how to stabilize a strain

Breeding And Preserving Cannabis Genetics At Home

If you’re interested in breeding your own cannabis strain but find scientific jargon confusing, and graphs and punnet squares put you to sleep, this is the blog for you. We break down all you need to know about breeding marijuana at home and how to preserve those precious fire clone-only genetics. Practical advice without the academic speak.



Breeding cannabis and continuing a lineage in seed is not the exclusive preserve of the experts. Home growers that have acquired high-level cultivation skills and mastered the essential techniques can easily transition from grower to breeder. Creating F1 seeds and hybrids is very doable. Most of the cannabis strains that have become legends were created by home growers. On occasion even by accident.

While it might not be possible to build your own seed bank from the grow tent in the spare bedroom. Small-scale breeding is a viable option. You don’t need a masters degree in botany. Just good old-fashioned dope growing experience will suffice.

Time in the grow op will have already given you a keen eye for pheno hunting. Plus you have developed the hands on cannabis tradecraft skill set to succeed.



Taking cuttings from cannabis plants is a great way to preserve a strain. Sometimes prized varieties are available in clone-only form, and the grower has little option other than continuing to take cuttings in order to preserve the genetics.

Cloning is a transferable skill and even more essential to cannabis breeders than growers. You need to have a consistently high success rate with cloning as a prerequisite to breeding.


F1 seeds can be produced with just a female marijuana clone. These seeds carry only the genetics of the mother. In order to accomplish this, the grower must reverse the sex of the female to induce self-pollination.

Most home breeders will purposefully stress the flowering female to produce a few seeds. Selfing is commonly applied to clone-only marijuana varieties to convert it to F1 seed form.



Ok, so if you are happy with a batch of regular cannabis seeds. Perhaps you want to make use of the males? Well, you can cross cannabis from the same batch. Assuming you are familiar with the strain and cropping from the same pack of seeds you can potentially select a breeding pair to cross.

This is an old school ganja farmer’s method mostly applied outdoors. Although, breeding from the same batch has potential indoors provided the original organic seeds are genuine. If so, not only will the resulting progeny be more or less stable but you will have saved cash on seeds for the next crop.

Before further breeding experiments, it’s no harm to practice collecting pollen and making seeds first. Breeding from a reliable batch is a good introduction to cannabis breeding.


A polyhybrid is simply a strain that results from crossbreeding two hybrid strains. When different landrace or inbred strains are crossed, this results in an F1 hybrid, a term used to label the first generation derived from the cross. F1 hybrids become F2, F3, and so on, as new generations are created via inbreeding.

However, if an F1 hybrid cultivar is bred with an F1 hybrid cultivar from a different genetic line, a polyhybrid is formed. F1 hybrids already possess varying genetic traits from both parent strains, meaning polyhybrids are even more diverse and unpredictable in the traits they possess. Creating polyhybrids is a great breeding method as it allows you to combine unique traits from a wide spectrum of cultivars. Although, as you can imagine, these strains are quite unstable and heterozygous. It takes some solid work to stabilise these varieties and ensure that their offspring are more uniform.


Breeding cannabis requires quite a lot of space. You need a nursery and propagation area and different rooms for male and female specimens to avoid unwanted cross-pollination. Even more space is needed if you intend to start breeding polyhybrids over multiple generations starting with four inbred cultivars. If you intend to begin this process, you’ll need to learn how to pollinate your flowers in the correct way.

Seeing as you’re considering breeding, you are probably already well aware of this fact, but it’s always worth reiterating: Keep your males away from your females! This is especially important when looking to breed a polyhybrid because of the increased chances of breeding the wrong varieties together.

First off, you’ll need to collect pollen from male plants when the time is right. Pollen is ultimately plant sperm, and is needed to fertilise female flowers to make them produce seeds. When the male pollen sacs have opened, place a sealable bag over the plant and give it a shake.

Female plants are ready for breeding during the early flowering phase when small, white pistils start forming. These “pre-bud” structures are basically little hairs that protrude from the calyx to catch pollen. Next, isolate the chosen female plant to further prevent any unwanted fertilisation. Consider setting up a specific fertilisation area to avoid any mishaps.

To pollinate female plants, place the pollen bag over branches that show bud formation. Seal the bag over individual branches and shake again. Leave it there for around 1 hour and repeat the process with each branch that bears buds.

