Feminized seeds are a valuable resource for cultivators seeking to grow plants that will develop exclusively into female individuals. This eliminates the need to identify and remove male plants, which do not produce the desired flowers and can inadvertently pollinate the female crop. The process hinges on inducing a female plant to temporarily develop male reproductive organs, a technique most effectively achieved using a chemical compound called Silver Thiosulfate (STS). STS is the preferred method for this sex reversal because the resulting pollen carries only female genetics, ensuring that any seeds created are feminized. This specialized breeding technique is utilized to preserve desirable traits from a single mother plant and increase the overall efficiency and yield of a grow operation.
The Chemical Mechanism of STS
Silver Thiosulfate functions as an inhibitor of the plant hormone ethylene, which is naturally responsible for promoting female flower development. Ethylene is a gaseous hormone that acts by binding to specific receptors within the plant’s cells. When STS is introduced, the silver ions effectively block these receptors, preventing ethylene from signaling the plant to continue its female growth pattern.
This interruption essentially tricks the genetically female plant into stress-induced masculinization. The plant shifts its hormonal balance, forcing the development of male reproductive structures, specifically pollen sacs. The pollen produced by these induced male flowers is unique because it contains only X-chromosomes, the sex chromosomes found in female plants. This X-chromosome-only pollen guarantees the resulting seeds will be female when used to pollinate an untreated female plant.
Mixing the Silver Thiosulfate Solution
Creating the Silver Thiosulfate solution requires combining two separate components: Silver Nitrate (AgNO₃) and Sodium Thiosulfate (Na₂S₂O₃). Both chemicals must first be dissolved into separate solutions, Solution A (Silver Nitrate) and Solution B (Sodium Thiosulfate). It is necessary to use distilled or reverse osmosis (RO) water for all mixing steps, as tap water impurities can cause precipitates that reduce the solution’s effectiveness.
A common and effective concentration is achieved by preparing a 0.1 M stock solution of each component. For instance, a 0.1 M Silver Nitrate solution is made by dissolving 1.7 grams in 100 ml of water, and a 0.1 M Sodium Thiosulfate solution uses 1.58 grams in 100 ml of water. The final STS solution is created by slowly pouring the Silver Nitrate (Solution A) into the Sodium Thiosulfate (Solution B) while stirring rapidly. This specific mixing order is important to ensure the silver is properly chelated by the thiosulfate, forming the active complex that inhibits ethylene.
The final mixture should maintain a molar ratio of 1 part silver to 4 parts thiosulfate to form the active complex. A standard working solution for application is often around 20 mM, achieved by mixing the stock solutions in a 1:4 ratio. The mixed STS solution should be stored in a cool, dark environment, such as a refrigerator, and is most effective when used within 30 days.
Application Timing and Pollen Collection
The application of the STS solution must be timed precisely to maximize the induction of male flowers on the female plant designated for reversal. The optimal time to begin spraying is just before or at the very beginning of the flowering cycle, typically a few days before switching the light cycle to 12 hours of darkness. Some protocols suggest a single, heavy application, while others recommend a series of sprays to ensure complete coverage and sustained ethylene inhibition.
When spraying, the solution should be applied thoroughly to the entire plant until slight runoff occurs, ensuring all potential flower development sites are saturated. It is best to apply the spray when the lights are off or just before the dark cycle begins, as STS is sensitive to light and this practice also helps prevent leaf burn. The application is typically repeated every three to seven days for a period of two to three weeks, or until the first male pollen sacs begin to form.
After approximately four to six weeks from the initial application, the treated female plant will develop clusters of male pollen sacs in place of female pistils. Pollen collection begins once these sacs swell and appear ready to open but before they naturally burst and release their contents. The sacs or small branches bearing them should be carefully removed, dried in a clean, dry, and cool environment, and then gently agitated to release the fine, yellow pollen. This collected pollen must be kept dry and can be stored temporarily in airtight containers in a cool, dark place until it is ready for use in the final pollination step.
Producing and Curing the Feminized Seeds
The final stage involves using the collected feminized pollen to fertilize a separate, untreated female plant, often referred to as the “mother” or “seed-receiving” plant. To control the pollination and maximize seed production, it is common to apply the pollen only to specific branches or flower sites, isolating them from the rest of the plant. The pollen can be applied directly using a small brush or a cotton swab, dusting the white pistils of the receptive female flowers.
Following successful pollination, the female plant requires a waiting period for the seeds to mature, which typically takes between four to six weeks, depending on the specific strain. During this time, the ovules swell and begin to harden as the seed develops inside. Mature seeds are identified by their hard shell and dark color, often displaying a distinctive tiger-stripe pattern. Immature seeds are generally small, soft, and pale white or green and should be discarded.
The seed-bearing branches are harvested once the seeds are visibly mature, and they should be dried slowly in a controlled, well-ventilated environment. After drying, the seeds are carefully extracted from the dried flower material and separated from any debris. The final step is curing the seeds, which involves ensuring they are completely dry before long-term storage in a cool, dark, and airtight container to maintain viability.