Harvesting and storing seeds from your own plants

Why harvest your own seeds?

A seed you harvest yourself costs nothing, while the same variety in a shop packet costs roughly two to four euros. Harvest your own and you also get exactly the same plant back: the same flower colour, the same height, the same taste in vegetables. That makes your garden more sustainable, without buying new packets every year.

Many varieties give true seed year after year, as long as you get three things right: harvest at the right moment, dry the seed thoroughly, and store it cool and dry. This article shows you which varieties stay true, how to harvest and dry seed, how to store it for years, and how a simple germination test tells you whether old seed is still good.

Which varieties breed true?

Not every plant gives seed that comes back exactly the same. Open-pollinated varieties, especially vegetables and wild flowers, almost always come true. Hybrid varieties, often marked F1 on the packet, can turn out very different next year.

Tomato (Solanum lycopersicum): comes back very true. The seed sits in a gel inside the fruit; yellow seed is riper than seed that is still white.

Bean (Phaseolus vulgaris) and pea: very easy and true. Let the pods dry on the plant, then take the seed out.

Carrot (Daucus carota), radish and beetroot: true, but carrot and beet are biennial. In the first year the plant only forms a root; it only flowers and sets seed in the second year. Radish flowers already in its first year, so you harvest its seed the same autumn.

Lettuce (Lactuca sativa) and spinach: very true. Spinach often self-seeds; you just need to collect seed for next year.

Courgette and pumpkin (Cucurbita pepo): true, but they set no fruit without pollination. Help the bees along by hand-pollinating if you want to be sure.

Cosmos (Cosmos bipinnatus), zinnia and calendula (pot marigold): very true, the seed ripens visibly and drops loose easily.

Nigella (love-in-a-mist): very easy to harvest; the seed pods are large and easy to spot.

Poppy (field poppy, Papaver rhoeas): true, the seed sits in a pod that you let dry and then shake out.

Lavender (Lavandula angustifolia): the seed is small but visible; let it dry on the plant.

Marjoram and oregano: give fine but true seed.

Dahlia: does not give true seed; these are hybrids with unpredictable offspring.

Rose: most modern garden roses are hybrids and unreliable; older, species roses often do give true seed.

Many perennials, such as hydrangea and aster, hybridise easily, and seed from F1 hybrids always gives a different result too. For those, it is better to buy fresh each season, or to propagate perennials by cuttings or division instead.

When exactly is the seed ripe?

Harvest too early and the seed germinates poorly. Harvest too late and birds eat it, or it falls into the grass.

Tomato: wait until the fruit feels soft and is fully yellow, orange or red; the seed is ripe once it comes out of the flesh easily.

Bean: the pods turn paper thin and rattle clearly; harvest once they are completely brown and dry, usually in September.

Carrot and beet: the flower heads turn brown and the seed falls into your hand at the slightest touch.

Lettuce and spinach: the seed appears as small brown teeth; you can cut the whole flower stem and let it finish drying at home.

Cosmos and zinnia: the seed turns black brown and dry and drops loose from the flower head.

Nigella: the seed pod turns brown and papery; you can pick it off whole.

Poppy: the seed pod turns grey and dry; shake it empty over a bowl.

Lavender: the flowers dry on the plant; the seed sits between the bracts.

How do you harvest the seed?

For tomatoes, cut the fruit open and scrape the seed and gel into a bowl. Let it ferment for a day so the gel breaks down, then rinse it clean through a fine sieve and leave it to dry. Beans are the easiest: once the pods are fully brown and dry, usually in September, pick them and put them in a paper bag; two weeks later they open on their own, so you can shake the seed loose. For carrot, beet and lettuce, cut the whole flower stem and hang it upside down over a box or on newspaper; the seed drops out by itself within about two weeks.

For flowers, roll cosmos seed loose between your fingers straight into a bowl. Nigella pods are large and simply pulled off one by one. Shake dry poppy pods into a paper bag until all the seed falls out. For lavender, cut the whole flower spike, dry it on newspaper, and shake the seed free after roughly two weeks. Not sure which of these seed-saving plants combine well in your own border? At gardenworld.app you can see them first in a preview of your own garden.

