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Silver Thiosulfate Solution (STS) Spray 16 oz


Availability: 4 in stock (can be backordered)

Phoenix Farms’ Silver Thiosulfate Solution (STS) spray 16 fl oz. is specifically formulated to create feminized seeds for home and commercial growers. STS is more effective than colloidal silver at producing feminized seeds but is also more difficult to use. Some studies have shown that colloidal silver can reduce seed germination rates and yields. STS is a chemical compound, so it is important to follow the instructions carefully to avoid damaging the plants. It is also crucial to reverse females in a space you know will not trigger hermaphrodite tendencies. The feminization rate is approximately 95% for all types of plants.* 

Here is a table that summarizes the key differences between STS spray and colloidal silver spray:

Characteristic STS spray Colloidal silver spray
How it works Inhibits the production of ethylene Disrupts the cell membranes of male pollen sacs
Effectiveness More effective Less effective
Difficulty of use More difficult Less difficult
Safety More care needed to avoid damaging plants Less likely to damage plants


This product is premixed and ready to use; do not dilute unless you see signs of burning (see below)

Wear gloves, safety glasses, and a face mask. Turn off all fans and lights. 

To keep STS out of your soil, try to use newspaper or a plastic barrier until dripping stops from application.

After your lights are turned off for the night, apply STS Spray liberally to a female plant starting four days after starting your bloom or “flowering” stage the lights; repeat every three to five days for two to three weeks or until pollen sacs appear and are well developed. 

Depending on your needs, spray a whole plant or just one branch. 

Dilute Solution if your plants show signs of burning. Some strains/phenotypes of cannabis are more sensitive than others. A slight reaction is acceptable, while severe reactions require diluting with additional distilled or r/o water. Simply open the spray bottle and top it off with distilled or R/O water.

Continue spraying and growing until pollen sacs open and produce pollen. Collect the pollen by gently shaking the male flowers over a container. The pollen will fall into the container and can then be stored. Pollen should be dried first and stored in a cool, dark place. To dry pollen, spread it on a piece of paper or cloth in a well-ventilated area. The pollen should be dry within a few days. 

Apply pollen with a Q-tip or tiny paint brush to female “buds” or flower sites. We recommend starting your proposed male plants two weeks before planting your female candidates to ensure your females aren’t blooming before your males. 

Let developing seeds fully mature or ripen by extending your flowering time by two weeks past the regular harvesting date. 

It is worth noting that reversing a female with STS will produce stable feminized pollen. At least as stable as the parents are. Reversing a female known to hermie with light leaks in a room or other stressors will create both feminized and hermaphrodite pollen. I.e. you will get female and hermie seeds. The same is true for any plant with hermaphroditic tendencies that is flowered in a space with those triggers. You won’t be able to tell which flowers produce hermie pollen and which produce valuable feminized pollen since the flowers look the same. Therefore, it is crucial to reverse females with the right genetics and in a space you know will not trigger hermaphrodite tendencies.


Silver Thiosulfate Solution is light and temperature-sensitive. Store in your refrigerator or a cool, dark place. 


Ninety days from the purchase date. 


Phoenix Farms is a veteran-owned and operated small business. 

*Please note that there is no chemical formula that will feminize all phenotypes of plants 100% of the time. You should experiment and learn what works for your specific plant strain. 



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