How to Use STS Spray (Silver Thiosulfate Instructions)
Silver Thiosulfate (STS) is a chemical compound used by specimen physiologists and horticultural breeders to block ethylene action. Ethylene is the specimen hormone responsible for female sex expression. By applying STS, you temporarily block ethylene production, forcing a female specimen to produce male pollen sacs containing only female (XX) chromosomes. This pollen can then be used to pollinate another female, resulting in 99.9% all-female offspring.
Required Safety Gear (PPE)
STS is a chemical reagent. Always handle with care using proper protective equipment. You can purchase these directly from our shop:
Protects hands from chemical skin irritation and temporary brown/black staining.
Prevents inhalation of fine mist during spraying.
Protects clothing and skin from silver staining.
Prevents eye contact with the chemical mist.
Preparation & Dilution
If you are using the Breeder Dry Kit, mix the dry chemical packets with distilled water according to the instructions on the package to prepare 10 Liters of stock solution. If using our Ready to Spray bottle, shake well before use.
Precise Timing & Flower Initiation
Timing is critical to successful specimen reversals. For photoperiod flora, start applying STS spray 12 days before flipping the lights to 12/12. For autoflowering or non-photoperiod cultivar apply on day 17 or when the first white pistils appear, whichever comes first.
Foliar Application Protocol
Spray the target specimen thoroughly, focusing on nodes and growth sites. Avoid spraying the root zone. Ensure minimal air movement during application until the leaves absorb the solution completely.
Post-Treatment Dark Period
Immediately after spraying, place the flora in complete darkness for 6 hours. This enables the silver thiosulfate to block ethylene receptors without being degraded by light. Once dry, normal ventilation and fans can be turned back on.
Pollen Collection & Storage
Pollen sacs will begin to develop in place of female flowers. Once mature, gently tap or shake the sacs over clean glass or parchment paper. Collect the fine powder, dry it at room temperature with 30-40% relative humidity, and store in a cool, dark, airtight container.
STS Spray Schedule
First Foliar Application
Spray the selected branch or the entire donor plant thoroughly. Apply during the light-off transition or in complete darkness. Ensure the leaves are wet but not dripping into the root system.
Second Foliar Application
Perform a second complete spray. This build-up of silver ions blocks the early flower cycle hormone receptors, preventing pistils from forming.
Third Foliar Application & 12/12 Trigger
Flipping the photoperiod timer. Perform the third application immediately. For autoflowering strains, this corresponds to the day first pre-flowers are observed at the nodes.
Foliar Top-up (Optional)
Perform a final spot spray on stubborn growth nodes. Observe the nodes; they should start swelling without forming white hair-like pistils.
Sacs Development
Discontinue all STS sprays. Male pollen sacs will now develop rapidly in place of female flowers. Maintain normal canopy airflow and moderate humidity.
Pollen Harvesting
Pollen sacs will crack open. Gently shake the branches over parchment paper. Store the pollen immediately in air-tight micro-tubes at 0°F with desiccant beads.
Frequently Asked Questions
Absolutely not. Any plant material sprayed with Silver Thiosulfate must be discarded and never consumed, combusted, or extracted. Silver compounds accumulate inside the cellular walls of treated plant tissues and are toxic if ingested or inhaled.
Once mixed, STS solution remains potent for 3 months when stored in a dark container inside the refrigerator. It can also be frozen for up to 9 months. Store the STS solution in the refrigerator at all times when not actively in use to prevent chemical degradation. Unmixed dry kits have a shelf life of over 2 years.
Some reversed plant varieties produce sterile pollen or sacs that do not open naturally due to genetic factors or high room humidity. If sacs fail to open, harvest the mature sacs manually, allow them to dry out on parchment paper for 24 hours, and then crush them lightly to release the pollen grains.
Yes. However, because autoflowers have a preset vegetative cycle that cannot be delayed, timing is critical. You must apply STS early—usually on Day 17-21, or at the first sign of sex pre-flowers. A late application will result in partial reversals where female flowers continue to form alongside sterile sacs.
For most stable cultivars, a schedule of three sprays (Day -12, Day -5, and Day 1) is sufficient. Stubborn or hard-to-reverse genetics may require a fourth application 7-10 days into flower. Discontinue all sprays once male pollen clusters begin to swell.
The Breeder Dry Kit contains dry chemical packets that must be mixed with distilled water, making 10 Liters of solution (best value for shipping). The Ready to Spray is pre-mixed and diluted to the exact horticultural concentration, ideal for immediate application in small-scale projects.
Store collected pollen in small microcentrifuge tubes or vials, mixed with a tiny amount of dry baking flour (baked at 300°F to remove moisture) or silica gel desiccant packs. Store in the freezer for up to 1-2 years. Avoid constant temperature fluctuations.