Drying: the step that decides everything

Wet seed goes mouldy, dry seed stays good for years. This is the most important step of the whole process.

Spread the seed loosely on clean paper towel or newspaper, never in a heap. Keep it somewhere without direct sun, since UV breaks down the oils in the seed, and choose a dry spot with some air movement: a dry shed, an attic or an airing cupboard all work well. Leave it for two to three weeks and stir it now and then so it dries evenly. It is ready once the seed snaps instead of bending when you pinch it.

For very fine seed, such as lavender or poppy, the rice method helps: dry the seed briefly on paper first, then put it together with uncooked rice in a sealed jar. The rice pulls out the last of the moisture, and after about two weeks you take the seed out again and store it separately. Never store seed in plastic, since moisture gets trapped inside and causes mould; paper, cotton or glass are all safe.

How do you store seed for years?

Seed keeps longest cool, dark and dry. The fridge is the best spot; only use the freezer once the seed is bone dry.

Write the plant name, variety and harvest year on each paper envelope in pencil, since ink fades faster. Put the envelopes in a closed box on the bottom shelf of the fridge, not in the door, where the temperature fluctuates most. Stored this way, seed easily stays good for three to five years. A sealed glass jar on a cool shelf away from the kitchen also works for years. Avoid a sunny windowsill, a damp cellar or a heated room: all of these shorten how long the seed stays viable.

Germination test: is old seed still good?

After a year or two you will want to know whether stored seed still germinates. Lay a few seeds on a damp paper towel, roll it up and put it in a plastic bag. Keep the bag somewhere warm, around 20 to 22 degrees, and after a week count how many seeds have sprouted. For tomatoes, 90 percent germination is normal; for lavender, 60 percent is already fine, since it germinates slowly. If fewer than half germinate, the seed is probably too old, and you are better off looking for fresher seed of the same plant or buying new.

Step by step

Step 1: Choose which plants to let grow on

Let the fruit or flower on a few healthy plants stay in place instead of harvesting or cutting it. Watch for the ripening moment: beans, tomatoes and cosmos all show it clearly once the seed feels brown, papery and dry.

Step 2: Harvest the seed

For vegetables, cut or pick the ripe fruit or pod and remove the seed; for flowers, pick the seed pod or roll the seed loose with your fingers. Collect everything in a paper bag or a bowl.

Step 3: Clean the seed

Sift large seed, such as poppy and nigella, by hand yourself. Shake very fine seed, such as lavender, through a fine sieve so chaff and husks fall away.

Step 4: Let it dry properly

Two to three weeks on paper, out of the sun, stirring occasionally. The seed is ready once it snaps instead of bending.

Step 5: Store it

Fill a paper envelope or a glass jar, label it with the plant, variety and year, and put it on the bottom shelf of the fridge until you sow it again next spring.

Frequently asked questions

Why does seed from my fruit tree not work? Fruit trees are usually grafted onto a different rootstock, or they are themselves a hybrid variety. Seed from the fruit grows into a different, often less tasty tree. Only seed from truly wild species reliably comes true.

Can I save seed from shop-bought plants? Almost never. Most potted plants and summer bedding from the garden centre are F1 hybrids, so next year's seed turns out quite different. For those varieties, it is better to buy fresh plants each season.

How long does seed usually last? That depends on the species: tomato stays good for about 4 to 6 years, bean for 3 to 4 years, and lavender for 2 to 3 years. Carrot and onion lose viability faster, while pumpkin and beet last longer. The riper and drier the seed was at harvest, the longer it keeps.

Can I store seed in the freezer? Yes, but only once the seed is completely bone dry. If it is not, ice forms inside the seed and kills it. Use a desiccant such as silica gel to be safe, and only try this once you already have some experience with drying seed.

See it in your own garden first

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