Tutorials [Sticky] How to make Silver Thiosulfate (STS) for creating feminized seeds

As we progress through growing it seems to be a natural desire to learn to make feminized cannabis seeds. The best way I’ve found to do this is with STS spray. When you spray a normal female cannabis plant with STS, it causes the female plant to produce pollen instead of female flowers. This pollen can be used to make all female seeds. 

Making homemade STS solution for reversing female plants

What you will need

1. Silver nitrate, it’s relatively expensive but you won’t need much
2. Sodium Thiosulfate (anhydrous or pentahydrate, amounts will be different)
3. Distilled or RO water
4. 2 dark colored stock bottles with tight fitting caps, 500ml or more
5. One 240ml spray bottle, dark colored glass works great
6. a container to mix chemicals in, a liter or more in volume
7. Scale, must be able to measure down to 1 milligram
8. Rubber gloves, mask, and safety glasses (safety equipment)

I’m not going to cover how to use the safety equipment, just put it on now before we start. You only get one set of eyes and lungs so take care of them!

Start by measuring 2 grams of Sodium Thiosulfate Anhydrous or 3 grams of Sodium Thiosulfate Pentahydrate, depending on which one you have. You don’t need or want both, either one will work just fine. The pentahydrate has some extra water molecules so it takes more to do the job. I use the Sodium Thiosulfate Anhydrous in my STS. Put the measured chemical in a container and add 500ml of distilled or RO water. Mix until all powder is dissolved then pour into a dark container. Label this solution “A” and put aside

Thoroughly clean your mixing container or use a clean one in the next step

Measure 0.4 grams of silver nitrate and put it into your mixing container. Add 500ml of distilled or RO water and stir till the powder is dissolved. Move the mixture to a dark glass container for storage and mark this “B”. Set aside.

These 500ml stock bottles can now be used to create ten, 500ml bottles of STS spray. Store these stock bottles in a dark refrigerator and they should be good for at least one year. When you’re ready to use the STS spray, divide the total volume of the spray you want to make by 10. As an example, I use a 240 ml bottle so dividing by 10 is 24ml. I add 24ml of “B” solution to the empty bottle, then add 24ml of “A” solution. It’s very important that you always add “B” first or the reaction will suffer. After the 2 solutions are gently mixed, fill the bottle with distilled water and then add several drops of dish soap for a surfactant. Spray the nodes of the plants to be reversed every 5 days with this mixture for 6 applications and you should see the male flowers form. Mixed STS is good for about one month if stored in a dark container and in the refrigerator.

In my opinion this was tons easier than making Colloidal Silver, worked easier and was consistently more reliably. This all comes from a YouTube video.

There’s a video there that shows how to make STS in single size bottles at a time. I didn’t try it so I didn’t link it. It might work but I know that this absolutely works for me.