It’s vital to document everything you do when breeding cannabis, especially during the more complex process of creating polyhybrid strains. It’s easy to mix up genetics and lose track of which male you bred with which female, and what strain each of them is. It’s best to label every plant individually so they can be easily identified. It’s also a good idea to create a spreadsheet or draw out a flowchart on a whiteboard to keep track of every cross you’ve made with each individual plant. Add dates beside every documented task to help you estimate waiting periods accurately.


Genuine F1 Hybrids are the jewels in the crown of the Royal Queen Seeds catalogue. The cold truth is creating fantastically potent, productive and vigorous growing F1 hybrids is a long term process. Professional breeders invest years of their lives into breeding projects and select cultivars from hundreds if not thousands of cannabis plants.

Genuine F1 hybrids can only be derived from crossing pedigree stabilised or landrace strains. They express genuine hybrid vigour. Unless you’re planning a strain hunting expedition, tracking down heirloom landrace seeds is hard graft. It’s probably more convenient to stick with the RQS catalogue for awesome hybrids.

Similarly, filial breeding can be complicated. Honestly, it’s far too demanding for the first time home breeder. By crossing a pair of F1s (first generation) the resulting progeny is the F2 (second generation). Unfortunately, these seeds will be far less stable and far more difficult to work with than the previous F1 generation.

Careful selective breeding in large numbers is required to succeed with this approach. Often it takes multiple generations of breeding perhaps until F5 (fifth generation) or even F6 (sixth generation) before the line can be stabilised.


Have you ever purchased the same cannabis strain multiple times and noticed that it looked completely different each time? Maybe it even tasted slightly more sweet or sour than before. Or maybe you’ve grown the same strain repeatedly and realised how different one plant looked from the next? These differences within the same strain are referred to as genetic variability. Even though plants share the same lineage, their unique genetic expression, or phenotype, is a result of how their genetics respond to the environment.

Differences in phenotypes can manifest as variability in size, resin production, colour, and so on. Strains can also vary in their chemotype. This refers to the chemical constituents that they manufacture. One plant might have higher levels of a specific terpene, whereas another may have slightly higher levels of CBD. If you germinated a bag of seeds that all shared the same lineage and noticed a large difference between the phenotype of each plant, this would mean that the strain is unstable, and that the seeds are heterozygous. Although this isn’t necessarily an issue for hobby growers, it can become problematic for commercial growers looking for strict consistency among their crop.

This consistency is possible, and can be achieved by stabilising the genetics of a strain. This will then produce seeds that are more homozygous, featuring significantly less variability between phenotypes. But how can breeders go about stabilising a strain?

One way to achieve this is called backcrossing, also known as “BX” within the cannabis breeding lexicon. When breeders are aiming to create a new strain, they select two parent strains with desirable traits. Upon crossing them, the first generation is created. Backcrossing essentially refers to taking a member of this generation back up the family tree to breed it with one of its parent strains. This type of inbreeding helps solidify the presence of one of the parent’s genes as they are bred together repeatedly.

For example, if the female parent strain was particularly high in CBD and myrcene, thus producing a calming effect, by breeding her with one of her male offspring that also shares some of these traits, the plants of the next generation would be even stronger in those traits. This is because they will contain more of her genetic material than the original generation that was also influenced by the male parent.

Although backcrossing is a tried and tested way to stabilise cannabis genetics, excessive backcrossing can cause some issues. By inbreeding plants to such a degree, any recessive genes that produce undesirable traits will also be strengthened and passed down to all plants of subsequent generations.

As you can see, there are quite a few ways to preserve your favourite strains, and turn them into new strains of their own. This guide is meant to give you a good general overview to get you started, before delving into the more complicated aspects of it.

If you have an amazing strain you want to preserve you need to read this blog. Lets talk about breeding your own weed strain.

F1, F2, P1 + how to stabilize your F1s

Well-Known Member
Well-Known Member

I ran across this a few days ago and thought i’d share it with those of you who either always wondered or maybe need a refresher course

What really is an F1 cross?

Well defining the terms P1, F1, F2, homozygous, and heterogygous can be a simple task,
however, applying them to applied genetics can often create confusion. Depending on
your point of reference, a plant could be described as any of these terms. For our specific
field of interest it’s important to further define these terms to reduce confusion and protect
the consumers. First I’ll provide the classic scientific definition of these and other related
terms and then I’ll dive into each term into detail.

