Ethylene and STS: how fems are made in simple terms
Heard of feminized seeds (fems) that grow only girls? Ever wondered how they make them? It's all thanks to a gas called ethylene and a chemical compound known as STS (silver thiosulfate). Let's break down how this magic works in simple terms.
What is this ethylene thing?
Ethylene is a natural gas-hormone found in plants. It controls ripening, aging, and most importantly, determines the plant's sex.
How does plant sex depend on hormones?
Genetically, a plant's sex is set from the start: XX for a girl, XY for a boy.
But which flowers actually show up (buds or pollen sacs) is decided by the level of ethylene.
If ethylene is low or gets blocked, the plant will start growing male bananas (pollen sacs), even if genetically it's a 100% female.
How do they make fems (feminized seeds)?
Breeders use this exact ethylene-blocking trick:
They take a 100% female plant (XX).
They spray it with a silver compound — an STS solution. The silver completely blocks the plant from detecting ethylene, making the plant "think" it's a boy.
The girl starts growing pollen sacs, but genetically she is still female (XX).
They use this "female" pollen to dust another normal female plant. Since the pollen only carries X chromosomes (no male Y chromosomes exist here), the resulting seeds will be 99% female.
Why all the hassle?
Males are useless in a grow. They produce almost no THC, and if a male pollinates your girls, you end up with a box of seeds and dry hay instead of juicy sensimilla. Spotting and tossing males is a major headache and a waste of grow space. That's why fems are a must-have for any grower.
Science backing: A study by Timoteo Junior AA & Oswald IWH (2024) on optimizing feminized seed production in high-THC strains.
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