Backcross Breeding Cannabis: What is It, And How to Do It?

Why backcrossing is vital in the creation of new strains


The number of different marijuana strains in existence is probably in the thousands at this point. It is all too easy to get bogged down in detail when trying to examine marijuana terminology, especially when breeding weed. If you ever go to a cannabis strain database, you will probably be confused as to what a specific strain is a ‘cross’ of, whether it is a hybrid, or else you won’t know what backcrossing means.

First of all, a hybrid is created through the breeding of two or more strains. These hybrids are a cross of these strains; and the strains you use to breed the hybrid are the parents, while your new strain is the offspring. For example, Blue Dream is a hybrid of Blueberry and Haze; these strains are Blue Dream’s parents.

Now that marijuana is legal medicinally or recreationally in 33 states, breeders have more freedom to experiment. They can now focus on breeding to strengthen and purify strains, combining the desirable characteristics of strains, and enhancing traits such as potency and yield.

Breeding Marijuana

Before we delve into further detail on backcrossing, let’s provide you with a 101 on breeding. First of all, make sure you know where the seeds came from. If a seller is unable to tell you the origin of the seeds and their genetic profile, it is best if you conduct business elsewhere.

The great thing about breeding weed is that you can do it at home. As you know, the marijuana plant can be male or female. Your focus should be on females because they are the only gender that produces resinous buds filled with THC. Males are required for pollinating the females.

Going back to Blue Dream. At some point, a breeder decided that they liked certain traits of the parent strains, Blueberry and Haze, and decided to combine the two to create a new marijuana strain. To complete the process, the breeder needed a male of one strain and a female of the other. Next, the breeder ensured that the male pollinated the female. The seeds were harvested, grown separately, and in the end, the breeder ‘gave birth’ to a new hybrid.

As for deciding which strain should be the male and which should be female, consider what you are looking for from your hybrid. Typically, the characteristics of the female carry over to the seeds more than male traits. Ideally, you will choose a male plant that complements the characteristics of the female plant.

Once you have identified the strains you want to use for breeding, and have the requisite male and female plants, the next step is to place several females and a male into a special breeding chamber to ensure the pollen is contained. This may sound complicated, but you can create a DIY chamber by finding a suitable space and keeping it enclosed with the aid of plastic sheeting.

Genetically speaking, it makes more sense to only have a single male plant for breeding because one is enough to pollinate 20 or so female plants. This is called ‘intentional’ breeding. Spare a thought for the unfortunate growers who accidentally pollinated an entire crop of females with a male when all they wanted was some resinous weed.

Once the plants are in the chamber, you have the option to keep them in the vegetative stage for a couple of weeks to boost their size. Alternatively, you can go right ahead and force them into flowering using a lighting schedule of 12 hours of light/12 hours of darkness each day. A few weeks into flowering, the male will grow pollen sacs which release the pollen. It lands on the females, and the pollination process is complete.

The enclosed chamber is important because the last thing you need is for pollen to spread to your cannabis garden and pollinate all your females. If you are not satisfied, you can always shake the male plant so that pollen spreads. Once pollinated, the females continue to flower and grow seeds and buds. The seeds are a hybrid of the male and female plant’s genetics.

Once you have mature seeds, you harvest and dry them. You can now finally grow the seeds on their own.

Achieving Consistency When Breeding Marijuana Plants

If you have ever purchased a hybrid strain from a dispensary, you should appreciate the effort that has gone into ensuring your weed has consistently desirable traits. In all likelihood, the weed you buy has gone through generations of breeding to ensure it doesn’t carry unwanted characteristics.

The seeds created from cross-pollination will have different attributes to their parent strains. Every seed is unique with various characteristics and different combinations of traits derived from its parent. Seeds with different expressions of traits are known as phenotypes. If you purchase cannabis seeds, the best kind is ‘homozygous’; that means they have the same set of genes.

When you have homozygous seeds, you know that your plants will consistently produce seeds with the same genetic makeup every time. This consistency is highly desirable because it means breeders and consumers know what to expect 100% of the time. Heterozygous seeds produce a wide variety of phenotypes which makes them a lot less predictable. When you cross a strain, you need to select the phenotype you prefer.

What is Backcrossing Marijuana?

Backcrossing is also known as ‘BX’, with ‘B’ meaning Back and ‘X’ meaning Cross. It is a form of breeding that allows a targeted characteristic to pass from the parent to the offspring. Backcrossing is different from typical breeding methods because there is only one parent plant along with the offspring.

When a breeder has crossed a strain and determined the most desired phenotype, he will backcross the strain to make its genetics stronger. The process involves cross-pollinating the new strain with a parent or with itself. In effect, you are inbreeding the strain. This process ensures the strain is more homozygous and strengthens the desirable traits and genetics. Moreover, the genes get passed down to the next generation, and then the next one, and so on.

If you decide to backcross a strain, make sure you don’t overdo it. If you inbreed a plant too often, recessive genes can become apparent in the offspring. Ideally, you will not perform backcross breeding more than twice. Also, you will normally choose the best male plant to be bred back to the parent.

Within five generations of breeding the hybrid to the parent, the plant should have the traits you are looking for. When this happens, you can breed a female and male stabilized hybrid together to create a new hybrid.

Final Thoughts on Backcrossing & Breeding

If you are planning to breed cannabis, please note that it takes a lot of time and patience. Occasionally, the offspring will prove disappointing, and you shouldn’t expect to find the ideal seeds after a single cross.

It will take several attempts and failures before you finally see the fruits of your labor. Even when you find the ‘perfect’ phenotype, it will be necessary to complete a backcross or two to stabilize the genes and reproduce the strain in seed form. However, if you have the time, patience, and cash, breeding marijuana can be a lot of fun and really help you learn more about this wonderful plant.