How to Crossbreed Cannabis Plants? [Guide]

The precise number of cannabis strains in the world is unknown, although it is likely to exceed 1,500. It is a number certain to increase exponentially in the next decade or so, now that medical marijuana is legal in two-thirds of American states and is fully legal in Canada.

If you look at strains from the 1970s and again at what is in your local dispensary today, there is no comparison. Today’s weed consistently contains a higher percentage of THC, the psychoactive compound that provides you with the all-important ‘high.’ Perhaps the main reason for the explosion of potent weed strains is a greater ability to grow.

Remember, most marijuana grows ‘back in the day’ were clandestine affairs. Now, numerous states allow home cultivation. As a result, intrepid growers are busily trying to create the next great strain. Believe it or not, many of today’s most popular strains were conceived in someone’s relatively small grow room. These strains were achieved through ‘crossbreeding’, which means combining the genetics of two or more marijuana strains.

Results May Vary

There is a suggestion that all marijuana strains are the same – which is complete nonsense. Lab testing alone will confirm differing levels of cannabinoids, terpenoids, and flavonoids from one strain to the next. What you might not be prepared for is the differences between the same strain!

Most cannabis users have found a variety they enjoy, but are often surprised by the lack of consistency in the strain. There are several reasons why this is the case. Growing environment and techniques, along with lighting, will change the final outcome. However, the real reason for the inconsistency lies in cannabis genetics and breeding.

Marijuana is a plant but bears no resemblance to other garden favorites such as the tomato plant in terms of growing consistency. If you’ve ever grown tomatoes from seed, you’ll notice that you typically end up with fruit that has a similar size and flavor each time. This glorious consistency is notably absent from weed seeds.

The majority of garden food crops are ‘monoecious’, which means each plant has male and female organs. Marijuana plants are ‘dioecious’, which means they consist of separate male and female plants. As you know, female plants are grown for their THC-laden buds, while male plants are used to pollinate females to get seeds.

As it is a dioecious plant, you have to pollinate the female with the male. The resulting seeds from what is known as ‘cross-pollination’ represent a far greater genetic variety than self-pollinating plants such as tomatoes.

As a consequence, crossbreeding marijuana plants is a lengthy, unpredictable, and utterly frustrating experience. Many breeders begin with a clone-only strain and try to develop a seed-based strain that has the traits of one of its parent plants. If you go down this route, expect a different result with every seed. It is normal for breeders to sprout well over 100 seeds from a single variety to find the ‘true’ representation of what they sought.

In most cases, breeders are seeking to create a ‘hybrid’ strain which is a stable genetic line. If you have read our strain reviews or growing guides, you’ll have noticed that the vast majority of commercially available strains are hybrids. Before you embark on your quest to create the next great hybrid, please note that it can take more than 1,000 seeds to find what you’re looking for. Sure, you can sprout a few seeds and sell them under a popular strain name, but they are unlikely to be the strains you initially wanted.

Worldwide Weed Grown in Your Home

If you are a marijuana grower today, you are very fortunate to live in an age where there is an enormous range of genetics to choose from. Dedicated growers traveled the world to find landrace strains which we now use to breed our own strains. For the record, a ‘landrace’ strain is one that was developed by residents.

Growers visiting regions such as the Hindu Kush Mountains would have been greeted with strains of cannabis with traits they had never seen before. They brought back dozens of seeds and evaded law enforcement in the process! Next, they mixed the seeds with other breeding stock to grow ‘new’ strains that had many of the traits found in the landrace strain.

The often ignored ‘Ruderalis’ plant is a prime example of a marijuana plant that became mixed into numerous breeding programs. Although the Ruderalis was small and thin, it could grow in inclement weather. The buds were not especially potent but their ability to auto-flower within a few weeks, regardless of lighting schedules, made these plants a hot commodity.

In this scenario, the Ruderalis plant by itself was not something most breeders wanted to grow due to the small buds and low THC levels. However, by crossbreeding Ruderalis seeds with high-THC genetics, it was possible to create an auto-flowering strain with a medium to high THC content. Eventually, growers were able to ‘breed out’ the phenotypes that didn’t produce large buds.

Crossbreeding – Desirable Traits

Successful cross-breeding involves selecting ‘parent’ strains with the best traits and crossbreeding them until they achieve the ideal blend of both parent plants without the associated negative characteristics. It is NOT something you can get right the first time. Indeed, it will probably take multiple generations of plants, and several years, before you perfect the art of crossbreeding.

