How to preserve your seeds from one year to the next?

Harvesting your own seeds closes the garden loop: no need to buy them again every spring, and above all, your varieties adapt year after year to your soil, climate, and way of growing. But between harvest and the next sowing, eight to ten months pass during which the seed is alive and fragile. That is when everything is decided.

This guide covers the six steps between a harvested seed and one that will truly germinate: choosing the right seed plant, harvesting at the right stage, cleaning, drying, storing, and checking.

First of all: a reproducible seed

A prerequisite that determines everything else: only reproducible seeds (open-pollinated varieties, heirloom varieties, farm-saved seeds) produce true-to-type offspring. F1 hybrids segregate from the second generation onward—you will indeed harvest seeds, but the resulting plants will be variable and often disappointing.

We explain this distinction in detail in What is the difference between F1, hybrid, and reproducible seeds?. Our entire catalog consists of heirloom and reproducible varieties.

1. Choose your seed plant

The quality of your future harvests is decided here, long before the seeds are harvested. A seed plant is the plant or plants you deliberately allow to go to seed.

Select the right plants

• Keep the most vigorous and healthiest plants, never those that performed poorly or were diseased.
• Select for the trait that interests you: earliness, drought resistance, flavor, compact growth…
• For leafy vegetables, avoid keeping plants that bolt first: you would unknowingly select a variety that bolts quickly.

Keep enough plants

This is the point most often overlooked. Some species self-pollinate and tolerate a single seed plant very well; others are cross-pollinating and lose vigor if you start with too small a population.

Avoid unwanted cross-pollination

Two varieties of the same species planted side by side will cross. The most common cases in the vegetable garden:

• Squashes: varieties of the same botanical species cross with one another. A Butternut and a Musquée de Provence (both Cucurbita moschata) will cross; a Butternut and a kabocha squash (Cucurbita maxima) will not.
• Cabbages: cauliflower, broccoli, kale, and Brussels sprouts belong to the same species (Brassica oleracea) and cross with one another.
• Beets and Swiss chard: same species, crossing guaranteed.

Two simple solutions: keep only one variety per species for seed production each year, or space seed plants widely apart. For self-pollinating species such as tomatoes, a few meters are usually enough.

2. Harvest at the right time

A seed harvested too early has not completed its maturation and will not germinate, or will germinate poorly. The general rule is: harvest well past the eating stage.

Dry seeds

• Peas, beans, broad beans: wait until the pods are brown, dry, and crackly on the plant.
• Lettuce: harvest when about half of the fluffy seed heads have opened, shaking the stem over a bag.
• Carrot, parsley, dill, coriander, fennel: harvest the umbels when they turn brown, before they fall apart on their own.
• Flowers (marigolds, borage, nasturtiums, cosmos): harvest the dry flower heads in dry weather, late in the morning.

Wet seeds

• Tomato: fully ripe, or even slightly overripe.
• Bell pepper, chili pepper: wait until the final color develops and the fruit is slightly wrinkled.
• Cucumber: well past the eating stage, when the fruit turns yellow-orange and hardens.
• Squash, pumpkin: harvest at the usual stage, but ideally let the fruit dry off for a few weeks before opening.
• Eggplant: the fruit should be yellowish or brownish and hard — inedible, in other words.

3. Clean and sort

Fermenting tomato seeds

This is the specific step for tomatoes, and it is not optional. Each seed is surrounded by a gelatinous coating containing germination inhibitors. Fermentation dissolves it and also removes some bacteria transmissible through the seed.

1. Press the seeds and their juice into a small glass jar with a little water at the bottom.
2. Leave at room temperature for 2 to 4 days, without sealing airtight. A whitish film forms on the surface: this is normal.
3. Fill the container with clear water and stir. Viable seeds sink to the bottom, while debris and empty seeds float: remove the surface water.
4. Repeat until the water is clear, then drain through a fine sieve.

Other species

• Squash, cucumbers, and melons: extract the seeds, rub them by hand under water to remove the pulp, and discard any seeds that float.
• Bell peppers and chili peppers: simply detach the seeds from the placenta without washing. Gloves are recommended for hot peppers.
• Dry seeds: rub the pods in a salad bowl, then winnow — blow gently or pour from one container to another in front of a fan: the light debris blows away while the seeds remain.

Systematically discard seeds that are flat, discolored, pierced, or abnormally small.

4. Drying — the stage where the most batches are lost

A poorly dried seed becomes moldy or continues to “breathe” and is depleted within a few months. A properly dried seed enters deep dormancy and can be stored for years.

