Many growers know that if you stress out cannabis plants, they can easily become hermaphrodites (a plant with both male and female sex organs) which end up creating male flowers that create pollen which then “impregnates” the plant and others around it. The issue with stress-caused hermaphrodite plants is that most of the resulting seeds tend to be hermaphrodites too, so it’s not the best method to use and it also stresses your plants out quite a lot.

In order to turn a female plant male without stressing it out, all you need is some Silver Thiosulfate, also known as STS. If you apply STS to female plants it will modify their ethylene levels, which is the hormone in charge of determining the sex of certain plants. This causes female plants to change sex and turn into males without the disadvantage of male genes.

Silver Thiosulfate

Making your own STS only takes about 15 to 20 minutes and you’ll need two ingredients: Sodium Thiosulphate and Silver Nitrate, both of which can easily be found in any pharmacy. Sodium Thiosulfate is a neutral chemical salt that’s used to reduce side-effects in some cancer treatments and can easily be bought without a prescription.

Making STS

Caution:

You’ll need protective material such as gloves, safety glasses and a face mask; STS can be quite toxic when inhaled and it can leave large burns on the skin. Make sure you don’t use any metallic objects when making STS – everything should be plastic, as metal can alter the composition and reduce efficiency.

Process:

Do not use metal instruments or tools in this process. The first thing you’ll need to do is grab a plastic cup and pour in 20ml of distilled water. Next, depending on your chosen method, get either 7 Argenpal sticks or 0.35g silver nitrate. If working with Argenplal, dilute the tips delicately in the water (the tip is where the silver nitrate is). Grab another plastic cup and add 30ml distilled water and 1.3g of sodium thiosulfate, mixing it slowly until it’s fully dissolved. Then, mix the contents of both glasses and mix slowly again – make sure to use a plastic spoon, no metal.

The result is 50ml of pure Silver Thiosulfate, much too potent to use on your plants, so you’ll need to water it down a bit. Add your Silver Thiosulfate to 400ml of distilled water, so you’ll have around 450ml of STS. Make sure to shake quite a lot until it’s completely mixed. It’s still much too concentrated to apply straight onto your plants; take 100ml of the mixture you just made and add it to 400ml more of distilled water. You now have 500ml of a usable STS mixture that’s ready to be used on your plants.

Recommendation:

For maximum efficiency you’ll need to use it the same day you make it. If stored in a dark, cool space it can last up to 15 days but each day it’ll be a bit less potent. If you have it for over a week and haven’t used it we recommend making another batch if you want the best possible results.

How to use STS

STS is used by spraying it on your plants leaves, making sure that it’s entirely covered and dripping. We recommend taking the plant away from your growing area before beginning the process, or the mixture might end up getting on your other plants too. You’ll need to begin applying it 4 or 5 days after flipping the lights, right before your lights go off. This allows you to spray the plant without worrying about the light burning your plants. After 10 days, you need to respray your plants, using the same process, covering the plant in the mixture and letting it soak in in the dark.

The sprayed plant will begin growing male flowers with pollen with can then be used to pollinate whichever plant you want, causing seeds to appear that have absolutely no male genes in them. You can use the pollinated plant in order to make extracts from its resin; the amount of seeds it’ll produce will render it pretty much useless in as far as smoke-able flowers. The plant that you’ve applied the STS to will need to be thrown away, as it’s much too toxic to do anything with and if you consume any of it, even its resin, you could run in to some health issues.

When should you pollinate your plants?

In order to efficiently pollinate select plants, we recommend having two completely separate grow rooms or areas to work in. One should be for the plants that you’re planning on switching to male in order to obtain female pollen; the other should be specifically for the plants that you plan on pollinating once you’ve reverted the other ones.

When using the pollen that you’ve collected from your reverted plants, you need to make sure that the plant that you plan on using it on is fully ready for it; this can depend on the strain you’re growing. The right time to begin applying feminised pollen is actually right when your plants begin to flow real flowers.

You generally want to use the pollen as fresh as possible on a plant that is fully ready to take it on, or else it simply might not work – it’s kind of like people, in that sense. Certain things need to be just right. To harvest large amounts of high quality seeds, you’re probably better off doing a few tests in order to find out when the right moment is. You can do this by testing it out on the same strain before going big.

Make your own strains

When making your own seeds you can combine your favourite strains, resulting in a plant that you’ve created yourself that is 100% feminised. When you combine two strains, you’ll get various phenotype’s with varying qualities and structures. It’s important that you use regular seeds to do this, as feminised ones are much too weak and might have issues such as stress and end up becoming hermaphrodites.

In order to stabilise the genes in your resulting plants, you’ll need to select the phenotype you like the most, meaning that you’ll need to grow quite a lot of the seeds that you get from your feminised plant. Then, take a clone from each plant and set them to flower in order to study their characteristics. Once you’re done, you’ll need to pick two mother plants, revert them and cross them with each other to get a more balanced version. This process is repeated as many times as necessary in order to create a balanced strain that has the characteristics you’re looking for.

Feminising cannabis seeds is quite the process. You need to be able to keep perfect track and control of the timing when it comes to flowering and pollen yield if you want the best possible results. Take your time, do a few controlled tests and then you can start making large amounts of your own seeds.

Basic nomenclature of Cannabis genetics

What are IBL, S1, BX, F2 or landrace cannabis plants?

