# Feminised seed and sex reversal: methods, with safety notes

> Feminised seed is made by forcing a genetic female to grow male flowers, then using that pollen on another (or the same) female. Silver ions block ethylene action; silver thiosulfate (STS) sprayed at about 3 mM silver was the most effective treatment in a controlled hemp study, and colloidal silver also works. Silver compounds are hazardous: wear gloves and eye protection, never consume treated plants, and dispose of waste as hazardous. Careless feminising (unproven donors, stress-herm pollen) is a main source of herm-prone seed; reverse only females proven stable over at least two runs.

- Canonical: https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.html
- Category: Breeding · Level: Breeder
- Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Transition, Flower · Systems: Any system
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**How are feminised seeds made?** Feminised cannabis seeds are made by spraying a genetic female, or one branch, with silver thiosulfate or colloidal silver before and into early flower. Silver blocks ethylene, so the plant grows [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) that shed fertile pollen carrying only X [chromosomes](https://genetixbay.com/knowledge/glossary/chromosome.md). That pollen fertilises an untreated female, and nearly all the resulting seeds are female.

**How do I make silver thiosulfate for reversing cannabis?** For 1 litre of about 3 mM silver STS at a 1:4 molar ratio, dissolve 0.51 g silver nitrate in 500 mL distilled water and 2.98 g sodium thiosulfate pentahydrate in another 500 mL. Pour the silver solution slowly into the thiosulfate while stirring; it should stay clear. Use gloves, goggles and a respirator, and dispose of waste as hazardous.

**Colloidal silver or STS for feminised seeds?** STS is the more effective choice for feminised cannabis seed: a 3 mM silver thiosulfate spray applied three times, a week apart, worked best on all four [hemp cultivars](https://genetixbay.com/knowledge/glossary/hemp.md) tested. Colloidal silver also produces fertile pollen but is less potent per spray and needs repeated, often daily, applications. Both are silver hazards; [gibberellic acid](https://genetixbay.com/knowledge/glossary/gibberellin.md) is less consistent.

**When should I spray STS?** Spray STS on cannabis to runoff three times, 7 days apart, starting a few days before or at the [flip to 12/12](https://genetixbay.com/knowledge/glossary/12-12.md), which is grower practice. Spraying too late fails because existing [female flowers](https://genetixbay.com/knowledge/glossary/pistillate-flower.md) won't convert. Male flowers usually appear about 2-3 weeks after the flip and open about 4-6 weeks after it.

**Is reversed pollen safe? Can I smoke a reversed plant?** Never smoke or consume a cannabis plant treated with silver, because silver accumulates in its tissue; destroy it once its pollen is collected. The pollen itself is used only to make seed, and the plants grown from that seed are never sprayed. Handle silver nitrate as a corrosive chemical and dispose of treated material as hazardous waste.

**Why do some feminised seeds turn out [hermaphrodite](https://genetixbay.com/knowledge/glossary/hermaphrodite.md)?** Feminised seeds turn out hermaphrodite mainly because of careless feminising, the GenetixBay breeder position. Reversing a female that wasn't proven sex-stable, or using pollen from a plant that hermed under stress, passes that intersex tendency into every seed. Reverse only females that ran fully female for at least two cycles, and grow out every batch to record its [herm rate](https://genetixbay.com/knowledge/glossary/herm-threshold.md).

**Short answer.** Spray a genetic female (or one branch of it) with silver thiosulfate or colloidal silver before and into early flower; it grows male flowers that shed fertile pollen. That pollen carries only X chromosomes, so seeds it makes are nearly all female [2][4]. Lubell and Brand found 3 mM STS, sprayed to runoff three times a week apart, the most effective treatment on four hemp cultivars [1]. Treat silver compounds as hazardous chemicals. Feminised seed is only as stable as the donor you reverse: careless feminising is one of the main ways [herm-prone](https://genetixbay.com/knowledge/glossary/herm-prone.md) lines reach growers.

> **Breeder's standard.** Reverse only a female that has run fully female for at least two cycles under normal conditions, using controlled reversal, never pollen from a plant that hermed by itself. Grow out a sample of every batch, cull and record intersex plants, disclose the herm rate, and don't release a batch from a line that herms. See [diagnosing hermaphrodites](https://genetixbay.com/knowledge/diagnosis/hermaphrodites.md).

**Legal first.** Making seed may need a licence where you live, and chemical use on plants can be regulated. Check local rules.

## What's happening

Ethylene promotes female flower development in cannabis. Silver ions (Ag⁺) block ethylene receptors, so new flowers develop as male [3]. Silver thiosulfate (STS) carries silver into the plant more effectively than silver nitrate, which is why STS outperformed silver nitrate in early work [3]. Gibberellic acid can also induce male flowers but is less consistent (*Supported*) [2].

The plant is still genetically XX. Its pollen is X-bearing, so any seed is XX (female), barring rare exceptions [4].