Remember, every marijuana plant is a bit different, and when you grow a seed, the seedlings will have a combination of traits from both parents. Eventually, you could end up with weird, unique, and wonderful new strains. Quality genetics is always the first step so here are the traits to consider when selecting strains for breeding:

  • Buds: Look at a plant’s THC or CBD levels, overall potency, color, smell, aesthetics, and perceived effects. The issue here is that when you focus on one trait, you pay less attention to others. For example, if you focus on getting a purple color, you don’t have full attention focused on how the plant affects you.
  • Growing patterns: Is it short and bushy or tall and skinny? How long is the flowering stage? What kind of yield can you expect? To do this, observe the plant while it is growing.
  • Durability: How quickly do the plants grow? Is it highly resistant to mold and pests? Does it have strong stems? How does it handle hot and cold temperatures?

The larger the genetic pool, the easier it is to find the right traits. Unless you have a commercial operation, it is unlikely that you can grow more than a few plants at a time. There is also the small matter of obeying the laws in your state! As you breed together plants from differing strains, you can create new strains that carry interesting traits from their parents.

What is a Phenotype?

In simple terms, a phenotype is a plant’s genetics and its environment. It is a list of the traits you see in a plant. For example, you may have a strain with a ‘short’ phenotype. They are similar to the traits kids get from their parents, and every child is a different phenotype. For example, if both your parents are tall, you are likely also to be tall. If you have one short and one tall parent, you could be tall or short, and your siblings could be much taller or shorter than you.

Stabilized Strains

Unstabilized strains often carry several phenotypes, which means that two plants of the same strain are likely to exhibit different traits. Stabilized strains display the same phenotype, which means plants of the same strain will grow in the same way. You can achieve this by manipulating your genetic stock through breeding and back-crossing until you end up with parents that consistently produce offspring that grow the same. This is essentially cloning in seed form.

Back-crossing involves taking a plant and crossing it with one of its parents or a close family member. This inbreeding helps create offspring with genetic similarities to the chosen parent. Every offspring plant created through back-crossing will probably carry two versions of the chosen parent’s genes.

By the way, don’t ignore growing environment when breeding. A clone of a plant is a genetic copy of the original and will grow the same when exposed to the same environmental conditions. However, despite being a clone, the plant will NOT grow the same if you expose it to different conditions to what the original plant grew in.

A Quick Overview of Crossbreeding

Hopefully, you now have a better idea of what crossbreeding entails, and the likely outcomes. The first step is to choose your female and male plants. When choosing a female, simply grow your weed as normal and if a female plant has nice, fat buds, grows well and is generally healthy, keep it.

Finding ideal male plants is less simple. The only proven method is ‘trial and error.’You need to breed a male plant with different females to see the kind of offspring they produce. Eventually, you will find a male plant that offers desirable traits to the offspring.

Once you have the male and female plants, keep them separate during the growing process. Always ensure that males are separated from females as soon as the small pollen sacs on males (their pre-flowers) show. Otherwise, the males will pollinate the females, and you end up with unknown genetics.

Pollen Collection

When the pollen sacs are well developed, begin collecting the pollen. An easy method is to place an open Ziplock bag around the stem and shake it. The pollen will fall off and go into the bag. If you aren’t using the pollen immediately, save it and store in the freezer. Make sure you use it within a month. Also, make sure you shower and change clothes after visiting the males because pollen sticks to everything!

Pollinating the Female Plants

The females are ready for pollination a few weeks after displaying signs of white pistils. There will probably be buds forming at that stage, but the pistils should still be white (they begin to turn a red or brown color when harvest time approaches). Isolate your chosen female from the rest of your crop and switch off your grow room’s fans.

Place the bag of pollen over a stem which has several buds growing. Shake the bag to ensure the buds get coated with pollen. Cover the site with the bag for a couple of hours and shake it again to get the last bits of pollen out. Leave the bag on the site for a few more hours and remove it carefully.

Add Nutrients

The female plant is now a ‘mother’ plant and needs extra nutrients, including additional Nitrogen. In fact,it is a good idea to use a vegetative stage feeding schedule. Seeds should begin to form a couple of weeks later and will burst through their calyxes a few weeks afterward. If you need to store the seeds, put them in a cool, dark place but DO NOT freeze them.

Plant Your Seeds

Germinate your seeds in the usual manner and take notes on how they grow. This means keeping a journal which highlights details such as flowering time, potency, color, taste, and scent. If you’re feeling confident, keep clones of all the plants in case one of them turns out to be exceptional.

Final Thoughts on Crossbreeding

While it isn’t difficult to begin crossbreeding, it is extremely hard to create a fantastic new strain. In reality, it will take hundreds of seeds and several years to find your ‘ideal’ hybrid, but if you get lucky, maybe you will strike it rich!

No matter what, make sure you keep detailed records and test your plants regularly. Be kind and alert other growers to any negative phenotypes that must be bred out. Above all else, breed plants you enjoy. You might not win the Cannabis Cup, but you will have the satisfaction of creating a unique marijuana strain.

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