Cannabis Breeding Made Simple

Cannabis breeding is not as easy as pollinating your best Gelato female with pollen from your favorite White Widow male.. Although you would probably find some good “phenos” among the offspring, it would not be genetically stable (All the plants would be different from one another). Therefore you could not call it a strain. Then how could you create your own stable variety?

Some legendary strains such as the Haze, the Skunk#1 or the Blueberry took many years of hard work.
Although plant breeding can be very complicated, this post will aim at explaining the basics of cannabis breeding and make these concepts as simple as possible. 

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Basic Cannabis Breeding Terms:

Although we will keep it simple, there are a few basic terms that one must know in order to understand the concepts we will talk about in this article.

Genotype: This is the genetic makeup of an organism. it describes an organism’s entire set of genes. This is not something you can directly observe.

Phenotype: Also known as “Pheno”. A phenotype encompasses all the physical characteristics based on genotype. That is what growers can observe with their own eyes. For instance: Size, bud color, leaf shape… Note that the same plant can express different phenotypes based on the environment/growing conditions.

Alleles: The Alternative versions of a given gene are called alleles. Most cannabis plants have 2 different versions of each gene.

Heterozygous: having two different alleles of a particular gene or genes. Example: A plant that has 1 allele coding for broad leaves and 1 coding for narrow leaves may either produce broad leaves, narrow leaves or something in-between.

Homozygous: having two identical alleles of a particular gene or genes. For instance, a plant that has 2 alleles coding for purple flowers will produce purple flowers.

Why Make A Strain Stable?

For example, if you won the prestigious High Times Cannabis cup with a new “strain”, many growers may then want to grow that same outstanding strain. However, if that strain has not been properly stabilized, your chances of finding that same incredible plant from a 10 pack of seeds are slim to none.

In order to have uniformity among the offspring, it takes much more than a one-off cross.

Stability here refers to genetic stability meaning that the plants are homozygous for most genes. It is not to be confused with sexual stability (Having pure males and pure females without any hermaphrodites).

That being said, sexual stability is also an essential component. During the selection and stabilization process, plants must go through stress-tests in order to reveal their hermaphroditic tendencies. Then, all the “Hermies” must be culled out.

How Can You Stabilize A Strain?

There are several different methods breeders resort to in order to stabilize their strains.

Cannabis Plants by nature are diploids with twenty chromosomes. When you pollinate a plant, each one of the parents contributes ten chromosomes each to the new cell they have formed.


Selfing is a method that consists of pollinating a plant with itself (Generally a female plant). To do so, the breeder would have to reverse (Make a female produce male flowers) a branch of that female by spraying Colloidal Silver or Silver Thiosulfate (STS). Then, one can collect that female pollen and use it to pollinate the other branches of the same plant.
Selfing a female plant will only produce female seeds.
Each self’ed generation leads to an increase in characteristics by 50%. In other words, each time you self a plant, the genetic stabily (Homozygosity) will increase by 50%.
Selfing a cannabis plant is the fastest way to stabilize a strain. However, it is also the fastest way to lose vigor.

Cannabis Breeding Made Simple


Backcrossing consists of crossing a plant with one of its parents (The recurrent parent). Meaning that a chosen plant among the offpring will have to be crossed back with the same parent each time. By doing so, breeders can achieve offspring with a similar genetic identity to that of the chosen parent (Recurrent parent). This is how the breeder “Mr Soul” created the famous Cinderella 99 using an outstanding Jack Herrer plant as the recurrent parent.
The advantage of backcrossing is that unlike the selfing method, you can still work with both male and female plants at the same time.

The biggest disadvantage is that by using this method, breeders can only fix a trait if the recurrent parent is already homozygous for the gene coding for that specific trait.

Line Breeding (Inbred lines):

IBLs are strains that breed true for a certain number of traits. A true breeding strain will have only one main phenotype with very little variations. IBL plants also have a uniform genotype.
To create a true breeding strain, cannabis breeders have a specific list of traits they are after. Then, they work with large populations of plants in order to find plants that would express these traits. Once the breeder has found a male and a female (Or 2 females) that match his criteria, he will make seeds with them. Then, the same process starts all over again with the offspring. It takes several generations to create a true breeding strain. Generally at least 5. However, you cannot focus on too many traits at the same time because it is very unlikely to find several specimens expressing the same group of traits. The bigger the population a breeder works with, the more traits he or she can focus on at once. Although breeding requires skills and knowlege, it is also a numbers game!

