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Cannabis Breeding Methods: Line Breeding

Line breeding is the most famous method serious cannabis breeders resort to in order to create stable strains. You already know how to grow great cannabis, would you now want to create your dream strain? If so, you have come to the right place. In this tutorial, you will learn more about how to stabilize certain specific plant traits in order to create a true IBL!

What Is An IBL?

IBL is an acronym which stands for In-Bred Line. Just as many dog breeds are IBLs, so are some cannabis strains.

IBLs are strains that breed true for a certain number of chosen traits. These true-breeding varieties look very uniform and although they are never as uniform as clones, they express very little variations. A true breeding strain will have only one main phenotype (Observable physical characteristics). IBL plants also have a uniform genotype (genetic makeup of an organism ).

You don’t have to have an expensive breeding software to get started! A simple Excel spreadsheet will do.

Line Breeding Is A Numbers Game

The goal when creating a new IBL cannabis strain is to first isolate and then stabilize some unique characteristics. It can be a unique terpene profile, a unusual cannabinoid ratio,a short flowering time an outstanding bud color… No matter what it is, it is possible to develop a strain that will breed true for a certain number of specific traits. For that, you have to first establish a list of traits you wish to select for. Keep in mind that the more traits you want to fix, the more plants you will have to work with and the longer the process is going to take.

Indeed, it is pretty rare to find a specimen that expresses all the characteristics you are looking for. However, the more plants you sift through, the higher your chances of finding the holy grail!

There are 2 ways to go about it:

Option 1: Establish a specific list of traits you are looking for beforehand and go through a large population in order to find a plant that combines all these traits.

Option 2: Grow out a large number of plant until you find an outlier you really like. Then, use that plant as your starting point.

Regular Or Feminized IBL?

Would you want come up with your own regular or feminized true breeding strain? To help you make that decision, let’s weigh the pros and cons.

Regular In-Bred Line


  • The pollination process is easier.
  • Better for preserving the strain (easier to perform a reproduction run with).
  • Maintains the possibility of having a regular and a feminized version of the same strain.
  • Produces more seeds. (Reversed females yield much less pollen).


  • Higher risk of hermaphroditism: Male plants don’t always reveal their hermaproditic tendencies.
  • Longer and harder to stabilize (both genetically and sexually): It is often hard to know what female attributes a male can pass on.
  • Can easily be copied: Growers don’t have to reverse the females in order to make seeds. They can just use a male plant.

Feminized IBL


  • Lower risk of hermaphroditism (Female plants are easier to stress-test).
  • Faster to stabilize (both genetically and sexually): Since the female traits are directly observable on female plants, it is easier to find 2 identical females thus fixing the desirable traits faster.
  • Harder to copy. Because making fem seeds using 2 females is a trickier process, not every grower can make more seeds.


  • It is harder to reverse a female: Some female plants are sterile or produce very little pollen. Breeders also have to start reversing their plants at the right time (Usually 1 week before flipping the other female to flower).
  • The variety is more likely to disappear since making seeds becomes trickier.
  • Breeders no longer have the option of having a regular and a feminized version of the same strain.
    Produces fewer Seeds.

Chosing The Right Genetics

The goal when line breeding is to work a particular line, to stabilize attributes that are truly unique.
Therefore, you may want to start your project with strains that you really like or rare landrace seeds.
Landraces are the indigenous varieties of cannabis from which all the modern strains descend. Altough landrace strains are often fairly homogeneous in terms of growth pattern, they can express a wide array of terpene and cannabinoid profiles. By breeding with these foundation strains, it is possible to create a new IBL that will be very different from most modern varieties.

Moroccan Sativa

Get Started Line Breeding

There are 2 different ways you can start working your line/lines.

1) You can either start line breeding right away by isolating a specific phenotype of landrace strain or strain with a high amount of diversity such as an heirloom variety. This is the fastest way to create an IBL but the diversity of phenotypes to choose from may be limited.

2) You can outcross 2 hybrids or 2 landraces and then work the line. The F1 generation will be more or less uniform according to the homozygosity of the parents. Homozygous: having two identical alleles of a particular gene or genes. For example, a plant that has 2 alleles coding for red stems will produce red stems. However, the F2 generation will express all the possible genetic combinations. Meaning, breeders will have a very high diversity of phenotypes to choose from. This is where the big pheno hunt takes place!

Breeders like to work with F2s because they are genetically unstable. F2s have a high genetic diversity and express many different phenotypes.

A Slow Process

If you want to create a feminized strain, you will simply have to chose 2 similar females that express the traits you are looking for. If you wish to create a regular strain however, the process will be more complicated. You will have to grow out the offspring of each of the potential males you’ve chosen. That way you will know which one passes on the female attributes that best match those of the females you selected. Once you have picked your ideal parents and made some seeds, repeat the process with the offspring. Do this at each generation until the plants breed true for the specific traits you want to fix.

The Keys To Success

ALWAYS thoroughly Stress-test the parents you want to use for creating your IBL as it needs to be both genetically and sexually stable.
ALWAYS keep the seeds from the previous generations in case you fix undesired traits by mistake or in case you notice a sharp loss of vigor (Inbreeding depression).
ALWAYS be consistent, select for the same traits generation after generation until you achieve homozygosity.

How Long Will It Take?

There is no short answer. You will have to keep going until the plants look uniform, have a similar taste, smell, effect…
But on average it takes 5 to 9 generations to create an IBL.
If you started with a landrace or heirloom and worked a feminized line, it may only take 4 to 5 generations. If, on the other hand, you are creating a regular strain and started with a polyhybrid, it could take up to 9 or 10 generations.

Line Breeding Hourglass


Patience is key here. After working on the same project for several years, it may be tempting to want to give up and move on to something else. However, if you resist the temptation and keep at it long enough, you will have achieved something very few growers have done! You will have in your possession, your dream cannabis strain in seed form.
True-breeding strains are rare and highly prized. With it, breeders can create many True F1 hybrids (The holy grail of breeding).
The goal of this tutorial was to keep things simple enough so that new breeders can get started.

Hopefully, this practical guide has given you a good head start in your next cannabis breeding project! Best of luck!!