Written by TagTomat 20 Sep 2023 08:52

Harvesting and Fermentation of Tomato Seeds for Next Year's Cultivation

Tomato season is well underway, although many of us have felt like we waited a long time for ripe tomatoes this year. However, our tomatoes are now ripening on the roof of a dumpster shed in Nørrebro. This means that we are tasting and assessing our many different tomato varieties and selecting those we will grow again next year.

If you continue reading, we will guide you on how to harvest and ferment seeds from the ripe tomatoes you wish to cultivate next year, and what to pay attention to when harvesting your own seeds.

Which tomatoes are suitable for seed saving?

First, make sure your tomato varieties are suitable for seed saving. Some varieties may yield unpredictable results and are not ideal for seed saving.

Harvest Seeds from Healthy, Ripe, and Open-Pollinated Varieties

It is essential that the plant and the tomato you are harvesting from are healthy to prevent the transfer of any diseases. Choose tomatoes for seed saving from your healthiest plant, selecting the healthiest-looking tomatoes on the plant. Additionally, the tomatoes must be very ripe, preferably overripe, to ensure that the seeds are mature and capable of germinating. Ripe tomatoes will feel soft when you press them.

If you want to ensure tomatoes of the same kind as the ones you are harvesting seeds from, it is important to choose open-pollinated varieties. This means you should avoid taking seeds from varieties labelled as F1 hybrids if you wish to cultivate the exact same tomato you are harvesting seeds from. F1 hybrids can potentially yield completely different tomatoes from the ones you are collecting. If you purchase seeds, it will be indicated on the packet if it is an F1 hybrid. Tomatoes from the supermarket are often F1 hybrids.


Guide: Harvesting tomato seeds with the fermentation method

It is possible to harvest tomato seeds in several different ways; however, fermentation helps dissolve the gel that surrounds the seeds and prevents the growth of bacteria and diseases that could affect the seeds and plants. We will guide you on how to ferment seeds for next year's tomato cultivation.

 You will need:

  • Healthy, ripe tomatoes from which you wish to collect seeds for next year's tomato season.
  • A glass jar for each tomato variety you wish to ferment. Each variety needs its own jar; these can be jars or small liqueur glasses. They should not be too large unless you plan to collect a large quantity of seeds.
  • A waterproof marker to label the jars.
  • A chopping board.
  • A knife.
  • A teaspoon.
  • A fine-meshed sieve.
  • Coffee filters.


Here's how to do it:


1. Gather all your tools and ensure that your jars are clean. Good hygiene is important. Wash the selected tomatoes, making sure they are very ripe, healthy, and free of diseases.

2. Cut up your tomatoes, scrape out the insides containing seeds, and place them into the corresponding glass jars. Label each jar with the variety name. Work with one variety at a time to avoid mixing them up.

3. If your tomatoes are a bit dry or the jars are too large, add a little water. The more water you add, the longer the fermentation will take, and there is a risk that the seeds may begin to sprout. However, there should be enough fluid for the seeds not to dry out. Stir well to separate the seeds from the flesh. Repeat steps 1-3 if you are harvesting seeds from different varieties and clean your tools between each variety.

4. Place the jars in a warm location away from direct sunlight and consider stirring each jar once a day. Leave the jars for about three days until a layer of mould forms on the surface. When there is a layer of mould, it indicates that the seeds have fermented, and the gel around the tomato seeds has loosened, making the seeds ready for further processing.


5. Most of the seeds should have settled at the bottom of the jars by now and are healthy. Any seeds on the surface should be flushed out with the fluid. Remove the mould layer with a spoon and pour out as much fluid as possible without losing the seeds at the bottom.

6. Rinse the seeds by transferring them to a larger glass or bowl and pouring water over them. Stir the seeds with a spoon or whisk. Discard any seeds that float to the surface, as these may not be healthy. Transfer the remaining seeds to a sieve, ensuring they won't fall through. Rinse the seeds thoroughly with tap water, gently rubbing them to remove any remaining gel. Make sure all seeds are clean.

7. Allow the seeds to dry completely for about a week. It is crucial that the seeds are completely dry before storing them, as moisture can cause them to rot. Carefully separate the seeds from each other. They are now ready to be placed in coffee filters or paper bags. Store them in a dry, dark, and cool place until you need them for pre-germination next year. Label the coffee filters with the variety name and year. When stored in a dry, dark, and cool place, the seeds can last for many years.

Green front 

Team TagTomat