A Slow Process:

Some Landraces are almost true breeding because they have been selected by farmers for certain specific qualities over many generations. On the flip side, polyhybrids require much more work in order to become genetically stable.  These are full of genetic diversity and genetically unstable. Therefore, it may require over 10 generations for a polyhybrid to become an IBL.
You can create an very stable line by inbreeding your plants, thus creating an inbred line (IBL). To create an IBL, one must keep records and cull out all the plants which don’t match his list of criterions.

Regular IBLs Versus Feminized IBLs:

Cannabis breeding is often a slow process. Nonetheless, line breeding is much faster and yields great results when working with female plants only. Line breeding using both male and female cannabis plants is trickier for 2 reasons:

  • It is often hard to know what female attributes a male can pass on. The best way to know is to grow each male’s offspring but this is very time consuming.
  • Male plants don’t “Herm” (turn hermaphrodite) as easily as female plants. For that reason, it is harder to stress-test them.

Line breeding for many generations leads to the creation of new IBL strains.

You can also cross 2 distinctly different IBLs to produce a new, uniform phenotype also known as a true F1 Hybrid.

True F1 Hybrids:

Many plant breeders and expert growers see True F1’s as the holy grail of breeding. True F1’s are sought after because the are both uniform and highly vigorous. True F1’s are the result of a cross between 2 stable lines (IBLs) that are genetically very different from each other. Despite the fact that both parents are very different, the offspring will look very stable.
Because each parent is highly homozygous, it always passes on the same version of a given gene to its offspring. That is why, all the true F1 plants that have the same parents will have almost the same combination of genes. That explains why true F1’s are very uniform even if they are heterozygous. Furthermore, true F1’s are more vigorous than either parent because of the principle of Heterosis (Hybrid Vigor). Having 2 different alleles for each gene is what causes that incredible Hybrid Vigor.

F1 Hybrids:

Just like true F1s, F1s are the offspring of two genetically different plants. However, unlike true F1s, the parents of an F1 do not have to be genetically stable (IBL) for making an F1.
Unlike true F1’s that are created using 2 very stable lines, F1’s are often very unstable. Because their parents are not homozygous but heterozygous. As a result, there will be many different combinations of genes among the offspring. Although F1’s are generally vigorous, there won’t be one main pheno but many. When we talk about pollen chucking, we refer to the creation of F1 Hybrids. These are your typical “One-off crosses”.

F2 Hybrids:

F2s are the result of the combination of 2 F1s. These are the most unstable of all hybrids. Nonetheless, that incredible genetic diversity can be very interesting for pheno-hunters and breeders looking for a stand-out specimen.

Inbreeding Depression:

When creating a true-breeding strain, plant vigor sometimes decreases to the point where breeders have to either backcross, or go back one or several generations in order to regain some vigor. That is because when plants become too heavily inbred, they become genetically weak and they grow much slower. By the same token, genetically weak plants can develop undesirable mutations. Selfing a cannabis plant is the fastest way to stabilize a strain but it is also the fastest way leading to inbreeding depression.

Can Home Breeders Achieve Great Results?

While it is true that professional cannabis breeders are more likely to create good stable strains, home breeders can definitely create new outstanding varieties as well.
As mentioned before, cannabis breeding does not only take skills and knowledge but it is also a numbers game. For that reason, home breeders would have to focus on only one line at a given time. They can optimize their grow space and use small containers to maximize the number of plants. With the right experience, a lot of discipline and a great deal of patience, home breeders can also obtain amazing results.

The world of cannabis breeding is full of surprises and anyone with a solid breeding strategy has the potential to create the next Skunk#1…
If creating a new strain seems daunting to you, don’t be afraid, take it step by step and be patient.
Good luck with your future breeding endeavors!!