Silver Thiosulfate (STS)

STS Chemical Structure

Silver Thiosulfate (STS) is made into a solution and then sprayed onto female cannabis plants frequently during flower to help reverse the sex of the plant so that it instead produces feminized seeds.

Only half a gallon is needed at a time for each treatment for about 4 plants. You can purchase the solution online or easily make it yourself with a few key ingredients.

How to Make your own STS Solution

sts solutionIngredients:

  • 1 Gallon of Distilled Water
  • 0.5/Gram Silver Nitrate Powder
  • 2.5/Grams Sodium Thiosulfate Powder
  • 2 500/ML Glass Containers
  • 1 1000/ML Glass Container


  1. Use 0.5 grams of silver nitrate in 500/ML of Distilled Water (Stir until fully dissolved)
  2. Use 2.5 grams of sodium thiosulfate in 500/ML of Distilled Water ( Stir until fully dissolved)
  3. Pour (simultaneously) both 500/ML mixtures into empty 1000/ML Glass Container
  4. You now have a 100% STS Solution or 1:1 ratio, still need to dilute it to a 1:9 ratio
  5. Combine 100/ML of STS 1:1 Solution with 900/ML of Distilled Water in a spray bottle
  6. You now have a 10% base STS Solution to start spraying your plants with

When to Spray

  • Start spraying 1 week before putting the plants into flower
  • Spray the entire plant until you see tiny run off including the leaves, stem, and stalk
  • Spray again the 1st day of flower, then every 3 days for 7-9 total times (10-11 for stubborn plants)
  • Spray until day 22ish –  the cannabis plant should start to show signs of reversal

Other Notes

Sometimes leaves a purple stain behind, so use with caution and spray in a certain tent, room, or outside area.


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