Are genetics the sole determinant of cannabis sex, or do growing conditions play a role too? Learn more in this article. Hydroponic Marijuana Sexing Marijuana sexing simply means determining the gender of your marijuana. While cannabis occasionally may be hermaphroditic (having both pistils and stamens), generally, Regular sexed Cannabis seeds represent a breeding line that expresses an equal balance of male and female chromosomes. Working from seed using regulars is an excellent…
Cannabis Sex: What Determines It?
Both genetics and environment play a role in the determination of the sex of a cannabis plant. Many growers focus on the growing conditions to ensure that hermaphroditism does not take place, but genetics play just as important a role.
Cannabis sativa L. is a dioecious plant – in other words, the male and female sexes are expressed in separate plants. With that being said, some cases of hermaphroditism are known to occur. The most desirable and psychoactive component of the plant is formed in the female flowers. Thus, knowing how to differentiate between male and female plants is integral to any grow operation, whether commercial or at home.
Male cannabis plants have their purpose, too. Even if the buds are not harvested for sale or consumption, male plants are imperative to a breeding program. For this reason, growers and breeders must know the differences between male and female plants and what determines this, especially to avoid hermaphroditism.
Which factors influence the sex of a cannabis plant?
How and why the sex of cannabis plants is determined is a subject frequently discussed by cannabis growers all over the world.
The determination of gender in human beings is simple: the male, who possesses both X and Y chromosomes, either gives or does not give a Y chromosome to the embryo. If it does, the child is born a male. If it does not, the child is born female. However, recent studies have shown that under stressful conditions, the male is more likely to produce spermatozoa containing X chromosomes.
In human embryos, a single X chromosome and a single Y chromosome denote a male (XY). Two X chromosomes denote a female (XX). The combination of genetics from egg and sperm create a diploid cell, containing two chromosomes.
In the case of cannabis, things are a little more complicated. While cannabis has been identified as having diploid cells, there are researchers producing tetraploid plants of cannabis for the purpose of improving its medical qualities. Tetraploid cells contain four chromosomes of either X or Y (XXXX, XXXY, XXYY, XYYY or YYYY). However, it is unlikely that tetraploidy occurs in cannabis in nature.
Generally speaking, in mammals, sex is determined at birth, with no interference on physical sex by developmental conditions. For example, even under stressful circumstances, a female reproductive organ won’t turn into a male reproductive organ. However, this does occur in cannabis. Therefore, the genetic make-up of the seed cannot be the sole factor involved in determining the sex of marijuana plants.
It is for this reason that some cannabis growers place more importance on growing conditions. Under extreme or poor growing conditions, there is a predominance of male plants. This is not so farfetched, as the main objective of a cannabis plant is to procreate.
Essentially, for a male plant to grow under adverse conditions is a defense mechanism of the cannabis plant, as one male can pollinate hundreds of female plants. The effect of growing conditions on both male and female plants will be discussed later in the article.
So as the understanding of cannabis cultivation has it, both nature (genetics) and nurture (growing conditions) influence the sex of the cannabis plant. But how exactly does this work?
Cannabis and Sex – What A High Can Do for You
1. Nature: The role of seed genetics
As much as growing conditions play a vital role in determining the sex of cannabis plants, there is also plenty of genetic information stored in seeds. In the presence of optimum growing conditions, it is the seed genetics which will determine the sex of the plant.
Botanists and researchers of this 2004 study identify fragments of gene sequencing that determine the sex for both male and female plants. They also identified certain gene fragments which may play a role in the development of hermaphrodite plants. In any case, the results of this study show that the genetics of a plant play a role in determining the sex. The commitment to a specific sex takes place as soon as the leaves of the fourth node emerge.
Remember, this is different to determining the sex of a plant as a grower. Cultivators do not need genetic identification material to understand if their plants are male or female. Rather, certain signs in early plant life can be used by a grower to help them determine the sex of their plant.
2. Nurture: Growing conditions and feminisation
The feminisation of cannabis seeds is a perfect example of how cultivation conditions are also intrinsically linked to a plant’s final sex. Feminisation consists of taking a female plant and turning into a hermaphrodite by creating environmental stressors. At this point, certain female flowers will begin to produce pollen, which can then be used to pollinate the same plant. The final product is a feminized seed.
The Evolution of Cannabis Sativa & the Cannabis Ancestor
Which external factors can affect which sex the cannabis plant manifests?
In general, plants that are subjected to stress around 3 weeks into vegetation are more likely to manifest male genetics. If stress takes place later on in vegetation or during flowering, a plant may be forced into hermaphroditism.
When humidity exceeds the optimum amount for cannabis, it is more likely that male plants will develop. In conditions with less relative humidity, it is more likely that female plants will develop.
Interestingly, the moisture of the soil is another environmental condition that can affect the sex of a cannabis plant. In soil that contains too little moisture, it is more likely that a male plant will develop.
