How Feminised Seeds Are Really Made (The Full Process)

Watch the episode · 8:07

Every feminised seed starts with a female plant that has been tricked into making pollen. Plant ten regular seeds and about half grow up male. Plant ten feminised seeds and almost all are female. So how do breeders do it? Here is the whole process, step by step, with real photos from the research, plus a discovery from 2026 about what really decides a plant's sex, and the question everyone asks: are these seeds actually any worse?

Source · Header photo: induced male flowers. Flajšman et al., Front. Plant Sci. 2021, CC BY

The short version ▶ 0:36

Spray a female plant with a silver solution and she grows male flowers. Her pollen has no Y chromosome to pass on, so almost every seed it makes comes up female. That is the whole trick. How it really works, and what can go wrong, takes a little longer.

What decides sex? ▶ 0:53

Start with a regular seed. Every seed gets an X chromosome from its mother. From its father, it is a coin toss: an X or a Y. XX makes a female, XY makes a male.

Before going further, here is what to look for. A female flower is a pair of fine white hairs. A male flower is a small green sac that hangs down, then splits open to release pollen.

Source · Richards et al., Plants (2026)

You might assume the Y works like ours: have one, and you are male. But in 2026, in Nature Communications, a large team compared the chromosomes of cannabis and its cousin, hops. They found no clear sex gene on the Y at all. And plants with extra X chromosomes, XXY, commonly make female flowers, Y and all.

So what does decide it? Their best candidate sits on the X: a gene that helps build a plant hormone called ethylene. It is a strong candidate, not the final word. But it would explain a lot, because ethylene is exactly what the feminising trick goes after.

Source · Carey et al., Nature Communications (2026)

Think of ethylene as a signal that says: make female flowers. Silver gets in the way, because it stops the plant sensing that signal. So a genetically female plant starts building male flowers instead. Nothing in her genes has changed. She is still XX.

Source · Richards et al., Plants (2026)

It works the other way too. In a 2026 study, a genetically male plant sprayed with a chemical that releases ethylene grew female flowers beside his male ones.

Source · Garcia-de Heer et al., Plants (2026)

The recipe, step by step ▶ 2:26

This trick is older than you might think. In 1982, researchers put silver compounds on the tips of female cannabis plants, and they grew male flowers. One form, silver thiosulfate, worked best. Forty years on, it is still the standard.

Source · Mohan Ram & Sett (1982)

Step 1: pick the mother. She has to be truly female, and stable, because everything after depends on her. And do it indoors, because stray pollen from outside can ruin the batch.

Source · Timoteo Junior & Oswald, Front. Plant Sci. (2024)

Step 2: spray, usually with silver thiosulfate, over the whole plant, while it is still growing leaves. How many sprays? A 2024 review found one was as good as three for getting male flowers. But flowers are not the same as plenty of good pollen: one 2026 protocol, not yet peer reviewed, needed about ten sprays to get enough. Another 2026 study got the most complete flip by adding a second hormone, gibberellin. And it is harsh: at the strongest dose in one trial, leaves came up in yellow spots.

Source · Flajšman et al. (2021) · Naim-Feil et al., preprint (2026) · Garcia-de Heer et al. (2026)

Step 3: switch the lights to 12 hours, and watch. In these photos from a 2026 study, the red arrows are female flowers and the white arrows are the new male ones. The first male buds showed up under the microscope 7 days after spraying. By day 21, the top of the plant was mostly male flowers.

Source · Judkevich et al., Plants (2026)

Step 4: collect the pollen. This is a pollen sac under an electron microscope, packed with grains. Because the plant is XX, every grain carries an X. There is no Y to pass on. Kept frozen, it stays viable for up to a year, though fresher pollen works better.

Step 5: brush that pollen onto another female, or back onto the same plant. About six weeks later, you have seeds. In one 2026 protocol, not yet peer reviewed, a single pollinated plant typically gave around 1,000.

Source · Naim-Feil et al., preprint (2026)

The maths is simple now. An X from the mother, an X from the pollen. Every seed gets two X chromosomes: female, almost every time.

What can go wrong ▶ 4:34

Plenty. Silver doesn't flip every flower neatly. A microscope study found three outcomes: fertile male flowers, sterile ones with collapsed pollen sacs that never open, and odd mixed flowers. At best, 54% of the pollen was viable.

Source · Judkevich et al., Plants (2026)

And she is a poor stand-in for a real male. In a 2023 study, true males made more than three times as much pollen as treated females. Each flower made about the same amount: the true males just grew far more of them, and flowered for longer.

Source · Wizenberg et al., Plants (2023)

It isn't foolproof, either. In regular vs feminised seeds we met the Montana grower whose feminised seeds came up about 30% male. The likely causes: a mother that wasn't truly female, or stray pollen.

Source · Timoteo Junior & Oswald, Front. Plant Sci. (2024)

Silver thiosulfate isn't the only way. Colloidal silver, the cheaper home version, also works: up to 379 male flowers on a plant in one 2021 trial, though results vary. And there is the old way: stress a female until she makes pollen on her own. In that 2023 study, drought did the job, with pollen as viable as a true male's. But think about what that selects for: a plant that grows male flowers under stress. We found no study testing whether those seeds herm more, but that is the worry.

Source · Flajšman et al. (2021) · Wizenberg et al. (2023)

One warning. The protocol above mixes its silver solution in a fume hood, with protective gear, so this is not a kitchen job. And we found no good study on silver left in treated flowers. So treat a sprayed plant as a pollen donor only, and don't smoke it.

Are they worse? ▶ 6:09

Honestly, it depends how they were made. When a plant pollinates itself, that is inbreeding, and a 2024 review warns it can cost height, size and THC in the next generation. A 2025 study could even spot self-pollinated seeds by their shape, because they varied less.

Source · Timoteo Junior & Oswald (2024) · Torne et al. (2025)

But the real-world results are milder than you would expect. A 2026 Thai study compared self-pollinated plants with crosses of two different plants. Every self-pollinated plant came up female, yield was no different, and THC was no lower. It is one small study on one local variety, though, so don't read too much into it.

A 2020 study of plants that pollinated themselves found much the same: their seeds came up genetically female, with about as much genetic variety as crossed seeds after one generation.

Source · Punja & Holmes, Front. Plant Sci. (2020)

And do feminised seeds herm more? We still found no study comparing them directly with regular seeds. The tendency runs in families, so the mother may matter more than the method.

Source · Richards et al., Plants (2026)

The verdict ▶ 7:13

If you just want flowers, feminised seeds are fine. If you want to breed, you need real males, so grow regular. Read the pack: an S1 means self-pollinated, an F1 means a cross of two parents (what the codes mean). And back breeders who test their mothers.

A feminised seed is a small deception: silver blocks the signal for female flowers, and a plant with no Y to pass on makes the pollen. Selfed seeds may vary less, but they held up in small trials, and stable, tested mothers matter most.

Research photos are used under CC BY licences, cropped, and credited on each image; most plant photos were also upscaled, which can add fine detail that wasn't in the original.