. It's also possible that you grew different kinds of tomatoes than usual, and your usual were just more prolific. It's also possible that you didn't harden off your plants well enough. It's also possible it was just an off year. It's also possible that you planted F2 hybrid seed, which can be less prolific than the F1 parent at times.

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  • Have you ever dried your seeds unwashed? Did it impact your germination rate?
    – Mark Odey
    May 5 at 15:58
  • Unwashed? I don't recommend it, but yes, I've done it. Germination rates seemed fine (I didn't count the percentage that sprouted), but it probably increased the number of seedlings that couldn't escape the seed coat, and I think it spread alternaria to the plants. Also, it didn't look great, and the seeds stuck to whatever they dried on (and each other). To avoid disease, and to increase aesthetics, I recommend removing the gel sacks, either via fermentation, or some other reliable process. May 6 at 3:02
  • If you have dried unwashed seeds, you can freeze them (dry) for a while, and then soak in water with H202 before planting. That should reduce the incidence of disease. Some people soak them in other stuff instead of H202. Freezing may only kill cold-intolerant pathogens. May 6 at 3:04
  • I believe I misunderstood your question. So, I reformed my answer. May 6 at 5:04

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