## Method comparison

| Method | Typical use | Effectiveness | Notes |
|---|---|---|---|
| STS [foliar spray](https://genetixbay.com/knowledge/glossary/foliar-feeding.md) | 3 mM silver, 1:4 silver nitrate:sodium thiosulfate (molar) [1] | High; 3 mM best for all four cultivars tested, 0.3 mM variable [1] | Industry standard; hazardous chemicals |
| Colloidal silver spray | Repeated sprays, often daily | Effective; up to 379 male flowers per plant in [2] | Less potent per spray, more applications; still a silver hazard |
| Gibberellic acid (GA3) | Spray | Lower and inconsistent [2] | Not recommended as primary method |
| Stress-induced "rodelization" (letting a female self late in flower) | None | Unreliable | Selects directly for intersex tendency; never use for seed lines |

## Preparing STS (illustrative, matches the published ratio)

To make **1 L** of approximately **3 mM silver** STS at a **1:4 molar ratio** [1][5]:

| Component | Amount | Notes |
|---|---|---|
| Silver nitrate (AgNO₃, 169.87 g/mol) | 0.51 g (3 mmol) | Dissolve in 500 mL distilled water |
| Sodium thiosulfate pentahydrate (Na₂S₂O₃·5H₂O, 248.18 g/mol) | 2.98 g (12 mmol) | Dissolve in 500 mL distilled water. If anhydrous (158.11 g/mol): 1.90 g |
| Mixing | Pour the silver nitrate solution **slowly into** the thiosulfate solution while stirring | Reverse order can precipitate silver; a clear solution is correct |
| Wetting agent | A few drops of non-ionic surfactant per litre | Optional | Use distilled or RO water only; [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) chlorides precipitate silver. Make fresh; store any stock in a dark bottle in a fridge and use within weeks (*Grower practice*).

## Step by step

1. **Choose the donor female.** Stable across at least two runs: no intersex flowers. Take a clone and reverse the clone (or one branch), not your only mother.
2. **Separate it.** Move it to a separate space once treated; it will shed pollen.
3. **Spray** to runoff (about 20 mL per small plant in [1]) on three occasions, 7 days apart. Growers commonly start a few days before or at the flip to 12/12 (*Grower practice*). Cover the medium to limit runoff into the pot.
4. **Wait.** Male flowers usually appear about 2-3 weeks after flip and open about 4-6 weeks after flip (*Grower practice*).
5. **Collect pollen** on paper under still air, sieve and use or store (see [pollen collection](https://genetixbay.com/knowledge/breeding/pollen-collection-storage.md)).
6. **Pollinate** an untreated female (for a feminised cross) or a clone of the same plant (for an S1).
7. **Destroy** the treated plant after pollen collection.
8. **Record** the batch as feminised in the GB-BAT and note the reversal method.

## Safety (read this before buying anything)

- **Silver nitrate is corrosive and an oxidiser.** It causes serious eye damage and stains skin black-grey. Wear nitrile gloves, wrap-around goggles and long sleeves. Work away from food. Keep away from children and pets.
- **Spraying makes an inhalable mist.** Wear at least a particulate respirator (FFP2/N95 or better) and spray in a ventilated area away from other plants.
- **Never consume** flowers, leaves or extracts from a treated plant. Silver accumulates.
- **Disposal.** Silver compounds are toxic to aquatic life. Do not pour leftovers or runoff down the drain or onto soil. Collect waste in a labelled container and take it to a hazardous waste facility, following local rules.
- **First aid.** Eyes: rinse with water for at least 15 minutes and seek medical help. Skin: wash with soap and water.
- Read and keep the supplier's safety data sheet (SDS).

## Common mistakes

- Reversing a plant that already hermaphrodites. You'll sell that tendency in every pack.
- Collecting "free" pollen from a stress herm instead of a controlled reversal. That is the [pollen-chucker](https://genetixbay.com/knowledge/glossary/pollen-chucker.md) route to unstable feminised lines.
- Releasing a feminised batch without a grow-out and a recorded herm rate.
- Spraying too late in flower. Existing female flowers won't convert.
- Tap water in the mix: cloudy solution, weak effect.
- Labelling feminised seed as regular, or vice versa. DNA sex markers can check a sample of seedlings [6].

## Evidence

- STS induction of fertile male flowers, 3 mM most effective: *Established* (controlled studies) [1][3].
- Colloidal silver and STS for feminised seed, fertile pollen confirmed: *Established* [2].
- Hermaphrodite and reversed-female pollen gives female progeny: *Established* [2][4].
- Spray timing details: *Grower practice*.
- Herm-prone feminised seed comes mainly from careless feminising (unproven donors, stress-herm pollen, no grow-out): GenetixBay house position (breeder experience). Well-selected, controlled-reversal feminised lines need not herm more than regular seed; controlled cannabis comparisons are limited.

## Sources

1. Lubell JD, Brand MH. 2018. Foliar sprays of silver thiosulfate produce male flowers on female hemp plants. HortTechnology 28(6):743-747. https://doi.org/10.21273/HORTTECH04188-18
2. Flajšman M, Slapnik M, Murovec J. 2021. Production of feminized seeds of high CBD Cannabis sativa L. by manipulation of sex expression and its application to breeding. Frontiers in Plant Science 12:718092. https://doi.org/10.3389/fpls.2021.718092
3. Ram HYM, Sett R. 1982. Induction of fertile male flowers in genetically female Cannabis sativa plants by silver nitrate and silver thiosulphate anionic complex. Theoretical and Applied Genetics 62:369-375. https://doi.org/10.1007/BF00275107
4. Punja ZK, Holmes JE. 2020. Hermaphroditism in marijuana (Cannabis sativa L.) inflorescences: impact on floral morphology, seed formation, progeny sex ratios, and genetic variation. Frontiers in Plant Science 11:718. https://doi.org/10.3389/fpls.2020.00718
5. USDA ARS. Silver thiosulfate (STS) solution preparation sheet. https://www.ars.usda.gov/ARSUSERFILES/80600500/HDM_DATA/Silver%20thiosulfate_STS_solution.pdf
6. Toth JA, Stack GM, Cala AR, et al. 2020. Development and validation of genetic markers for sex and cannabinoid chemotype in Cannabis sativa L. GCB Bioenergy 12(3):213-222. https://doi.org/10.1111/gcbb.12667