How to Save Tomato Seeds: Fermenting, Drying & Storing Seed from Your Best Plants

Somewhere on the plant this week is the best tomato you grew all year — the one that ripened first, tasted sweetest or simply never got blight when its neighbours did. Eat it, by all means, but scoop the seeds out first. Tomatoes are the easiest vegetable of all to save seed from: the flowers pollinate themselves before they even open, one fruit holds more seed than a bought packet, and a properly dried batch stays viable for five years or more. There is one step most people skip, and it is the one that matters — a short ferment in a jar on the windowsill that cleans the seed, strips off the gel that stops it germinating, and makes the difference between a tin of seed that grows and a tin that sulks. Here is how to save tomato seeds, which varieties are worth the trouble, and how to keep them until sowing time in February.

• Save from Open-pollinated and heirloom varieties · fully ripe fruit · clean, healthy plants
• Ferment 2–3 days at 20–25 °C · stop when a film forms and the good seed sinks
• Dry 1–2 weeks on a china plate or coffee filter · room temperature, never above 35 °C
• Keeps 4–6 years cool, dark and dry — often longer · test ten seeds each spring

Which tomatoes come true from saved seed

The first question is not how, but whether. Seed from an open-pollinated variety — every heirloom, and most of the old reliables — grows into the same tomato next year. Seed from an F1 hybrid germinates perfectly well but does not come true: the seedlings split back into a jumble of the two parent lines, so you might get something good, something odd, or six plants that are all different. The packet tells you which is which, and so does the name. In our range, Gardener's Delight, Marmande, San Marzano, Black Cherry, Black Krim, Brandywine, Coeur de Boeuf, Costoluto Fiorentino and Green Zebra all come true; anything with F1 after it — Supersweet 100 F1, Dattolime F1, Gourmansun F1 — is for eating, not for saving. Our guide to heirloom, F1 and organic seed explains the breeding behind that, and seed packets and terms decodes the labels.

The second question is crossing, and here tomatoes are unusually kind. The stamens of a tomato flower are fused into a cone around the stigma, and pollination happens inside that cone before the petals open, so bees rarely get a look in — cross-pollination between neighbouring varieties is usually below five per cent. The exceptions are the big-flowered beefsteaks, the potato-leaved types such as Brandywine and the tiny currant tomatoes, whose stigmas can poke out beyond the cone. If you grow one of those next to another variety and want the seed pure, pick fruit from the middle of the plant rather than the first truss, or slip a square of fleece over a truss before its flowers open and take your seed from that. For a cherry or a plum tomato in an ordinary garden, none of this is necessary.

Choosing the fruit — and the plant

Save from the plant, not the fruit. A single spectacular tomato on a mediocre plant tells you nothing; a plant that cropped early, stayed healthy and tasted right is what you want to repeat, so mark it with a length of wool in August and take two or three typical fruits from it now. Let them go fully ripe, even slightly over — the seed inside is mature well before the skin colours, so a fruit that turned red indoors on the windowsill is fine, as our guide to ripening green tomatoes explains; a small, hard, green one is not. Only save from clean plants. Blight is not carried inside the seed, but bacterial canker, speck and several viruses are, and fermentation tames the first two without touching the last. A plant with mottled, distorted foliage is a plant whose seed goes in the bin. Two or three fruits are plenty: a beefsteak holds a couple of hundred seeds, a cherry tomato fifty or so, and either is more than you will sow in three springs.

How to save tomato seeds, step by step

1. Cut across the equator and scoop Halve the fruit around its middle, not from stem to tip, so every seed cavity is open. Squeeze or spoon the seeds and their jelly into a jam jar — one variety per jar, labelled before you do anything else. The flesh is still perfectly good to eat.
2. Ferment for two to three days Add a splash of water if the pulp is thick, cover the jar with a cloth or a loose lid, and leave it at room temperature out of direct sun. Stir once a day. By day two it smells sour and a white or grey film has spread across the top: that is yeast and bacteria digesting the gel, and it is exactly what you want.
3. Stop on time When the film covers the surface and the good seed has sunk to the bottom, the job is done — two days in a warm kitchen, three or four in a cool one. Leave it a week and the seed starts to germinate in the jar; sprouted seed is lost seed.
4. Rinse until clean Pour off the film, the floating seeds and the pulp, top up with water, swirl, pour off again, and repeat until the water runs clear. Tip the seed into a fine sieve under the tap and rub it gently with your fingers to loosen the last of the gel.
5. Dry slowly, on something it cannot stick to Spread the seed in a single layer on a china plate, a ceramic tile or a paper coffee filter — never kitchen roll, which becomes part of the seed. Somewhere airy at room temperature, out of the sun, for a week or two, breaking up the clumps with a finger every day. It is dry when the seeds no longer cling to each other and feel papery rather than leathery.
6. Envelope, label, tin A paper envelope marked with the variety and the year, inside an airtight jar or tin in a cool, dark cupboard — with a sachet of silica gel if you have one. Our seed storage guide covers the details, and a ten-seed germination test on damp kitchen paper in January tells you how thickly to sow.

