STS Reversal Spray


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STS Reversal Spray

After much experimentation and recipe adjustments we have finally developed a winning formula for our STS reversal spray. This seed reversal spray has been specially formulated for cannabis by the team at Twenty20 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 in mind that different strains react differently to STS reversal spray.

STS Reversal Spray Feminized Cannabis Seeds


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

For commercial seed production you will want a ratio of approximately 1:4 donor plant to receiver plants. in other words if you have 12 plants to start with you will want to reverse 3 of them.

*Although it’s possible to reverse a single branch and try to pollinate other branches from the same plant, it’s not the recommended method since the timing of pollination compared to the formation of the plant’s reproductive structures may not be ideal.


  • -You must start the flowering and STS reversal spray regimen on the chosen reversal plants between 14 – 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. .
  • -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. For photoperiod cultivars, start the spraying process on the first day of flowering for your “donor” plant. For autoflower cultivars, spray as soon as the first signs of reproductive growth are visible. Spray the plant every other day for a total of 4 sprays. It’s very important not to expose the plants to STS after the flowers start to form. Be patient, sometimes it’s difficult to see the pollen sacs forming in the flower. Typically it will be quite obvious between day 17-24. Be prepared to start flowering your “receiver” plants about 14-18 days after you started the reversal process. (See footnote 1)
  • -Wait to pollinate female plants until the flowers are about the size of a thumbnail, usually about 15-20 days.
  • **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.
  • -Healthy plants = healthy, abundant pollen. Don’t neglect your reversals and treat them like second class citizens. It’s important to provide them with the best conditions possible.
  • -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.

Caption 1. Reverse Female Plant Exhibiting Signs of Male Flowers Exactly 15 days After beginning STS reversal spray regimen.

Caption 2. A reversal plant at day 21. Keep in mind, progress of flowers can vary greatly from cultivar to cultivar.