Seeds: choosing, storing, sowing and saving your own

Every garden starts with a seed, and a hydroponic garden is no exception: a sponge, a rockwool cube, a few seeds, and the tower fills up. But seeds have to be chosen, stored and tested, and you can also save them from your own plants. Here is the complete cycle: choosing the right varieties, keeping them alive, sowing them, then producing your own seeds and sharing your extras on the forum seed swap.

1. Choosing your seeds

Open-pollinated variety or F1 hybrid?

On a seed packet, F1 means a first-generation hybrid: the cross between two parent lines chosen by a breeder. The F1 plant is often vigorous and very uniform. Its seeds, however, mix the traits of both parents: the next generation gives a mix of different plants, usually less interesting than the mother plant.

An open-pollinated variety (or heirloom variety, one that “breeds true”) comes back identical from its seeds, as long as you avoid cross-pollination. It is the mandatory starting point if you want to save your seeds or offer them on the seed swap.

Criteria specific to hydroponics

• A compact habit: cut-and-come-again lettuces, small-leaved basil, dwarf or determinate cherry tomatoes for a tower or a jar.
• Slow bolting for salad greens and cilantro, especially under LEDs or in summer: look for “slow to bolt” or “summer” on the packet.
• Seeds that are easy to handle: pelleted lettuce seeds can be placed one at a time in a sponge; on the other hand, they keep for a shorter time.
• Untreated seeds: some commercial seeds are coated with a colored fungicide. Choose untreated seeds, organic if possible; only these are accepted on the seed swap.

2. Storing your seeds

A seed is alive: it breathes slowly and draws on its reserves. Three enemies speed up its aging: moisture, heat and light. US agricultural extension services sum up the rule this way: each percentage point less moisture in the seed, and each 5 °C (9 °F) lower, roughly doubles its storage life.

• Fully dry: a seed that is ready to store snaps cleanly instead of bending. Recommendations aim for less than 8% moisture.
• In paper envelopes, labeled, stored in an airtight glass jar with a silica gel packet (the kind found in shoe boxes works).
• Cool and dark: a cupboard in an unheated room, or the refrigerator if the jar is truly airtight. Take it out a few hours before opening it, to avoid condensation on the cold seeds.
• Never in the greenhouse, on top of the fridge, near the heater or next to your heated reservoir.

How long do they last?

Approximate, conservative times for good germination, for properly stored seeds (Colorado State University Extension). Many live longer: the germination test settles it.

3. Sowing in hydroponics

Preparing seeds before sowing

• Soaking: large seeds (peas, beans, nasturtium) sprout faster after a few hours in lukewarm water, up to overnight. Not needed for small seeds, which get damaged.
• Scarification: a few seeds with a very hard coat, like nasturtium, come up better if you lightly wear down their coat with a file before soaking, without touching the embryo.
• Pre-sprouting: sprout them on damp paper, then place the already open seed in the cube. Handy for old batches or rare seeds.

At sowing time

The detailed technique (media, moisture, light, transplanting) is in the guide Sowing and transplanting in hydroponics. The essentials, from the seed side:

• A clean, inert medium: a pre-soaked rockwool cube, a coco plug or a horticultural sponge. Never garden soil in a recirculating system.
• Two or three seeds per cube if the batch is old or barely tested, then keep the best seedling.
• Little or no covering for small seeds: lettuce germinates better on the surface, barely covered.
• The right temperature: many lettuces germinate poorly above about 25 °C (77 °F); tomato, pepper and basil, on the contrary, prefer warmth.
• No nutrients at first: the seed has its own reserves. The nutrient solution, diluted, comes in with the first true leaves.
• Staggered sowing: a few seeds every two or three weeks ensure a continuous harvest of salad greens and herbs.

4. Saving your own seeds

Start with the easiest

Self-pollinating species usually pollinate themselves, within their own flower: tomato, lettuce, peas, beans, and largely pepper. Their seeds stay true to the variety without any special precautions. Cross-pollinating species, on the contrary, cross easily with other varieties of the same species, through insects or wind: cucumber, melon, squash, corn, and also basil or arugula. For these, only one variety in flower at a time, or hand pollination under a row cover.

Choosing seed plants

Mark the best plants with a tie or a label: healthy, vigorous, true to the variety and, for salad greens, the last ones to bolt. If you save seed from the first lettuce that bolts, you are selecting for exactly that: fast bolting. If possible, use several plants to keep some diversity.

Species by species

5. Labeling: the batch’s memory

An unlabeled envelope is a lost envelope. Write down at least:

• the species and variety;
• the year and place of harvest, and the growing system (tower, Kratky, NFT);
• the germination rate and the test date;
• the original source (seed company, seed swap member) and your notes: earliness, taste, resistance to bolting.

This is also what community seed swaps and seed libraries ask for, like those of Nature & Progrès in Belgium: a well-described, tested batch, grown by the donor.

6. What the regulations say

• In France, the Ministry of Agriculture points out that home gardeners may swap seeds of non-protected varieties for free. The vegetables harvested can be eaten or sold freely. Since the law of June 10, 2020, seeds of public-domain varieties may also be sold to non-professional users, which secured the activity of nonprofit associations.
• In Belgium, seed libraries and swaps between individuals take place freely as long as nothing is sold; marketing seeds is subject, as everywhere in the European Union, to specific rules.
• Varieties protected by a plant variety right (COV, the EU and French equivalent of plant variety protection) remain so for 25 or 30 years depending on the species: do not multiply them for distribution without the breeder’s consent. Most heirloom and open-pollinated varieties are free.
• From outside the European Union, bringing seeds in requires a phytosanitary certificate: no mailing of seed packets between individuals from or to a non-EU country.

These pointers summarize official texts and are not legal advice; if in doubt, check with the plant health authority in your country.

7. Sharing: the seed swap

A tomato gives hundreds of seeds, a lettuce gone to seed thousands: far more than a tower can hold. The forum seed swap is made for these extras.

• Giving, looking for or swapping: each listing states the species, variety, harvest year, germination rate, quantity and how it will be handed over.
• Reading is open to all; to post, reply or contact a member, you just need to be logged in.
• The “Contact” button sends an email to the member: postal addresses are never written on the forum.
• The rules are simple: open-pollinated varieties, untreated seeds, healthy plants, free gifts and swaps (shipping costs can be shared).

Offer my seeds See the listings