Often, when it’s time to buy cannabis seeds, the beginner grower can quickly become confused by some of the acronyms that are written next to the name of the variety. Simply by learning some basic concepts you’ll be able to make the correct choice between seeds with the same name, but different acronym.

There is a big difference between acquiring a second filial generation (F2) or an IBL, even if we talk about seeds of the same variety. These differences will condition the growth pattern of the plants, and also the final product, so that it is almost essential to learn exactly what is the meaning of these acronyms to be more accurate in choosing which seeds to buy, saving ourselves deceptions and getting closer to our preferences.

Pure varieties

Also known as landraces or purebreds, pure cannabis varieties have been the basis of cannabis breeding over the past decades. These species are endemic to a geographical area, where they have developed without having been crossed (hybridised) with other varieties. There are a large number of landraces from all around the planet, belonging to any of the three families of cannabis, C. sativa, C. indica and C. afghanica. Nepal is a good example; in this country different pure cannabis varieties (mostly narrow-leaved mixed use varieties) are grown and you can easily see the differences between genotypes based on the height above sea level at which they are cultivated.

Each variety expresses its genetic code (genotype) with a certain growth and flowering pattern (phenotype), so that pure varieties – with a purest genotype – show great uniformity, with just a few slight differences between phenotypes. We can expect very little variation between landrace specimens of the same variety, giving plants with very similar growth, organoleptic and psychoactive traits. Good examples of these varieties can be Hindu Kush (Sensi Seeds), Colombia Punto Rojo (Cannabiogen) or China Yunnan (Ace Seeds).

The IBL acronym (in-bred line), means that the cross was made using plants with almost identical genotype (inbreeding). On the contray, outbreeding is employed to introduce new genes into the variety. Although it happens naturally, self-pollination is a common technique used by breeders to fix desirable traits and thus stabilise the genetic line, either with landraces or hybrids. In cannabis genetics IBL seeds should present a highly uniform growth. Classic IBL examples are Skunk and Northern Lights (Sensi Seeds) or White Widow (Greenhouse). There is a lot of work behind IBL’s like these, as a large population of pure specimens had to be used to select the correct parents. In addition, the breeder must fight against inbreeding depression, the result of crossing parents with very similar genetic information. The reward for this job made properly is a highly stable seed variety.

If we make a cross between two different landrace or IBL lines (parental A and B) with different genotypes, the resulting offspring will be the F1 hybrid, the first filial generation from the cross of the phenotype #1 (Parent A) with the phenotype #2 (Parent B). Commonly in this kind of crosses we will observe a very uniform offspring, depending on how stable the parents are, of course. The F1 hybrid between two pure varieties or IBL’s will show the so-called hybrid vigour – also known as heterosis or outbreeding enhancement – introducing new genes that will produce “better” specimens.

Varieties like Orient Express (Ace Seeds), Red Afro (Tropical Seeds) or Eddy from Original Delicatessen would be good examples of true F1 hybrid. Thus, we refer to the first filial generation of any cross as an F1, while the term “F1 hybrid” is used when the parents are different landrace or IBLs.

When we cross two F1 individuals (whether landraces, hybrid or polyhybrid varieties), we obtain the second filial generation or F2, and so on with next generations, F3, F4, etc. The second filial generation often gives a more heterogeneous offspring than the F1; we can expect 25% to resemble parent A, 25% to resemble parent B and 50% will be a mixed expression of traits from both parents. As a consequence the stabilisation work must continue generation after generation ( F3, F4, F5…) until we find the generation that gives a uniform offspring with the traits that we are seeking.

Many of the seeds that we can find in shops are polyhybrids, crosses between different hybrids. The offspring of such crosses are in many cases quite unstable, producing plants with very different traits. Keep in mind that in these cases, the genetic mix is very varied, so we can not expect polyhybrid offspring to be as homogenous as an F1 hybrid. It’s easy to imagine how complex it can be to stabilise a cross, since we are mixing different genes from different varieties, which makes the selection and stabilisation process of the different traits a very hard work. The vast majority of hybrids on the market are in fact polyhybrids, like the White Russian (Serious Seeds) or Fruity Jack / Jack el Frutero (Philosopher Seeds).

BX or Backcross

Backcrossing is a common technique used by breeders to fix certain traits. This is done by crossing one of the progeny (F1, F2…) with one of the original parents (recurrent parent) which has the desired trait. To have an even more stable expression of the desirable trait, you can cross the BX1 again with the recurrent parent to have a BX2 (squaring) and so on with BX3 (cubing), BX4, BX5…

This technique is also used to replicate clones in seed form. It is done by choosing a male parent to cross with the clone only, backcrossing it as many times as needed to get an offspring as similar as possible to the original clone. The Apollo 13Bx (TGA Subcool) is an excellent example of this technique.

S1, feminised cannabis seeds

The acronym S1 refers to the first filial generation produced as a result of crossing the plant with itself. This is achieved by a range of techniques aimed at reversing the sex of the selected female plant, getting it to produce male pollen and using it to pollinate itself. If it’s done properly, we get feminised offspring with the same genotype of the parent used.

As always in genetics, the more stable the parent is, the more stable the offspring will be. This technique can also be used as a regular backcross, selecting and fixing traits but starting with just one parent. Thus, we can find S2 or S3 seeds, which have been backcrossed again with the original parent. Examples of S1 are Tropimango (Philosopher Seeds), S.A.D. (Sweet Seeds) or Trainweck (Greenhouse).