Sex Reversal of Female Cannabis Plants, or One of Their Branches
I've wanted to try this for a while, but needed to get some growing experience first. Now the time has come to actually do it. I started by reading several threads here. The first I came across used colloidal silver (CS). Later I found out about silver thiosulfate (STS). Reading through several threads I found that CS was prone to failure, although many have used it successfully. STS seems to be a sure-fire method, so I chose that. Here are some links to threads I've found helpful:
About Silver Thiosulfate (STS):
After deciding on STS, I did a fair bit of research, including how to make, use, and store it. This is what I've found:
Silver thiosulfate (STS) is commonly used to block the action of ethylene in plant cell cultures. Ethylene is a hormone that is present in the gaseous state. Ethylene increases during senescence (aging, flower development) and ripening, and has been shown to increase in plant cell cultures due to wounding or the presence of auxins. Silver nitrate may be used alone to block the action of ethylene but it is not transported as well as STS thus is seldom used alone.
STS is the most commonly used compound, for creating stable feminized cannabis pollen. While it is not the only method, it is arguably the most commonly used and is quite reliable. Female cannabis plants require ethylene production to form female flowers. STS suppresses ethylene production in the plants, so they will produce male flowers. As the genetics are totally female, the pollen used on female flowers will result in about 99.9% female seed.
Ethylene is a hormone produced by female plants and used to build pistilate flowers. Ionized silver inhibits ethylene production so the plant will produce staminate flowers instead. The are every bit as stable as there male counter parts. Being genetically female the pollen sacs can only produce pollen with female chromosomes. 99% of off spring will be female.
Most sources agree on the 1:5 ratio of silver nitrate to sodium thiosulfate. Some use a 1:4 ratio. Several sources state that metal implements should not be used while making STS. Some sources mention that the silver nitrate solution and STS will stain almost anything they come in contact with. I have verified this. Wear gloves and cover your work surface with wax paper. All sources agree that silver sitrate and sodium thiosulfate should be dissolved separately in distilled water. (Note: Use distilled water, or water from an RO with a de-ionizer. The TDS must be below 5 PPM. Never use tap water, as the silver nitrate and sodium thiosulfate will bond with compounds in the water rather than with each other.) Some sources use a more concentrated silver nitrate solution, but in the end the solution sprayed on the plants has identical silver content. Both the concentrated and diluted solutions should be clear. If they have turned brown, they should be discarded. Many sources recommend the addition of a surfacant to the diluted solution. Yucca extract is often used, although dish detergent is also an option.
There are a wide range of instructions for the use of STS. Some start application of STS three weeks before switching to 12/12 lighting; others start two weeks after the switch. This thread is the only one recommending a single application. Other sources recommend up to once every five days for five weeks.
The dry chemicals can be stored in a cool, dark place indefinitely, as can parts A and B before they are mixed together to form the concentrate. One source states that the concentrate can be stored in a cool, dark place for up to nine months, but will have degraded somewhat by that time. Other sources state it should be used within a month or two. Most sources agree that the solution diluted for application to the plants should be used within a week or two.
I'm about a week away from needing STS, so I've mixed up a batch...
Making STS:
Most sources dissolve 0.5gm silver nitrate and 2.5gm sodium thiosulfate in 500ml ml in separate containers. The silver nitrate solution is then mixed into the sodium thiosulfate solution while stirring rapidly to form a concentrate. The concentrate is then diluted with nine times its volume to make your working solution. This approach makes ten liters of the working solution, far more than most of us will use in our lifetimes. I strongly suspect that the reason for this approach is the tiny amount of silver nitrate used. A scale such as many of us have with 0.01 gm resolution that reads exactly 0.5 gm will have measured the silver nitrate with a 2% accuracy.
I have a scale with 0.001 gm resolution, so I chose to make a smaller amount of 200ml of the silver nitrate and sodium thiosulfate solutions. The amount of silver nitrate required drops to 0.2 gm, and the accuracy increases to 0.5%. I could drop to 100 ml or even 50 ml of the silver nitrate solution for a 1% or 2% accuracy, but those quantities are very difficult to measure out. For my purposes 0.2 gm ± 0.002 gm or a 1% accuracy is acceptable. The updated instructions are:
To make 200ml stock solutions:
For Part A, dissolve 0.2 gm silver nitrate into 200 ml distilled water;
For Part B, dissolve 1.0 gm sodium thiosulfate in 200 ml distilled water; and
Store Parts A & B in separate containers in a cool dark place until needed.
These solutions should last indefinitely. If your working solution turns amber or brown as you mix it, discard your stock solutions and make new ones.
Making Part A and Part B Stock Solutions
Note that the sodium thiosulfate crystals are quite large. I needed to break one up to get this close to the required amount. With the stock solutions on hand, it's time to make a working solution. I don't want a lot of it, just enough to reverse a branch or two on three plants. I decided that 200ml would be a reasonable amount.
To make 200ml of STS working solution:
Slowly mix 10 ml of Part A into 10 ml of while stirring rapidly;
add 180 ml distilled water while continuing to stir the solution; and
pour the working solution into an amber bottle.
The working solution should be discarded when it starts to turn amber or brown.
Note: I sourced the dry chemicals through e-Bay. The silver nitrate came from Riga, Latvia, and the sodium thiosulfate came from Guangzhou, China.
I intend to try spraying some branches, and painting the solution on others to determine the best way of applying the STS working solution. This will be covered in a future post.
Looking forward to see how it works for you
