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Sex in the Growroom: A Breeding Affair

Nico Escondido

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When we talk about “sex” in the growroom, a couple of meanings come to mind. For those who have ever started a cannabis plant from a regular seed, the first thought centers upon determining the sex of your young seedling. For the more serious grower who has forayed into the adventurous world of breeding, this phrase will conjure memories of hybridization projects, likely involving lots of pollen, seed shucking and high hopes for finding a new wonder strain.

This latter inclination is perhaps one of the most fascinating aspects of cannabis. However, before we can begin to understand the basics of breeding, we must first understand the basics of cannabis genders.

Male vs. Female

For new cannabis growers, one of the most oft-asked questions is how to determine the sex of a young seedling. To start with, it’s important to remember that cannabis is a dioecious plant, meaning that it will produce either male or female flowers. In rare cases, hermaphrodites do occur—meaning that a single plant will exhibit both genders—but these cases are usually due to harsh environmental conditions and poor plant genetics. Most plants started from regular (i.e., non-feminized) seeds will produce a seedling that is either male or female.

The primary reason that growers want to know as early as possible whether their plants are male or female is so that they can remove the males from the garden before they begin to produce flowers. Male flowers take the form of small, roundish pods, which grow bigger and eventually turn into full-blown pollen sacs. In contrast, female plants produce the gorgeous flowers that have graced the pages of High Times for decades. Should any male plants release their pollen around these lovely females, the buds on the female plants will shut down their resin production and begin forming seeds within their flowers. The result is seeded bud that is also less potent—neither of which is desirable to the cannabis connoisseur.

Determining Gender

Determining the gender of a young plant—or “sexing” the plants, as it is commonly called—is the process of identifying whether a plant will be male or female at the earliest possible time. This can be a tricky, even harrowing, experience for new growers, as a race against the clock begins: Once the male pre-flowers begin to show, there may be less than 10 days before the pollen sacs are fully developed and begin releasing pollen. Identifying males at the onset of development is crucial in producing a garden full of sinsemilla (a Spanish term meaning “without seed”) bud.

To determine the sex of a plant at the onset of maturation, we look for pre-flowers, which generally start to show between weeks four and six of vegetative growth. This timeframe depends largely on how long the seeds took to germinate and take root: Advanced seedlings may exhibit pre-flowers as early as week three or four, while slower-developing plants may take six to eight weeks. For this reason, patience and diligence are critical during this process.

Pre-flowers start to appear on plants at their internode sites. The internode length is the space between two joints or branches on the stem. For our purposes here, the internode site is the place where a branch and stem meet. Depending on the age and height of the plant, pre-flowers first appear between the sixth and twelfth internode lengths a month or so into the vegetative stage. You will see minuscule pre-flower formations begin to develop at these internode sites.

Male plants will begin to flower earlier than females. The first sign of a male plant is the elongation of the internode lengths near the top third of the plant. As the male plant stretches, very small yellow or pale-green growths appear. These take the form of a single tiny shoot, which will develop into a hanging cluster of pods that eventually fill with pollen.

Females, on the other hand, develop flowers at the internode sites a week or two after the males start. These pre-flowers first appear as two stigmas that take the form of a “V.” The stigmas are white and usually hairy or have fuzz running along them. Soon, a tiny green pod forms at the base of the “V”: This pod contains the ovule, which, should the plant become pollinated, will hold a developing seed one day soon. If left unpollinated, these flowers will continue to develop around one other, forming tight clusters that eventually produce the denser flowers we have come to know simply as smokable “buds.”

More Tips on Sexing

Besides watching for pre-flowers, there are some basic (and less complicated) ways that growers can determine plant gender. However, while these methods are easier, they may not be as accurate.

Plant height: Once out of the seedling stage, male plants grow taller and faster than females, thereby making it easier for them to pollinate the surrounding female plants.

Branch stacking: After the initial seedling stage, females exhibit shorter, stockier growth. Their internode lengths will be much shorter than the males’, and their overall shape will be bushier and rounder.

Node swelling: A pronounced swelling at the nodes is usually a sign that the plant is female.

Breeding Basics

Now that we have an understanding of the differences between male and female cannabis plants, it’s time to look at how they breed and, more important, how they can be selectively bred. Pollination between the two sexes in nature occurs just as one might expect: Everything from the birds and the bees to the blowing wind can contribute to ensuring that the male’s pollen makes its way to female flowers.

Once the pollen arrives, it attaches to the stigmas of a female flower and travels down into the ovule, where it will be enveloped. Once it’s been fertilized, the ovule will begin to develop into a seed. A single female plant is capable of producing tens of thousands of such seeds in a single harvest.

