How to Make Feminized Seeds with Silver Thiosulfate (STS)

So, you’ve got a prized female cannabis or hemp plant — the kind you wish you could clone forever. But what if you could take that queen and make her produce seeds — without ever introducing a male?

That’s where Silver Thiosulfate (STS) comes in.

Used by breeders around the world, STS is the go-to method for creating feminized seeds, meaning the offspring are 99.9% female. No guesswork. No dude plants. Just reliable, consistent genetics ready to grow.

Here’s how it works — and how you can do it yourself at home.

🧪 What Is Silver Thiosulfate (STS)?

Silver Thiosulfate is a solution made by combining Silver Nitrate and Sodium Thiosulfate. When applied to a female cannabis plant, it blocks ethylene production, the hormone responsible for female flower development.

With ethylene suppressed, the female plant reverses and produces male pollen sacs — but because its DNA is still female, the resulting pollen only carries X chromosomes.

✅ When this pollen is used to fertilize another female (or the same clone), the seeds produced will also be female.

You can grab a ready-to-mix version of STS right here if you’re ready to start your own feminization journey.

🌿 Step-by-Step: How to Use STS to Make Feminized Seeds

🧴 What You’ll Need:

STS kit (or mix from Silver Nitrate + Sodium Thiosulfate)
Spray bottle (dark glass preferred)
Gloves, mask, and goggles
A healthy female plant or clone (must be at least 2 weeks into veg)

🧪 Mixing STS Solution

Most STS kits include two parts:

Solution A: Silver Nitrate + water
Solution B: Sodium Thiosulfate + water

Mix Solution A and B in equal parts right before use (do not store after mixing).
Final STS mix should be 10:1 water to STS, unless otherwise directed by your supplier.

👉 This version makes the process easier and safer with pre-measured components.

🚿 Application Process

Choose a branch on the plant that will not be smoked — this is your reversal site.
Start spraying 5–7 days before switching to 12/12 light cycle.
Spray daily or every other day for 10–14 days, focusing on new growth.
Keep the plant away from others to prevent pollen contamination.
Within 2–3 weeks of flowering, you should see male pollen sacs forming on the reversed branch.

🌼 Pollination + Seed Collection

Once pollen sacs mature (they’ll swell and split), you can:

Collect the pollen gently with a paintbrush or spoon
Apply to another female plant’s buds in early flower (~day 14 of 12/12)
Wait 4–6 weeks for seeds to mature
Harvest, dry, and collect your feminized seeds

💡 Tip: If reversing a clone, you can safely pollinate its twin — this is the classic S1 feminization technique.

⚠️ Safety Notes

STS is toxic and should only be used with gloves, goggles, and a mask
Never spray near plants intended for consumption
Dispose of unused solution properly — do not pour down the drain

🎯 Why STS Beats Other Feminization Methods

Method	Stability	Feminization Rate	Ease of Use	Risk
STS (Silver Thiosulfate)	✅ High	✅ 99.9%+	Moderate	Low*
Colloidal Silver	Medium	95–98%	Easy	Low
Rodelization (Stress)	Low	50–70%	Easy	High (intersex risk)

STS is widely considered the most reliable and stable feminization method in both cannabis and hemp breeding.

🧬 Final Thoughts: Feminized Seeds, Made Right

Making your own feminized seeds isn’t just possible — it’s powerful. With a little science, some care, and the right gear (like this STS kit), you can preserve, expand, and replicate your favorite genetics on your own terms.

Just remember:

✅ Always reverse stable females
✅ Use protection (PPE and distance!)
✅ Don’t smoke the reversed plant
✅ Label everything!