STS Spray


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2-Part Mixture of our house formula Silver Thiosulfate (STS) Spray to be used for sex reversal of female plants. Unlike pre-mixed STS, this 2-part mixture is indefinitely shelf stable until mixed. Pre-mixed STS oxidizes quickly and loses efficacy after approximately 30 days. This kit contains everything you need to make 250ml of solution, enough to reverse 1-2 plants (18″-24″ tall). Just add DISTILLED water.

After much experimentation and recipe adjustments we have finally developed a winning formula for STS plant reversal spray.  This spray has been specially formulated for cannabis by the team at Twenty20 Mendocino and is the exact recipe we use to make feminized seeds.

It is important to note that reversing the sex of a female cannabis plant is simple.  The difficult aspect is timing the reversal properly and collecting an adequate amount of pollen for the pollination process.  We will outline the procedure we follow in order to provide you with as much information as possible to successfully create your own feminized seeds.  Please keep on mind that different strains react differently to the spray.


Separate the plants you plan to reverse from the plants you plan to pollinate.  The reversal plants will perform best if they are multi-topped plants as apposed to single top plants.  It is best to prepare ahead and pinch the tops to facilitate this process.

For abundant seed production you will want a ratio of approximately 1:4 reversed plant to seed mothers.  In other words if you have 12 plants to start with you will want to reverse 3 of them.  This ratio only applies to commercial seed producers.   (see footnote 1)


-You must start the flowering and spray regimen on the chosen reversal plants approximately 21 days before you flower the seed mothers.  This timing ensures you get maximum pollen production around the time the female plant is in her reproductive prime.  21 days represents the approximate average used by the team at Twenty20.  This can vary between 14 days and 25 days. 

-The spraying process begins the day before you switch the reversal plant(s) to flower.  This should be done soon after the lights go off or soon after dusk for outdoor plants.  Spray the nodal areas, and branches and tops.  It is not necessary to spray the entire plant and all of the leaves.  A fine mist will do but be sure to get an adequate coating.  This process should be completed every 3rd day until the first male pollen sacs begin to open.  This is usually around day 20-30.  (see Caption 2.)

-At day between day 14 and day 25, start the flowering process on the female seed mother plants.  (See footnotes 1)

-After the female plants have a small cluster of stigmas they can be united with the reversed female plants for pollination.  We usually do this when the stigmas are protruding but before the calyxes begin to swell.

 **Reversed female plants do not produce as much pollen as male plants so it is important to take a few steps to insure proper pollination.  

 -Always provide adequate airflow to the cultivation area with fans.

-Agitate the reversed plants daily by shaking them gently in front of fans

-Keep the humidity as low as possible; this will increase the amount of airborne pollen.  This also helps minimize mold, which can be more prevalent in reversed female flowers. 

-If particular reversed plants tend to produce more pollen be sure to shift them around the cultivation area

-You should see signs of successful pollination within a few days of joining the plants.   Be patient, the process is much slower and less effective than breeding with males. 


For further instructions please watch this video.