sts spray for feminized seeds

How to use STS to feminize seeds

What you need:

Feminized seeds – each of you has certainly heard of them, and maybe you have even used them yourself.
Of course, I am talking about feminized seeds, with which there is no problem regarding sex, nor their selection. As you know, prices of seeds are dropping everywhere, but despite the widespread crisis in recent years, the purchase of seeds is still associated with the need to spend several dozens of Euros for a package of 10 seeds and often receive poor quality varieties for the money you pay. Necessity is the mother of invention, so some of you have probably wondered about the production methods used by professional seed makers.

The techniques they use are strictly confidential and we cannot count on getting a detailed description of the production technique they use individually. Hiding behind trade secrets, they only smile encouraging you to buy their products. In today’s article, I will describe one of the possible ways to obtain feminized seeds at home using silver ions derived from silver nitrate decomposed in the presence of anhydrous sodium thiosulfate. It’s not the best method, it’s not the only one, but it’s proven and it works. With a bit of self-denial, work and luck, which nothing can do without, you will be able to make your own homemade feminized seeds. I invite you to read on …

Preparation of the STS preparation:
It is formed when solutions of Silver Nitrate and Sodium Thiosulfate are mixed. Such a ready-made mixture is not suitable for long-term storage and it is best to make it just before spraying.
Silver Nitrate and Sodium Thiosulfate alone can be stored without any problems. Ideally, this place should be dark and cool (a refrigerator is perfect).

IMPORTANT: mixing solutions as well as individual components is done with plastic or glass objects. WE DO NOT USE METAL OBJECTS !!!

We need a few items:

  • 2 plastic containers, cups in which we will mix each of the solutions 
  • 2 plastic syringes (different syringe for each solution) 
  • 2 plastic spoons or glass sticks (to mix each solution with a different one) 
  • 1 pair of latex or similar gloves (so as not to get your pretty hands dirty) 
  • 2 sealed glass or plastic containers, bottles, etc. (to keep solutions separate) 
  • 1 glass or plastic sprayer (for the ready-made STS preparation to spray the plants) 

We need to make two solutions and we will call them “A” and “B”…
Solution “A” is made of Silver Nitrate (AgNO3) by mixing it with distilled water in the following proportions:
1.4 grams per 80ml distilled water (producing ready solution “A”)

We make solution “B” from Sodium Thiosulfate (Na2S2O3) by mixing it with distilled or plain water in the following proportions:
5.2 grams per 320 ml of distilled or plain water (obtaining a ready solution “B”)

This resulted in two solutions of 80ml (“A”) and 320ml (“B”)…

Now I will give you a recipe for making the base of the STS solution, which I liked the most and which has already proven itself several times. So, to get the base solution, we take, for example, 20ml of solution “A” and 80ml of solution “B”.

Without delving into molar units, etc… because what do we need it for?

REMEMBER add the Silver Nitrate solution (A) to the Sodium Thiosulfate solution (B) while stirring slowly!!!

After mixing the “A” and “B” solutions in these proportions, we get 100 ml of the finished product, which is intended to be mixed with distilled water to perform the treatment on plants.
My proportions are 1 part of the stock solution, i.e. 100ml and 3 parts of distilled water, i.e. 300ml.
Together we should get 400ml of plant spray.

We spray this preparation only ONCE!

Of course, you can set the proportions yourself and you don’t need to make large quantities, unless you are mass-producing seeds.

Proportions that can also be used, for example:
1:1 – So 1 part stock solution (Mixed together “A” + “B”) and 1 part distilled water
1:2 – So 1 part stock solution (Mixed together “A” + “B”) and 2 parts distilled water
1:3 – given above
1:4 – So 1 part stock solution (Mixed together “A” + “B”) and 4 parts distilled water

You can also mention weaker concentrations, with which we spray 3-4 times, every few days (4-8), and an example are:

1:7 – So 1 part stock solution (Mixed together “A”+”B”) and 7 parts distilled water
1:8 – So 1 part stock solution (Mixed together “A”+”B”) and 8 parts distilled water 1:9 – So 1 part stock solution (Mixed together “A”+”B”) and 9 parts distilled water

The STS solution is very efficient and you do not need to make large amounts of this preparation.
It is very simple and quick to prepare, so it can always be made just before feminization.

Plants before spraying
With normal varieties (i.e. not autoflowering) I spray as soon as the so-called “preflower” (first signs of sex) appear. Unless you have used feminized seeds and not regular seeds, spraying can be done earlier. But I usually wait for sex signs anyway. You do not need to spray the whole plants, you can do a local spray on the selected regrowth or several branches. However, it must be remembered that STS is quite efficient and can cover and spread on our bushes nicely. That’s why I spray the whole plant, and thanks to that there is no shortage of pollen and there is always something left for the next projects. Spraying, of course, is done outside the cultivation room to make sure that we did not accidentally treat a different plant than intended. You can prepare a larger cardboard box or old newspapers in advance, so as not to smudge everything around with the preparation. For this, I use a sprayer every time (to clean windows or to spray fertilizers).

