Selfing (S1 Seeds)

What selfing is

Selfing is forcing a female cannabis plant to produce viable pollen, then using that pollen to fertilize a female flower — either on the same plant or on a clone of it. Because cannabis sex is largely determined by XX (female) / XY (male) chromosomes, and a selfed female has no Y chromosome to contribute, every viable seed inherits two X chromosomes and grows into a female plant Strong evidence^[1][2]. These seeds are called S1 (selfed first generation). Subsequent selfings are S2, S3, and so on.

S1 seeds are not clones. Genetically they're the result of a single parent crossed with itself, which is the most extreme form of inbreeding possible in a diploid organism. Any recessive allele the mother carries has a 25% chance of showing up homozygous in each S1 seedling Strong evidence^[3]. That includes desirable traits the mother was hiding and undesirable ones — including the tendency to throw nanners under stress.

Why growers use it

There are three honest reasons to self a plant:

1. Make feminized seed. The commercial seed industry is built on this. S1s of a proven mother give customers a near-100% female germination rate, which beats hunting through regular seed ^[1].
2. Preserve a clone-only cut. If you have a beloved cultivar that exists only as a clone (Chemdog, GSC phenotypes, OG cuts), selfing converts it into seed form that can be stored for years. The seeds won't be identical to the mother, but they'll share her gene pool.
3. Expose recessives for breeding. Breeders self a plant specifically to see what's hiding in the genome — color, terpene, or resistance traits that the heterozygous mother masks.

What selfing does not do: it doesn't boost potency, it doesn't increase yield, and it doesn't 'stabilize' a line in the way that multi-generation inbred line (IBL) breeding does Disputed. Claims that S1s are 'the same as the mom' are marketing folklore Anecdote.

When to start

Start reversal sprays at the beginning of week 2 to week 3 of 12/12 (or when an autoflower is in early flower). The donor plant needs to be in flowering mode so it's producing the hormone signals that respond to silver. Sprays applied during veg are wasted.

Pollen typically becomes mature 3–5 weeks after the first spray. Plan your pollination target (a clone of the same plant, or lower branches of the donor) to be at week 3 of flower when pollen drops, so seeds have 5–7 weeks left to mature before harvest Weak / limited^[4].

How to do it: step-by-step

Materials

• Colloidal silver (CS) at ~30 ppm minimum, or silver thiosulfate (STS) solution. STS is far more effective and only needs one or two applications; CS requires daily spraying Weak / limited^[4][5].
• Spray bottle, gloves, eye protection, mask.
• A dedicated isolation space with its own ventilation. Pollen is microscopic and travels everywhere.

Steps

1. Pick your donor. Choose a plant you actually want to reproduce — vigor, structure, terpene profile, resistance. Health matters: a stressed or sickly donor makes weak seed.
2. Take clones first if you want the seed parent to be separate from the pollen donor. Many breeders reverse one clone (pollen source) and pollinate a second clone (seed bearer) of the same plant. This is still selfing — same genotype.
3. Move the donor into isolation before spraying. Treat it like a quarantine.
4. Begin spraying at week 2–3 of 12/12. For STS: spray the branches you want to reverse once, possibly a second light spray 7 days later. For CS: spray the same branches daily until pollen sacs form, then stop.
5. Stop spraying once sacs are clearly forming (usually 10–14 days in). Continued spraying past this point damages tissue and reduces pollen viability.
6. Wait for sacs to swell and split. This is typically 3–5 weeks after the first spray. You'll see yellow-green pollen.
7. Collect pollen by tapping sacs over wax paper, or let the donor stand next to the seed-bearer plant in the same sealed room.
8. Pollinate at week 2–3 of flower on the seed-bearer. Touch pollen to pistils with a small brush, or shake the donor near target branches.
9. Rinse the room and yourself afterward. Shower, change clothes, wipe surfaces. Pollen contamination of a flower room ruins entire harvests.
10. Harvest seeds 5–7 weeks after pollination, when bracts have swollen and seeds rattle loose or show dark tiger-striping Weak / limited^[4]. Dry and store cool, dark, and sealed.

Never consume buds from the sprayed branches. Silver compounds are not something you want to smoke Strong evidence^[5].

Common mistakes

• Selfing a hermie-prone mom. If the donor throws nanners under stress, her S1s will throw nanners under less stress. Selfing concentrates this trait fast Weak / limited^[3].
• Smoking sprayed buds. Branches treated with CS or STS are contaminated. Label and discard them.
• Pollen contamination. No separate ventilation, no isolation, or shared tools with the main flower room — and suddenly every plant in the house is seeded.
• Spraying too early or too late. Veg-stage sprays do nothing. Sprays past week 4 of flower produce weak or sterile pollen.
• Using weak colloidal silver. Homemade CS under 15 ppm often fails. STS is more reliable but more chemically involved to mix.
• Calling S1s 'clones in seed form.' They aren't. Expect phenotype variation, sometimes substantial.
• Skipping clone backup. If you only have one cut and you reverse the whole plant, you've gambled the genetics on a single seed run.

Related techniques

• Rodelization — letting a female stress herself into producing nanners naturally, then using that pollen. Cheap, but selects for instability Weak / limited.
• STS reversal — the chemical workhorse of the commercial fem-seed industry. More efficient than colloidal silver ^[4][5].
• F1 hybrid breeding — crossing two distinct stable parents instead of selfing one. Produces hybrid vigor; selfing does the opposite.
• Cubing / backcrossing (BX) — repeatedly crossing offspring back to a parent to lock in traits. A slower but more genetically sound way to 'preserve' a mother than selfing.
• IBL (inbred line) breeding — multiple generations of sibling crosses with selection. Produces true stability; S1 alone does not.

See also: Feminized Seeds, Pollen Collection and Storage, Backcrossing.

Sources

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