Why the ferment works

Each tomato seed sits in a sac of jelly, and that jelly is there for a reason: it is loaded with sugars and germination inhibitors that stop the seed sprouting inside a ripe, wet fruit. In nature the fruit falls, rots, and the microbes that rot it dissolve the gel — which is the signal that the seed is free to grow the following spring. The jar on your windowsill simply recreates that rotting in miniature. Yeasts and lactic bacteria break the gel down, the mixture turns acidic, and that acidity, along with the competition, kills the bacteria responsible for canker and speck that ride on the seed coat. Seed that has been through the ferment germinates faster and more evenly, and any that were not going to germinate anyway float to the top and pour away with the scum. The same wet method suits cucumbers and, from a fruit left to go over-ripe, aubergines; peppers and chillies are the opposite case — their seed is scraped out of a fully coloured fruit and dried straight away, no jar required, and the plants themselves can be kept going too, as our guide to overwintering chilli plants explains.

The full ferment vs the quick rinse

There is an even lazier folk method — smear the seeds and jelly straight onto a piece of paper, let it dry, and in spring tear off squares of paper with a seed on each and plant them. It works, after a fashion, for a handful of seed from a plant you trust. For anything you want to rely on, ferment. Whichever route you take, sow the seed as you would any bought packet: under cover from late February at 18–21 °C, as set out in our guide to seed starting indoors, hardened off in May and planted out after the last frost.

Common tomato seed-saving mistakes

• Saving from an F1 — the seed grows, the tomato does not repeat. Check the packet before you bother.
• Fermenting too long — a jar forgotten for a week on a warm windowsill is a jar of sprouted, useless seed. Two to three days, then rinse.
• Drying on kitchen roll in the sun — the seed glues itself to the paper and the heat cooks the embryo. China plate, shade, patience.
• Packing while still leathery — a slightly damp batch moulds the whole tin. If the seeds bend rather than snap, give them another week.
• Saving from the odd one out — the single giant fruit on a plant of small ones is a fluke, not a strain. Save from typical fruit on the best plant.
• Saving from a sick plant — canker, speck and viruses travel on seed. Mottled leaves mean no seed from that plant, however good the fruit.
• Mixing varieties in a jar — tomato seed all looks the same. One variety per jar, labelled before you scoop.

Frequently asked questions

Do I have to ferment tomato seeds?
Strictly, no. Seed rubbed clean through a sieve and dried on a plate will germinate, and for a few seeds of a favourite plant that is a perfectly good method. Fermentation earns its place when the seed has to last — it removes the gel completely, cleans off two of the commonest seed-borne diseases and gives faster, more even germination. Three days of a faintly sour jar is a small price for seed that will still be reliable in five years.

Can I save seeds from supermarket tomatoes?
You can, and they will usually grow — but most supermarket tomatoes are F1 hybrids bred for heated glasshouses and long transport, so the seedlings vary and rarely suit an outdoor garden. Treat it as an experiment rather than a plan. If you want a variety to keep, start from an open-pollinated packet: our tomato seed collection has plenty — browse it by species under Solanum lycopersicum — and the organic tomatoes are mostly open-pollinated too.

How long do saved tomato seeds last?
Four to six years in a cool, dark, dry cupboard, and ten or more in an airtight jar in the fridge with a silica sachet. Germination falls slowly rather than suddenly, so old seed is sown a little thicker, not thrown away. How long seeds last gives the figures for every crop, and a January test on damp paper settles it for any batch you are unsure of.

Can I save seed from the green tomatoes left at the end of the season?
Yes, provided they are full-sized. The seed in a mature green fruit is already viable, so bring the fruit indoors, let it ripen on a windowsill or in a drawer with a banana, and scoop the seed once it has coloured. Small, hard, immature fruits will not ripen properly and their seed is not worth saving. The same trick rescues the last of the crop for eating, and our guide to ripening green tomatoes covers it in full.

A jam jar, three days and a china plate turn this year's best tomato into next year's plants, for nothing. While the jar is fermenting on the windowsill, there is still time to put something in the ground outside: our new guide to growing Swiss chard from seed covers the September sowing that gives you the first greens of spring, and the September sowing list has the rest. Come February, sow your saved seed alongside something new from the cherry tomatoes, the organic range or the full tomato collection — the seeds to sow in February collection shows what else starts then — and keep the rest of our growing guides, the vegetable sowing calendar and the full vegetable seed range to hand for the season ahead.