After the treatment, I leave the plants alone until they dry out, and then I move them back to the growing room. Now all you have to do is wait patiently and don’t panic, because there are varieties that react differently to STS. Some cultivars start to show signs of transformation quite quickly, while others take longer. Therefore, patience is a virtue in this case.
More or less after 7 to 20 days, changes can be seen and male features appear, i.e. the so-called bananas, eggs (as you prefer to call them). I will add that each time the pollen was fertile and the male flowers opened by themselves. That’s probably enough for spraying normal varieties …

With Autoflowering varieties, the situation is identical, only we spray earlier on the plants that are to change sex. A good method that I use is simply to sow the seeds of plants intended for feminization in the further process. I try to keep this period at 14-20 days. After this time, I sow the next seeds, which will grow into the female generation ready for pollination. Thanks to this method, we have a nice synchronization of female plants and those that have been transformed. At the end, we are gifted with a large amount of our own seeds, of which we can be proud of. By applying yourself to feminization, you can get really good quality of different varieties, and sometimes even better than bought and overpaid.

Now a little more theory that we are turning into practice…
The process of feminizing cannabis seeds is a very complex biochemical process and its detailed explanation is beyond the scope of this publication! Beautifully set male flowers will produce pure female pollen and lots of great seeds.
The condition for obtaining satisfactory results is to have a so-called “genetically pure female”, because only she, after using the STS preparation, will start producing male flowers pollinating with pure feminized pollen. If, in this case, the “pure female” is automatically pollinated with her own female pollen, fertile seeds will be formed on the plant, from which only female plants will grow.

If you applied the STS preparation on a female specimen that is not, however, a “genetically pure female”, some of the seeds obtained will be hermaphroditic! They can produce a few male flowers on a female plant, or be the dominant form. Hermaphroditic individuals produce pollen and may consequently pollinate plants in their vicinity.

Clones grown several generations ago are best suited for feminization
In this case, there is a higher probability of finding a female with “pure genes”. In this case, we use the spray treatment with the STS preparation after about 3-4 weeks from the moment of switching the plants to flowering under the 12/12 lighting regime. After a few days from application, the plant will stop growing and turn yellow. This is a normal symptom of using STS. After a few weeks, the plants will return to a healthy green color and flowers of both sexes will begin to appear.

In the event that I am unable to grow from clones, batches of candidates for mothers of our feminized seeds should be subjected to strong stress. It will cause a dysregulation of the biochemistry of the plant and induce the production of natural hermaphrodites in plants with an admixture of male genes in them. Plants that are “genetically pure female” despite the stress applied to them will not show even the smallest male flowers.
And only these plants are suitable for the application of the STS preparation!

Small hermaphrodite flowers
Many physicochemical factors can be stressors for a plant, but the easiest to use and fully control is light. If you want to induce the formation of natural hermaphrodites, before selecting plants for feminization with the STS preparation, you should change the lighting regime every few days (5-7). After 7 days of 24 hour light on the plants, switch the clocks to 12/12 for the next 7 days. After 4-5 cycles of stress, the plants should be moved to the room where they will flower and must be watched very carefully to catch even the slightest signs of the appearance of natural hermaphrodites. They must be immediately eliminated from the garden and destroyed.

Pollen male flowers
After another 3-4 weeks under the final lighting, 12/12 if you haven’t found even the smallest male flowers, so-called bananas, you can proceed to the final feminization process by spraying your “genetically pure” female specimens with the previously prepared solution of STS working liquid. One liter of working liquid is usually sufficient for the correct application of 20-30 plants, depending on their age and size. After applying the STS preparation, the plants will slow down their growth and start to turn yellow. After 2 – 3 weeks the plants will begin to regain their healthy green color. Some of the largest leaves may wither and fall off, this is normal during feminization.

The pollinated female plants start producing seeds
The technique described above is one of many that result in female seeds. Every advanced farmer has his own secrets and “taste” of breeding. It is similar with the feminization of seeds with STS. Different farmers recommend slightly different doses and/or periods of application. As you acquire practice in plant feminization, you will certainly slightly modify the recipe given to you.


  • We mix, weigh products in a ventilated room, for all safety you should oxygenate rubber gloves, masks, glasses, silver nitrate is quite a toxic material, it should be handled very carefully, the residues should not be poured into the sink, so the best solution is to make such a amount of solution HOW WE WILL BE ABLE TO USE IT ONE TIME 

The total cost will not expensive.

Look on another article: Article on LAB – Lactic Acid Bacteria


  1. Ken Pacelli

    Why do you say to not mix with metal?

    1. Jakub Gajewski

      do not use metal parts for example spoons, etc.

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