The warmer the environment, the more likely it is that a male plant will develop. However, with that being said, it is possible that this stressor is linked with the photoperiod. In warmer climates, there are generally longer days and shorter nights, and the effect of temperature is inextricably linked with photoperiod.
In indoor cultivation programs, the grower may choose the colour of the light spectrum. The more blue light appears in the spectrum, the more likely that female plants will develop.
Finally, photoperiod is an important environmental condition that can affect sex. Shorter light hours per day usually results in more female plants, while longer exposure to light usually results in more male plants.
Ultimately, any grower can force a developed female plant into being a hermaphrodite by adjusting the environment. Changes in photoperiod, increasing the temperature, harvesting too late or over-fertilizing may all result in a female plant turning into a hermaphrodite. With that said, hermaphroditism may also occur as a result of genetics, as some strains are more prone to hermaphroditism than others.
When plants are kept in the correct optimum environment for their genetics, there is generally a small likelihood of hermaphroditism unless the seed is genetically prone. This is why growers must pay close attention to the cultivation environment to avoid hermaphroditism.
Long story short: As almost always, it’s not nature and nurture. A combination of both genetics and environment play a role in the determination of the sex of a cannabis plant.
Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.
Hydroponic Marijuana Sexing
Marijuana sexing simply means determining the gender of your marijuana. While cannabis occasionally may be hermaphroditic (having both pistils and stamens), generally, plants are wholly male or female. After four or five weeks you will start to have a chance at sexing the plants. Although generally considered one of the trickiest parts of growing your own marijuana. Marijuana sexing is quite straightforward and will become easier as you gain more experience. The reason for sexing your plants is so that you can remove male plants before they have a chance to pollinate the females. If this occurs the females will start to develop seeds and this will divert their energy from THC production. Which if course is not cool. Left to their own devices plants will develop pre-flowers after around 4 – 6 weeks. This is the right time to remove the males and commence the flowering stage. Marijuana is a dioecious plant which simply means that the males will produce pollen and the females will produce seeds. Although, as in other forms of life, hermaphrodites do occur. Unless you are a breeder or otherwise growing for seed stock, it is preferential to have all female plants as it is the unfertilized calyx or buds which are the most psychoactive and potent part of the plant, the THC, CBN and CBD. So your seedless buds (sinsemilla) are the most preferred harvest for smoking as no energy or weight has gone into making seeds. Therefore, to use energy, time and space on male plants is wasteful of limited resources; thus they should be identified as early as possible and either segregated (for breeding) or destroyed before they release their pollen. Occasionally marijuana will show pre-flowers (immature indicators of the sex of the plant) while still in the vegetative state, but generally require the shift to the flowering phase (shortening the light regimen to 12/12 – 12 hours of light and 12 hours of total dark).
Flowering is the only true way to sex your plants
Although you may get a clue from their growth patterns before flowering. Male cannabis plants tend to be leggier than female plants with a longer internodal length. Female plants are squatter with more leaves and a bushier aspect. Male pre-flowers should be clearly visible to the eye, although a magnifying glass will make your job easier. Male flowers form at the junctions of the branches and stem and the pollen sacs form little balls. Female pre-flowers will also form at the junction of branches and stem but will normally start to form at the fourth or fifth branches up from the base. They are easily distinguished by the appearance of pairs of tiny white hairs, known as pistils. Some growers force flowering by changing the light cycle before the appearance of pre-flowers. They then watch their plants closely for the appearance of flowers and remove the males. However, others believe that this can stress the plants and is not a proven way of speeding up the process as plants forced in this way may spend longer in the flowering phase, cancelling out the advantage.
A magnifying glass is helpful though not necessary. Look near the top branches right where they fork from the stalk. The male sex organ will look like a small playing card-type club. The female sex organ will display a calyx with two small white hairs protruding from the top. If you are unsure or unable to determining the sex, then simply wait a few more days until the organs are more mature and easier to identify. The males are still way too young to create pollen so there is no danger in waiting.
- Force flowering by putting the plant under 12/12 light cycle. The drawbacks of this are that two separate rooms or grow spaces are required. More importantly the plant gets hormonally confused being switched between vegging to flowering, then back to vegging and finally flowering once again. This method allows you to cull your males early, but most likely will delay your harvest for a few weeks.
- Cover a lower branch with black plastic cut from a garbage bag. Do not use a thin bag that allows light to pass through. This must be put on every 12 hours and removed every 12 hours at the same time. The branch will show its sex long before the rest of the plant while still allowing it to ‘veg’ otherwise normally.
Occasionally a plant will exhibit both sexes. This usually occurs when a female plant is late into flower and remains unpollenated. In a last ditch effort to create seeds, marijuana plants have an emergency back-up plan: they sometimes create a small number of male flowers in an attempt to pollinate themselves. Some growers pinch off the few visible ‘bananas’; others may remove and/or destroy the plant so as not to pollenate a whole crop. Marijuana sexing is not difficult once you familiarize yourself with some basic plant physiology.
