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 action and leads the plant to form male flowers with fertile pollen (Ram and Sett 1982; Lubell and Brand 2018). It is the standard agent for making feminised and S1 seed.
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 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.
