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How are new weed strains created?

Every year, dozens of new cannabis strains are created, each one combining the flavors, aromas, and effects of two or more strains into a new one. Weed tastes and trends change all the time, and cannabis breeders continually create new strains to feed the interests of cannabis consumers. 

Weed is arguably one of the most cultivated plants (we’ve been growing it for at least 5,000 years), and growers can control the breeding and growing processes to select and refine the plant to suit various wants and needs. 

To explain how new weed strains are created, we need to start with plant sex.

Weed breeding 101

The cannabis plant can be either female or male—this trait is called being dioecious and is rare in the plant world. Only female weed plants produce the buds that we all know and love. Whenever you see a field of cannabis plants covered with buds, those are all females. 

Female weed plants also grow seeds, while male plants grow pollen sacs. When males grow to maturity, their pollen sacs open up and release pollen into the air, which can fall onto a nearby female plant and pollinate it. 

male vs female cannabis plants
(Josh Titus/Leafly)

When a pollinated female grows to maturity, it grows seeds with the buds, which carry the genetics of both the female and the pollinating male. When those seeds grow into new plants, they will be a new strain, combining traits of both the male and female.

Out in the wild, cannabis plants breed naturally. A male weed plant may happen to grow near a female plant, and when it releases pollen, the wind will carry the pollen to a female. When a female plant matures and then dies, its seeds will fall to the ground and grow as plants of the new strain the following year. 

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Cannabis Breeding: How Are New Strains Created?

How to create a hybrid weed strain

Breeding can be done artificially and intentionally in a commercial or homegrowing setting. To start, cannabis breeders will select two strains to combine, based on traits such as taste, aroma, potency, effects, yield, ease of growing, and other factors. They’ll pick a female of one strain and a male of another. 

A weed breeder will usually put a male and multiple female plants together in a closed room, called a breeding chamber, to contain the pollen and ensure a successful pollination. Pollination can also happen outdoors by keeping the plants close together, as long as there aren’t multiple strains releasing pollen.

Once a female plant is pollinated and grows to maturity, its seeds will be collected and then those seeds will be grown into plants. These new plants will contain the genes of both the female and male plants and are referred to as a cross (from crossbreeding) or a hybrid of the parent plants.

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Marijuana plant anatomy and life cycles

What is a phenotype?

Simplistically, the new seeds on the female plant are called phenotypes—they’re like the children of the two parent plants, and are like siblings to one another. One pollinated female plant can produce dozens of seeds, or phenotypes. 

Two things influence the structural formation of a cannabis plant: genetics and environment. The plant’s genetic makeup—also called its genotype—acts as a blueprint for growth. It allows for a spectrum of physical possibilities. But genes can switch their expression on and off in response to environmental cues. 

The interplay between the plant’s genotype, or blueprint, and its environment affect its phenotype, which is the physical expression of its genetic code. Observable traits in cannabis plants such as color, shape, smell, and resin production, are shaped by the environment.

Here’s a comparative example with dogs to illustrate phenotypes. 

what is a cannabis phenotype
(Josh Titus/Leafly)

If a Golden Retriever and a Poodle mate and have a litter of puppies, they will be Golden Doodle puppies, which will have traits from both the mother and father. Some of the puppies will look more like a Poodle (maybe they’ll have more curly hair and be tall and lanky), some more like a Golden Retriever (maybe shaggier hair, and a little shorter), and some will have a mix of traits from both parents.

The same is true when crossbreeding weed strains. For example, crossing Lemon Skunk and Super Silver Haze will give you seeds of Super Lemon Haze. All of the resulting Super Lemon Haze seeds will be different when grown into plants: Some will be stinky, tall, and lanky like Lemon Skunk, some will be shorter and packed with more trichomes like Super Silver Haze, and some will have a mix of traits from both parent strains.

Just as a litter of Golden Doodles will yield puppies that display the different traits of their two parents, cannabis seeds or phenotypes will express the different traits of their parent strains. These traits can include plant size and structure (tall, short, bushy, thin), color (purple, orange, light green, dark green), smell (fruity, skunky, sweet, gassy), effects (energetic, sedating, cerebral, giggly), and more. 

All traits will be derived from the parent strains, and each phenotype will be unique in the combination of traits it inherits from the parents.

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Leafly’s guide to growing marijuana

What is pheno-hunting?

When creating a new weed strain, breeders will often pollinate multiple females, resulting in dozens, if not hundreds, of different seeds or phenotypes. So which phenotype ends up on the dispensary shelf that you buy?

A cannabis breeder’s job now is to grow the seeds of the new strain into plants and select the best one to take to market—this is called pheno-hunting. The breeder is looking for the best version, or best expression, of the new strain.

Some of the phenotypes might smell great but not look great; some may taste and look great but not be very potent; some may be susceptible to bugs or not yield very much; and so on. The breeder wants to find the particular phenotype that combines all of the best traits of the new strain.

what is phenohunting
(Josh Titus/Leafly)

Pheno-hunting often takes a few generations to pick the best version of a strain. For example, a breeder might start by growing ten seeds into plants and pick the best five; then those five are grown again and whittled down to three; and then those are grown and whittled down to the final phenotype. Each generation of growing can take months, so pheno-hunting and breeding a new strain in general usually takes several months—or even years.

Once a breeder has selected the phenotype with the best traits, they will mass produce it, and that version of the new strain will go to market and ends up on the dispensary shelf.

Bringing other phenotypes to market

Sometimes a strain becomes so popular that breeders will sell a “spin-off” version to capitalize on that strain’s popularity, and also just to bring a different version of the strain to market.

This explains why you might find two versions of a strain, usually one with a number after it, such as Gelato and Gelato #33, Bruce Banner and Bruce Banner #3, and Northern Lights and Northern Lights #5. The numbered strain is a different phenotype.

For example, originally, Gelato went to market and became popular, and then a grower liked another phenotype of Gelato, in this case #33, and later mass produced that version and sent it to market as well. (When pheno-hunting, breeders typically number each phenotype, and in this case, the 33rd version of Gelato also happened to be a winner.) 

These two versions are different flavors of Gelato, if you will. They have the same parent strains and are similar, but they are also unique in the combination of traits they inherited from their parent strains.

Pat Goggins's Bio Image
Pat Goggins

Pat Goggins is a senior editor who handles Leafly's informational content and specializes in cannabis cultivation after working for a commercial grower in Oregon. When not fixing typos, you’ll probably find him on a boat or in the mountains.

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