Heterzygous – a condition when two genes for a trait are not the same on each member of a pair of
homologous chromosomes; individuals heterozygous for a trait are indicated by an “Aa” or “aA” notation
and are not true breeding for that trait.(Clarke)

Homozygous – the condition existing when the genes for a trait are the same on both chromosomes of a
homologous pair; individuals homozygous for a trait are indicated by “AA” or “aa” and are true breeding
for that trait. (Clarke)

– Now the heterozygous and homozygous terms can be applied to one trait or a group of traits within an
individual or a group of individuals. Depending on your point of reference, an individual or group can be
considered both homozygous or heterozygous. For instance, say you have two individuals that are both
short (S) and have webbed leaves (W) and have the following genotypes.

#1 = SSWW
#2 = SSWw

They are both homozygous for the short trait but only individual #1 is homozygous for the webbed leaf
trait. Individual #2 is heterozygous for the webbed leaf trait and would be considered a heterozygous
individual. As a goup, they would be considered heterozygous in general by some and homozygous by
others. It would depend on your point of reference and the overall importance you place on the webbed
leaf trait. Most would consider it to be heterozygous.

For example, the blueberry cannabis strain is considered a true breeding homozygous seed line because
as a whole the many offspring have a similar look and produce a similar product. However there are
often subtle differences between the plants of characters such as stem colour and potency. When taking
a close look at blueberry, you will find heterozygous traits, but because of the whole overall look, we
still generally consider them homozygous for the purpose of breeding programs. Using dogs is another
way to explain this, take a dobie for example, you can tell the difference between dobies, but you can
tell a dobie from another breed. Ya follow?

Hybrid – An individual produced by crossing two parents of different genotypes. Clarke says
that a hybrid is a heterozygous individual resulting from crossing two separate strains.

– For the purpose of seedbanks, a hybrid is in general, a cross between any two unrelated seedlines.

F1 hybrid – is the first generation of a cross between any two unrelated seedlines in the creation of a
hybrid. F1 hybrids can be uniform or variable depending on the P1 parent stock used.
F2 hybrid – is the offspring of a cross between two F1 plants (Clarke).

What Clarke and other sources don’t make clear is do the two F1’s need to be from the same parents? By convention they don’t. As
well, german geneticists often describe a backcross of an F1 back to a P1 parent as a F2 cross.

– OK lets say we take blueberry and cross it with romulan (both relatively true breeding of their unique
traits) to create the F1 hybrid romberry. Now lets cross the F1 romberry with a NL/Haze F1 hybrid.
Some could say this is a F1 cross of romberry and NL/Haze. Others could argue that it is a F2 cross
of two F1 hybrids. Gets confusing doesn’t it? Now lets cross this Romberry/NL/Haze(RNH) with a
Skunk#1/NL#5 F1 hybrid to create RNHSN. Now some would argue that RNHSN is an F1 hybrid
between RNH and SK/NL seedlines. Others would call it an F2.

– So what does this mean to the consumer? It means that a seed bank can call a cross whatever it wants
until the industry adopts some standards. This is what this article will attempt to initiate. Clarke eludes to
standardising these definitions but never really gets around to it. Fortunately other plant breeding
communities have (Colangelli, Grossnickle&Russell, Watts, &Wright) and adopting their standards
makes the most sense and offers the best protection to the seedbank consumer.

Watts defines an F1 as the heterozygous offspring between two homozygous but unrelated seedlines.
This makes sense and gives the F1 generation a unique combination of traits; uniform phenotype but not
true breeding. This is important in the plant breeding world. This means that when a customer buys F1
seeds that they should expect uniform results. It also means that the breeder’s work is protected from
being duplicated by any other means than using the original P1 (true breeding parents). [There are
exceptions to this by using techniques such as repeated backcrosses (cubing the clone)]

F2 crosses are the offspring of crossing two F1 hybrids. This means that they will not be uniform nor
will they breed true. However, F3, F4, F5, etc will also share these characteristics, so to simplify
terminology for the seedbanks and seedbank merchants, they can all be classified as F2 seeds in general.
What does this mean for the preceeding example? Well, the blueberry, romulan, skunk#1, NL#5, and
haze were all P1 true breeding seedlines or strains (another term that needs clarification). Romberry,
NL/Haze, and SK/NL were all F1 hybrids. Both the Romberry/NL/Haze and the RNHSN would be F2s.
Within each group the consumer can know what to expect for the price they are paying.

Few cannabis seedbanks (if any) and their breeders are following these definitions and are subsequently
creating confusion within the cannabis seedbuying community. This is a change that needs to happen.
Note: this is a rough draft to be published to the internet. Hopefully in time it or something similar will be
used to help establish an industry standard. Any comments and critism is welcome to aid in the
production of the final draft. Small steps like this can only benefit the cannabis community over the long

This thread is about crossing your plants, and then stabilizing them!