In nature, cannabis plants aren’t picky about their mates. But once human growers enter the equation, they can be quite selective about which plants they want to cross. Selective breeding via artificial pollination almost always takes place indoors and is performed by growers who have carefully chosen the male and female plants they want to produce offspring. This selection is based on the desirable traits that the breeder wants manifested in the progeny—everything from color to potency (cannabinoid levels), flavor and aroma (terpene content), maturation time and so on. After the selections are made, it’s time for sex in the growroom.

For most breeders, whether they’re amateurs or master growers, the key is always to determine the sex of their plants early on. Once their sex has been determined, the males are moved to an isolated space where they cannot interact with the females. Each group of plants is allowed to mature, and cuttings are taken to produce clones. Once mature, the flowers of both the male and female plants are harvested and tested, either by smoking, lab tests or visual inspection—or all three. Finally, once the most desirable mates are chosen, the clones are regrown for the breeding process.

This selection and testing process is time-consuming, and sometimes the steps are repeated several times, with several groups of seeds being grown out as the breeder looks for special phenotypes of each strain. But once the breeder finally settles on the male and female plants, the male’s pollen can be collected and applied to the female’s flowers using cotton swabs (Q-tips) or small paintbrushes.

Alternatively, if the breeder is looking to create a lot of seeds or pollinate an entire female plant—or even several females at once—the male can be placed inside the same growroom as the females. Once the male plant is mature and his pollen sacs are full, they will open and unleash small bursts of pollen. With the help of a small oscillating fan, most of the female flowers will receive pollen and begin forming seeds. Placing a saucer or paper plate at the base of the male plant will help catch extraneous pollen that can be stored and used again in future breeding projects or applied to the females manually.

Once pollinated, the females will immediately channel all of their energy into seed production (hence the reason seeded flowers are less potent than sinsemilla buds), and some seeds may become viable as soon as two weeks after pollination. But for higher viability percentages, it’s best to wait a couple more weeks, until the seeds are well matured and have a good size and darker color.

Inbreeding vs. Outbreeding

Growers who wish to become breeders must first answer an important question about their breeding goals: Are you trying to produce seeds of your current favorite strain, or are you looking to create something entirely new?

The former is known as inbreeding, and it requires both a male and a female of the exact same strain in order to make seeds that will closely replicate the traits of the parents. The latter option—the creation of a new genotype, which is much more easily accomplished—is known as outbreeding, and it requires a male and female from any two different strains.

Inbred lines, commonly known as IBLs, are much more difficult to create because in today’s age of clones and feminized seeds, it is increasingly harder to come by a male plant of the same desired strain as your female. Compounding the problem is the fact that even if a grower has both a male and a female of the exact same strain, the probability that the offspring will be identical to their parents is only 50 percent at best. This law of genetic probability is captured by a diagram tool that biologists use called the Punnett Square (see Figure 1), which predicts the outcome of a particular breeding experiment. The Punnett Square helps breeders identify the dominant and recessive traits of gene sets based on the outcomes of their crosses. While it can be a tedious process, this is an excellent means of understanding how the best breeders create our favorite strains.

With outbreeding, there’s never a guarantee that the offspring will be anything special. In fact, the results of outbreeding are usually quite the opposite at first—but then, after several plant cycles, breeders can begin to hone in on the desired characteristics. Of course, one of the best results in outbreeding is finding a completely mutant phenotype—something that is rarely exhibited or possibly nonexistent at the time, but possesses an entirely new and highly desirable quality. Outbreeding helps to reinvigorate the cannabis gene pool and is responsible for all of our favorite flavors, aromas and peak potencies.

Female Seeds

The arrival of feminized seeds into the mainstream cannabis market brought with it an intense debate concerning cannabis genetics. On the one hand, it enabled far more hobbyists and home growers to cultivate their own marijuana—something that has aided greatly in the revolution to legalize cannabis in many countries around the world, including the US. On the other hand, by creating so many feminized seeds—nearly 80 percent of all cannabis seeds currently sold worldwide are feminized—we are putting the cannabis gene pool at great risk.

When breeders create feminized seeds, which are essentially a genetically modified organism (GMO), they’re forcing a genetic occurrence that would otherwise happen less than 1 percent of the time in nature. The seeds are created using chemicals that stress female plants to the point of hermaphroditism, meaning the female plant creates both male and female flowers.

Because female plants do not carry the Y chromosome that males do, the pollen created by a hermaphroditic female only has X chromosomes, making the seeds they produce wholly female. The problem here is that the Y chromosome is effectively being bred out. Should this trend continue, the only way to produce certain strains will be by cloning, as the Y chromosome dies off and the male plant is eventually lost. Thus, many cannabis varieties are now at higher risk for extinction, with many strains already lost. So remember: It’s always a wise idea to purchase a small pack of regular male and female seeds along with your feminized ones, since you never know what the future may hold for your favorite smoke!

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