Cloning marijuana is a great method to use as all shoots are genetically identical to the parent. Thus if you find a donor parent plant that you like (one with desirable genetic traits) and is large and healthy enough to remove branches for cuttings, you may skip the whole sexing ritual as they are 100% the same sex as the parent.
Feminized marijuana seeds
These are a relatively new phenomenon on the cannabis culture scene, and while looked down upon by some old-timers, purists and large-scale growers, are a great boon to the small grower with limited space and time. It is currently not possible to tell the sex of a cannabis seed by examining it (though many untested myths abound), but the mix of males and females is roughly half and half. The larger the amount of seed purchased and/or planted, the closer the ratio will be to 50%. However, if you purchase a small quantity such as five seeds, it is possible to get all males, all females or any mix in between. Feminized marijuana seeds are not foolproof nor 100% guaranteed, but ratios of 90%+ female are quite common.
A Guide To Regular Cannabis Seeds and How To Sex Plants
Regular sexed Cannabis seeds represent a breeding line that expresses an equal balance of male and female chromosomes. Working from seed using regulars is an excellent way to grow out large selections of either male or female plants. Knowing which plants belong to which sex, how to identify them early on and understanding the life cycle of a Cannabis plant, will give you the advantage when pheno hunting for an upcoming breeding project.
Why Grow Using Regular Seeds?
There are many reasons a grower may choose to work with regular seeds, despite the practical advantages in terms of growing space, waste of nutrients and medium.
For those who have the desire to make your own custom genetic crosses, starting your own breeding project in the comfort of your own home is easily achievable. For this you will need to invest in regular seeds that will allow you to grow either male or female plants. It is a good idea to start with at least 10 seeds to allow for a much wider variation, and greater choice of male to females. Some seedlings may underperform and be discarded early on, however with 10 seedlings, there is a good potential desired ratio. Labeling your pots with numbers and strain names, will make life much easier when sorting through the different plants, especially when taking cuttings before flowering for preservation purposes.
Pre 98 Genetics
There are plenty of old school genetics that have stood the test of time, and due to the marketplace during that era, were never feminized. It was from around early 2000 onwards, when the advantages of feminized seeds were becoming commercially popular. Many cultivars that existed during the last 50 years are often preserved in regular seed form, either as a first generation or as a stable IBL. Back crossing or producing a new generation of cultivar should only be done with regular seeds, especially when in-breeding.
Advanced Phenotype Hunting
When investing the time and money into a large pheno hunt, it is better to work with regular seeds over-feminized seeds. During this process the male and female plants will need to be separated well before flowering. There will be some impracticalites associated with this method such as wasted hydro system space, use of nutrients, growing medium, dedicated space, and maintenance. Working with a large number of plants to select from will allow you to access the best looking plants, based on height, structure, internodal spacing, aroma, leaf pattern, and overall vigor.
There are also commercial advantages when flowers are sold with a dedicated number such as Gelato #33, Gelato #45, KM11, or O.G #18.
Finding A Mother
Working through a bunch of seeds and narrowing down the best female plants to one keeper, will reward you with the ultimate mother plant, and can often soften the blow of paying three figures for a pack of seeds in some cases. If you truly want to find the best of the best, using regular seeds will allow for the most genetic diversity.
When a Cannabis seedling has been left to grow for up to 5 weeks under 18/6, the plant will begin to exhibit very small preflowers. Typically these preflowers reveal themselves once flowering is induced, however it is possible to see which sex you have when knowing what to look for.
Characteristics of Male Preflowers
Male preflowers will look like a small cluster of green, oval-shaped growth. They will be noticeable between the internodal growth and can even look like a female preflower minus the pistil. By this point there is zero need to worry about male pollen sacs and cross pollination, and after several weeks, it will be evident if you have an abundance of tiny male preflowers forming.
Characteristics of Female Preflowers
Unlike the male preflower, the female will produce a tiny white hair known as a pistil. When you see the first white hair, this will indicate the plant is in fact female, and an abundance of pistils will emerge once flowering is induced. Sometimes there can be a very thin and narrow growth, similar to the tip of a blade of grass, that later pushes out a pistil.
Top Tips On Sexing Cannabis Plants
- Make sure you are 100% confident that the plant in question is either male or female, prior to discarding from your garden. Male pollen sacs will not be encouraged to open until weeks 3-4 of 12/12, so take the time to be totally sure of your decision making ability.
- The conversion rate of female to male plants will be usually around 60/40, so the more seeds you plant then the greater chance you have of finding the elite keeper male or female plants.
- Use a magnifying glass or high-powered lens, to get up close and personal with your plants. This will make life much easier considering the flowers can be almost invisible to the naked eye at first.
- Take at least one cutting off each plant if you have the space and time. Make sure that you label and number the clones accordingly to the same numbers from the original plants. Taking clones now will save you from reverting the plants back into a vegetative state once they have been harvested.
3 Advantages of Feminized Seeds
Using regular seeds have their own unique advantages, however it is also good to consider the benefits associated with female seeds.