• Spread in a single layer on a plate, sieve, or kraft paper. Avoid paper towels, to which small seeds stick permanently.
• Never use newspaper: the inks may migrate.
• Dry in the shade, in a well-ventilated room, between 20 and 25 °C. Never in direct sunlight, in an oven, or on a radiator: above approximately 35 °C, the embryo is damaged.
• Allow 1 to 3 weeks depending on the seed size and ambient humidity. Stir every two or three days.

5. Storage: dry, dark, cool, stable

The three enemies of stored seeds are moisture, heat, and light — in that order of importance.

Containers

• Kraft envelopes or bags: the classic choice. They allow air circulation and are ideal if your seeds are perfectly dry and the room is suitable.
• Glass jars with rubber seals: the best option in a cellar or damp room, provided the seeds are completely dry. Add a sachet of silica gel or a spoonful of uncooked rice wrapped in a piece of cloth.
• Metal tins: good protection against rodents and insects.

Where to store them

An entryway cupboard, an unheated hallway, or a dry attic. Avoid: the kitchen (steam), the bathroom, the conservatory (temperature fluctuations), and an uninsulated garage.

The refrigerator significantly extends their lifespan, but only in a perfectly dry, airtight container. Take the jar out and let it return to room temperature before opening it; otherwise, condensation will settle directly on the seeds.

Labeling

Without exception, write on each packet: the species and the exact variety name, the harvest year, and, if possible, a note about the plant’s performance (early, drought-resistant, highly productive…). These notes, accumulated over several years, are worth far more than the seeds themselves: they are your breeding record.

6. How long do they keep?

These timeframes assume proper storage. They indicate the period during which the germination rate remains satisfactory, not the date when the seeds suddenly die.

Records reported in horticultural literature far exceed these figures for well-preserved cucurbits. Conversely, seeds from umbellifers and alliums lose their germination capacity very quickly: it is better to replace them every year.

In our shop Seed Collection — Specially for Beginner Gardeners 10 open-pollinated varieties, wooden labels included · €34.90

The germination test

Five minutes of work that can prevent an empty bed in spring. Carry this out 2 to 3 weeks before the planned sowing date.

1. Count 10 seeds (or 20 for a more reliable result) selected at random from the batch.
2. Place them between two sheets of moistened paper towel in a closed container.
3. Place at room temperature, around 20 °C, away from direct sunlight. Check the moisture every two days.
4. Count the germinated seeds: 5 to 7 days for a radish or lettuce, 10 to 14 days for a tomato, and up to 3 weeks for parsley.

Building your seed library

• Sort by botanical family rather than alphabetically: this helps you plan rotations and assess crossbreeding risks.
• Date everything, and put the oldest batches at the front: they get used first.
• Don't keep everything. A seven-year-old batch from which you have never sown a single seed isn't worth the space it takes up.
• Exchange them. Seed swaps, seed libraries in municipal libraries, and gardener networks are the best way to introduce new genetic material into cross-pollinating species and discover local varieties.

Frequently asked questions

Can seeds bought in packets be sown the following year?

Yes, without difficulty, as long as the packet has been resealed and stored in a dry place. The durations above also apply to commercially purchased seeds, starting from their harvest year — not the purchase date.

Should I freeze my seeds?

Freezing is used in professional seed banks, but it requires a very low residual moisture level, impossible to guarantee with home drying. A seed that is still slightly damp will be destroyed by the formation of ice crystals. For a gardener, the best compromise is an airtight jar in the refrigerator.

What should I do with floating seeds?

When washing wet seeds, those that float to the surface are generally empty or poorly formed: discard them. This test does not apply to dry seeds, which almost all float.

Why are my squash seeds producing strange-looking fruits?

This indicates cross-pollination the previous year with another variety of the same botanical species, or with a neighboring ornamental squash. The resulting fruits can sometimes be bitter and toxic: refer to the warning at the beginning of the article.

Does an old seed germinate less well?

The germination rate gradually declines and emergence becomes less uniform: aging seeds germinate more slowly and less regularly, even when the final percentage remains acceptable. Hence the value of a preliminary test.

Key points

Storing your seeds requires neither equipment nor technical expertise — only diligence. The rest is a pleasure: sowing, every spring, seeds from your own garden.

To take it further

• Why choose non-hybrid, open-pollinated seeds?
• Heirloom seeds: what are they? Why grow them?
• The month-by-month sowing calendar
• Cold stratification: why and how to germinate seeds?
• How do you sow seeds in cotton, pots, or directly in the ground?

To start your first collection, explore our open-pollinated heirloom varieties, our vegetable seeds, and our seed collections — all our seeds can be harvested and replanted from one year to the next.