# STS

> STS (silver thiosulfate) is a silver compound sprayed on female cannabis to block ethylene action and induce fertile male flowers, the standard method for making feminised seed.

- Canonical: https://genetixbay.com/knowledge/glossary/sts.html
- Also written: silver thiosulfate, silver thiosulphate, silver thiosulfate solution, Ag-STS
- Glossary category: Genetics and breeding · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

STS is silver thiosulfate, a complex of silver ions with thiosulfate. Sprayed on a female cannabis plant before or at the start of flowering, it blocks [ethylene](https://genetixbay.com/knowledge/glossary/ethylene.md) action and leads the plant to form [male flowers](https://genetixbay.com/knowledge/glossary/staminate-flower.md) with fertile pollen (Ram and Sett 1982; Lubell and Brand 2018). It is the standard agent for making [feminised](https://genetixbay.com/knowledge/glossary/feminised-seed.md) and [S1 seed](https://genetixbay.com/knowledge/glossary/s1.md).

## In practice

Breeders treat one female or one branch, isolate it, and collect the pollen once the induced male flowers open, usually some weeks into flowering. The treated plant's flowers are not consumed. STS is more reliable than [colloidal silver](https://genetixbay.com/knowledge/glossary/sex-reversal.md) in published trials and in grower experience, because the thiosulfate complex moves through the plant better.

Silver compounds are hazardous to people and to aquatic life. Wear gloves and eye protection, keep treated material separate, and dispose of leftovers as chemical waste according to local rules. This glossary entry is a definition; preparation and dosing details belong in the main article.

## Don't confuse with

- **Colloidal silver**: a suspension of silver particles, used the same way but less consistent.
- **Silver nitrate**: an ingredient used to prepare STS; not the same compound.
- **Gibberellic acid (GA3)**: another hormone treatment that can induce male flowers, less used.

## Related terms

[Sex reversal](https://genetixbay.com/knowledge/glossary/sex-reversal.md), [Feminised seed](https://genetixbay.com/knowledge/glossary/feminised-seed.md), [S1](https://genetixbay.com/knowledge/glossary/s1.md), [Pollen](https://genetixbay.com/knowledge/glossary/pollen.md)

## Read more

- [Feminised seed and sex reversal: methods, with safety notes](https://genetixbay.com/knowledge/breeding/feminised-seed-sex-reversal.md)

## Sources

1. 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
2. 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
3. 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