How to Save Tomato Seeds (and Why Fermentation Helps)
Saving tomato seeds is easy once you know the trick — fermenting them. Here is the full method, from picking the fruit to storing dry seed.
Quick answer
Pick a ripe tomato, ferment the seeds 2–4 days, then dry them
- Best fruit
- A fully ripe, open-pollinated (heirloom) tomato — not an F1 hybrid.
- Ferment
- Seeds and gel in a jar of water for 2–4 days, until they sink and mould forms.
- Dry
- Rinse, spread on a plate or paper, and dry until the seeds snap when bent (1–2 weeks).
- Store
- Cool, dark and dry; tomato seed usually keeps about 4–6 years.
Why ferment tomato seeds?
Tomato seeds are wrapped in a gel sac that keeps them dormant and stops them sprouting inside the fruit. In nature that gel is broken down by fermentation; when you save seeds at home, you copy the same process in a jar. Skip it and the gel can harbour mould during drying and slow germination later.
The fermentation will not make a bad seed good, though. What actually decides whether your saved seed is worth keeping is the plant it came from — which is why the next section matters.
Not every tomato will come true
Seed from an F1 hybrid will grow into a plant that does not match the parent. Save from an open-pollinated or heirloom variety instead — see whether you can save seed from a supermarket tomato.
Choosing the right tomato
- Use a fully ripe fruit, not one that is still firm or starting to rot. Ripe seed is mature seed.
- Pick your best plant — flavour, health and yield are all heritable, so save from the fruit you would grow again.
- Avoid F1 hybrids if you want the same tomato next year.
- Keep varieties apart if you also grow others close by; tomatoes mostly self-pollinate, but crossing does happen.
The method, step by step
- Cut the tomato and scoop the seeds. Halve it and squeeze or spoon the seeds and gel into a small jar.
- Add about twice as much water. Stir, then cover loosely and leave at room temperature — not in the fridge.
- Wait 2–4 days. Stir once a day. A layer of mould may form and the good seeds will sink.
- Pour off the debris. Add water, swirl, and tip away the floating pulp and any seeds that float with it — floating seed is usually empty.
- Rinse the sunk seeds in a fine sieve until the water runs clean.
On timing, the sources are consistent but not identical: RHS and Garden Organic both describe a few days of fermentation, with a range of roughly 2–4 days. In warm weather it moves faster; if the jar starts to smell strongly or the seeds look soft, rinse and move on.
Drying and storing
Spread the rinsed seeds thinly on a china plate, a coffee filter or greaseproof paper. Do not use kitchen roll, which the seeds stick to. Leave them somewhere airy and out of direct sun.
- Dry for 1–2 weeks. Turn them once a day so they do not clump.
- Test dryness: a properly dry tomato seed snaps or shatters when you bend it. If it bends, keep drying.
- Store cool, dark and dry — a sealed jar or paper packet in a cool room. See how long seeds last and how to test germination before sowing.
Tomato seed is one of the longer-lived vegetable seeds, commonly given as about 4–6 years under good conditions — but storage conditions matter more than any single number.
Labelling and keeping enough seed
One tomato gives more seed than most gardeners need, so store a spoonful and keep a clearly-labelled packet as a backup. Write the variety, the year, and whether it was open-pollinated, so future-you knows what the seeds are.
- Keep more than you think. Two or three fruits' worth covers losses to poor germination and damp storage.
- Label it immediately. Once the seeds are dry and loose, they all look alike.
- Share the surplus. Seed swaps are one reason open-pollinated varieties survive.
If you save from more than one variety, keep the jars separate and clean between them — and remember the caveat in saving from shop-bought tomatoes: hybrids do not come true.
Common mistakes when saving tomato seed
- Saving from an F1 hybrid. The seed grows, but the fruit will not match. Save only from open-pollinated varieties, or accept the surprise.
- Not fermenting long enough. A single day leaves gel on the seed, which encourages mould in storage. Two to four days is the usual window.
- Drying on kitchen paper. The seeds glue themselves to it. Use a plate, a coffee filter or greaseproof paper instead.
- Storing before fully dry. If a seed bends rather than snaps, it is not ready — damp seed rots in the jar.
- Mixing varieties. Once dry, tomato seeds look identical, so label jars immediately.
How many tomatoes do you need?
A single medium tomato holds far more seed than most gardeners will ever sow — often enough for several seasons. Two or three fruits from a variety you like is plenty; there is no advantage in processing every tomato on the plant. If you grow more than one variety, process them one at a time and rinse your hands and tools in between, since tomato pollen and gel can carry across. Keep the surplus labelled and share it — seed swaps are how open-pollinated varieties stay in circulation.
Frequently asked questions
Can I skip the fermentation?
You can rinse and dry the seeds straight away, and many people do. Fermenting simply cleans the seed better and mimics the natural process. If you skip it, rinse thoroughly and dry fast to avoid mould.
Do I have to ferment in water?
Water is the usual method. Some gardeners ferment in the tomato's own pulp without added water; both work, but the water method makes it easier to pour off the empty seeds.
How do I know which seeds are good?
Good seed sinks. After fermenting, pour off the floating pulp and empty seeds, and keep the ones that settled at the bottom.
Why are my saved seeds mouldy?
Almost always because they were not fully dry before storing. Dry until the seeds snap, and store in a cool, dry place.
Tools for this guide
Related guides
- How to Save Seeds from Cucumbers, Peppers and Squash
- When to Harvest Seeds (and How to Tell They're Ready)
- How to Save Sunflower Seeds
Sources and research notes
This guide describes home seed-saving, not commercial seed production. Fermentation times and storage advice reflect UK horticultural guidance; results vary with variety and climate.
Written and edited by the Seedledge Editorial. Every guide answers one real growing question, is checked against the sources listed above, and is updated when guidance changes. We are an independent editorial desk, not horticultural professionals — read how we research and update our guides.
