Ethylene in Cannabis – the Hormone Behind Sex, Stress and Feminized Seeds
When a cannabis plant changes its visible flower type, one single molecule is almost always at the end of the chain: Ethylene. It is the central hormonal switch of sex determination – and at the same time the plant’s classic wound hormone. That explains why stress so often pushes toward female and how feminized seeds come about.
What ethylene is
Ethylene is a gaseous phytohormone. Plants produce it during ripening, ageing and above all as a stress response. The biosynthesis runs from the amino acid methionine via S-adenosylmethionine (SAM) to 1-aminocyclopropane-1-carboxylic acid (ACC) and from there to finished ethylene. The rate-limiting step is ACC synthase – it determines how much ethylene forms.
Ethylene steers the sex
The visible sex expression hinges on a balance of phytohormones. Ethylene, auxins and cytokinins promote female flowers, gibberellins male ones. Ethylene is the strongest feminizing cue. Because the chromosomal sex does not finally fix the visible flower type – hence sexual plasticity – this hormonal switch can even flip the expression completely, up to full sex reversal.
The wound hormone – why stress pushes toward female
Ethylene is not only produced on schedule but also on wounding: a mechanical injury upregulates ACC synthase within minutes and triggers an ethylene burst. This closes the loop with hermaphroditism and stress-induced switching: a hard cut-back or broken branches create an ethylene cue, and that cue steers expression toward female. Both single steps – wounding produces ethylene, ethylene feminizes – are well documented; the combined pathway specifically in cannabis is mechanistically plausible but has not been measured directly in a dedicated cut-back experiment.
STS and Ethephon – the switch in both directions
Seed production exploits the controllability of this switch, in both directions:
- Silver thiosulfate (STS) blocks the action of ethylene. Without this signal, a genetically female plant forms male flowers – the basis of seed feminization.
- Ethephon, conversely, releases ethylene and makes genetically male plants form female flowers; in controlled trials over 80 % of flowers were converted.
This is described here as a working principle, not as an application guide.
An honest classification
The hormonally forced reversal comes from the lab, with targeted agent application. A spontaneous garden effect from stress alone follows the same mechanism but is less predictable and more poorly documented. Ethylene explains the how, not the guarantee of a particular outcome.