Feminized Seed Creation: Reversing Female Cannabis Strains

The biological science of female reversal

Feminized seeds are the backbone of modern home cultivation, ensuring that every seed germinated produces a productive female plant. To create feminized seeds, a female cannabis plant must be induced to grow male pollen sacs. Because the reversed female plant only possesses female (XX) chromosomes, any pollen it produces carries exclusively female genetics. When this pollen fertilizes another female plant, the resulting seeds are 99.9% feminized.

This sex change is achieved by blocking ethylene, a natural plant hormone that controls female flower development. Silver ions are highly potent ethylene antagonists. When sprayed on a female plant, they inhibit the plant's ethylene receptors, overriding its gender expression and forcing it to produce fully functional male pollen sacs filled with XX pollen.

Choosing your agent: STS vs. Colloidal Silver

Colloidal silver (CS) and Silver Thiosulfate (STS) are the two primary agents used for reversal. Colloidal silver consists of microscopic silver particles suspended in distilled water (typically 30-40 PPM). While safe and easy to buy, CS must be sprayed daily on every node from late veg until male sacs open. Daily application is tedious, and missed days can lead to a failed or partial reversal.

Silver Thiosulfate (STS) is a chemical compound mixed from silver nitrate and sodium thiosulfate. STS is systemic, highly effective, and only needs to be sprayed once every 5 to 7 days. Because of its reliability and ability to trigger complete reversals even on stubborn strains, STS is the standard choice for professional breeders and serious home growers.

Step-by-step: Mixing STS stock solutions

STS must be prepared carefully using distilled water. It consists of two stock solutions (Part A and Part B) that are kept separate and stored in light-proof brown bottles in a refrigerator until mixing the final spray.

Part A (Silver Nitrate): Dissolve exactly 0.5 grams of silver nitrate in 500 milliliters of distilled water. Stir with a plastic utensil until completely dissolved. Store in an amber bottle.

Part B (Sodium Thiosulfate): Dissolve exactly 2.5 grams of sodium thiosulfate anhydrous (or 3.9g of sodium thiosulfate pentahydrate) in 500 milliliters of distilled water. Mix until fully dissolved and store in a separate amber bottle.

To mix the active working solution (1:9 ratio): Pour 800ml of distilled water into your spray bottle. Add 100ml of Part B and shake well. Then, add 100ml of Part A and shake. Always add Part A to Part B (already diluted in water) to prevent the silver from precipitating out of solution.

The reversal spraying schedule

Timing is critical for a successful reversal. The donor plant (the female plant you are reversing) must be sprayed before it begins flowering.

Apply the first spray 5 to 7 days before flipping the light cycle to 12/12. Thoroughly soak the entire plant, focusing on the nodes where future branches and flowers will form.

Flipping the lights: Transition the plant to a 12/12 light schedule.

Subsequent sprays: Spray the donor plant once every 7 days (usually 3 to 4 total applications). Stop spraying once the male pollen sacs are fully formed and begin to swell.

• Day -7: Spray 1 (vegetative stage, 1 week before flip)
• Day 0: Flip lights to 12/12
• Day 7: Spray 2 (early transition)
• Day 14: Spray 3 (pollen sacs beginning to form)
• Day 21: Spray 4 (final spray, sacs swelling)

Collecting and storing XX pollen

By week 3 or 4 of flowering, the reversed plant will look like a male, covered in green pollen sacs. When the sacs begin to crack and show yellow pollen, turn off all intake and circulation fans in the room to prevent accidental pollination.

Gently tap the branches over clean glass plates, mirrors, or aluminum foil to collect the falling yellow powder. Use a fine sieve to separate any plant matter from the pure pollen.

To store pollen for future crosses: Mix the dry pollen with dry, baked flour at a 1:3 ratio (flour to pollen) to absorb moisture. Place it in sterile vials with silica gel packs, seal them, and store in a freezer where it remains viable for up to a year.

Targeted pollination and seed harvest

To create the seeds, pollinate your target female plant when it is in weeks 2 to 4 of flowering (white pistils are long and fuzzy).

Use a small artist paint brush to apply the collected XX pollen directly to the white pistils of specific branches. For a full seed run, you can shake the reversed donor plant directly over the recipient females in a separate enclosure.

After pollination, spray the treated branches with plain water after 2 hours to deactivate any stray pollen, preventing it from spreading to other buds in your tent.

Allow the pollinated buds to mature for a full 5 to 6 weeks. The seeds are ready when the calyxes split open, exposing hard, dark brown seeds with dark tiger striping.