Is tomato seed fermentation required? There are quite a few methods described on the internet for collecting and cleaning tomato seed, but which one works best? How do we define ‘best’? What works well for a commercial seed company may not be the best option for a home gardener.
A very common option is the ‘tomato seed fermentation’ method. Some say that it is absolutely necessary in order to get a high germination rate but not everyone uses it and they still claim to get good germination.
It is also believed that fermentation reduces pathogens on the seed. In this post I will look at the science behind collecting and cleaning tomato seeds.
Cleaning Tomato Seed
Each tomato seed is enclosed in a gel-like sac, which is surrounded by tomato flesh. The latter part is fairly easy to remove from the seed, but even if you wash the seed in a sieve, the gel sac stays attached.
Many sources say that tomato gel or flesh will inhibit germination. If this is true, any method that does not remove it, will not work. It is claimed fermentation does remove the gel.
Tomato Seed Cleaning Methods
Here is a list of some of the methods used to clean seed. Let me know in the comments if you use a different method.
Fermentation of Tomato Seed
You scoop out the seeds from a ripe tomato, and let the mush sit for 48 hours. Some people leave it a week but that will reduce the germination rate. The resulting mush, which now includes a lot of mold, is washed and the seeds are dried.
This is probably the most popular method on the internet and it is also promoted by some government sites.
Rubbing Tomato Seed
This method does not really have a name, but ‘rubbing’ is quite descriptive.
You remove the seeds from the fruit and rub each one individually on paper towels. The gel rubs off easily and you are left with fairly clean seed. The seed is then washed, dried and and stored.
This method works quite well, and does remove all of the flesh, but it is a very tedious method. That’s not a problem for most gardeners who only need a few seeds of each variety, but if you want to collect 100 seeds – you will be busy for some time.
I have used this method personally and it produced high germination rates for me.
The ‘Do Nothing’ Method
When I first heard about this method I did not believe it would work, but many people do use it.
You extract the seeds, wash them under running water and dry them. Don’t use a paper towel because the gel around each seed sticks tightly to the paper once it is dry. To reduce this sticking problem use wax paper or a ceramic dinner plate.
What about the extra gel and flesh? You just ignore it.
According to the science we think we know, the flesh will inhibit germination and this method simply can’t work. But for some people it does work, so maybe this is all a myth? Maybe the drying process followed by several months of storage is enough to overcome the inhibition?
Tomato Detergent Wash Method
There are also several reports of treating the seeds with various home products like Clorax, backing soda, washing soda, and trisodium phosphate (TSP).
All of these products should help digest the flesh and produce clean seed. It is interesting that many people collecting heirloom seeds are organic gardeners, but when it comes to seed collection they have no problem using chemicals!
There seems to be no evidence that chemical treatment is any better than fermentation, which does not require the use of extra chemicals.
Direct Burial of Tomato Seeds
Extract the seed along with all the flesh, or even use the whole tomato. Bury it right in the garden so the seed sprouts next spring.
I am sure this works to some extent since I have seedlings popping up in the garden every spring, but it’s not very practical, in my opinion.
Testing Methods for Collecting Tomato Seed
I decided to run an experiment and test three of the above methods; fermentation, rubbing and do nothing. This video will give you the details of how the experiment was done and show you the results.
If the above video does not play, try this link: https://youtu.be/3s_mMgBuTR8
The following are my conclusions, based on my conditions and the three cultivars I tested (Garden Treasure, Garden Gem and Early Girl).
- There was no difference between cultivars.
- All three methods produced excellent germination – 100%.
- All three methods resulted in good growth of the seedlings.
- Leaving the gel and flesh on the seed did not cause any fungal growth.
The gel and flesh from tomatoes does not inhibit seed germination, or cause mold to grow, at least not after a couple of months in cold storage. The do nothing method worked just as well as the fermentation method.
Best Tomato Seed Cleaning Method for Home Gardener
I think the rub method is probably the quickest and easiest method for anyone who is collecting a few seeds for themselves. It allows you to extract the seed, and dry them immediately, without the need to wait several days for fermentation.
Best Tomato Seed Cleaning Method for Larger Quantity
If you require a larger number of seeds, the fermentation method is best. For a larger number of seeds it is the method that takes the least amount of work and it produces the cleanest seeds. This method may also have some benefit in decreasing pathogens.
For more information on doing fermentation properly have a look at this post; Best Way to Collect Tomato Seeds.
What about diseases? Does fermentation reduce diseases better than the rubbing method?
Fermentation “can destroy bacterial canker and other seed-borne diseases”. The rubbing method will not eliminate diseases that are on the surface of the seed.
If tomato canker is an issue, fermentation should last 96 hours (4 days) at a temperature about 18ºC (65ºF). This long fermentation can cause injury to the seed but is off set by a reduction of disease.
Late blight is a major problem with tomatoes and “as far as we know, the pathogen does not survive asexually from one season to the next on dried tomato seed.”
In most cases, treatment for diseases is not required after a fermentation process.