How To Sex Marijuana Seeds

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Are genetics the sole determinant of cannabis sex, or do growing conditions play a role too? Learn more in this article. When growing regular cannabis seeds the chances of them being male or female is 50/50. Find out how to tell the sex of you cannabis plant and ways to prevent any cross pollination happening. If you are looking to get the most female cannabis plants from your regular cannabis seeds, this article is for you.

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?

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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.

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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.

How to sex marijuana plants

Regular cannabis seeds will generally develop into both male and female plants. If you’re unlucky, you may end up with the odd hermaphrodite plant. You need to remove both males and hermies as quickly as possible. Males don’t carry bud and you don’t want them fertilizing the females which do. Hermies do carry bud, but it’s very low quality. They also carry pollen and so can fertilise productive females. Basically, they’re more hassle than they’re worth. The best time to sex marijuana plants is during pre-flower. This is when they first become identifiable as male or female.

Beginner tip

If you are new to sexing marijuana plants, you probably want to start with a maximum of five seeds. Stick to the one strain, so you can easily compare your plants. You also want to leave plenty of space in your growing room so you can physically move plants. This will allow you to “sex in stages”. In other words, if you’re sure a plant is male you can just remove it. If you’re not sure, then you can separate your plants into “females” and “not sure”. Keep them far enough apart that there is no chance of pollen from the “not sures” reaching the females. Then you can work on definitely sexing the “not sures”.

Bonus tip

Statistics can play tricks on people. In principle, regular seeds have a 50/50 chance of being male or female. If you only sow one seed, then it can only be one sex or the other (unless it hermies). If you sow more than one seed then you may or may not get a mix of genders. The more seeds you sow, the more likely it is that you will end up with a mix of genders. It is, however, not guaranteed. You could still end up with all male plants or all female plants. Remember this when you are sexing your marijuana plants. Basically, go by what you see rather than what the statistics suggest you ought to have.

How to sex marijuana plants

Frankly, the easiest way to sex marijuana plants is to use feminized seeds. If, however, you want to do it the “old-school” way, here’s what you need to know.

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Step 1 – Go online

Look for videos showing the difference between a male cannabis plant and a female cannabis plant. If at all possible, look for videos which relate to the strain you’ve chosen. If you can’t find any, look for a comparable strain. In other words, if you’re growing a strain which is 80% Indica dominant, look for someone else growing a strain which is 80% Indica dominant. Then go and look for close-up images of the key parts. Yes, it will be different when you do it yourself. In fact the first time, you may find it a bit of a challenge. Looking at online resources, however, can definitely be a big help.

Step 2 – Stand back and look at your plants from a (bit of a) distance

Before you get caught up in details, take a look at the bigger picture. Male plants tend to grow quicker than females. They also tend to be slimmer and have less foliage. This is, of course, all relative. A male Indica is never going to be as leggy as a female Sativa. A female Sativa is never going to be as bushy as a male Indica. That’s why you want to stick to one strain at first. Then you can make like-for-like comparisons.

Step 3 – Look for pollen sacks

Pollen sacks look, quite literally, like tiny balls. They can be seen with just the naked eye. Having said that, a magnifying device can make the task a whole lot easier. If you see a pollen sack, then a plant is definitely male. If you don’t it may be female. Alternatively, it may still be in the process of development.

Step 4 – Look for pistils

In the pre-flowering stage, pistils are tiny white hairs. They are virtually impossible to spot without a magnifying device. Even with a magnifying device, it can be a challenge to see them at first. Later, as flowering continues, the pistils will become both very colourful and very obvious.

Step 5 – Clone the “not sures”

Take a cutting of the “not sures”. Let it grow for a few days. Then force flowering. The sex of the clone will also be the sex of the host. This trick is 100% accurate – as long as you keep accurate records of what cutting came from what host.

What is a hermaphrodite cannabis plant?

Hermaphrodite plants develop both male and female sexual parts. Hermaphrodite weed is lower in both quantity and quality than regular bud. Sometimes it’s still usable. Sometimes it’s only fit for the (composting) bin.

There are some strains which are frankly notorious for hermying. Reputable seed banks will mention this in their descriptions. You can also double-check with independent strain reviews. These strains are best left to the most experienced growers.

In general, most strains will only hermie if they are exposed to excessive stress. The big five causes of hermying are: ventilation, lighting, temperature, hygiene and handling.

Out of these, ventilation is usually the biggest issue. The reason for this is that it causes so many other problems. For example, poor ventilation means that your plants are too close together. This makes it hard for them to capture sufficient light and easier for them to overheat. It makes it harder for the grower to keep the growing room clean and easier for any problems to spread from one plant to another. Last but by no means least, it makes it harder for the grower to handle the plants appropriately and so easier for them to be damaged.

In short, if you choose a robust strain and remember your marijuana basics, then you should be able to avoid hermies. The less experience you have, the more important it is to choose a strain with solid genetics. Again, reputable seed banks will generally highlight strains which are particularly suitable for beginners. You can also check online for independent strain reviews.

How to Get More Female Plants From Regular Seeds

Statistically, cannabis produces more male plants than females. Using these techniques can increase the number of female plants grown from regular seeds. Make the most of your time, space, and precious dollars by boosting the number of females every grow.

Unless you are planning on doing some breeding of your own and you’re looking for a perfect male, female cannabis plants are what growing marijuana is all about. However, unless you purchase feminized seeds from a reputable source, females aren’t always guaranteed. In fact, statistically, regular cannabis seeds will produce 75% or more males per crop.

It is impossible to tell if seeds are female or male, and very difficult to tell if a young plant is male or female prior to the plant differentiating. Males do have some differing growth characteristics, but it is not always easy to recognize boys from girls in the vegetation phase.

There are techniques and tricks of the trade that can be used for increasing the likelihood of getting more females from regular seeds. The key words here are a “stable growing environment.” Stress tends to produce more males, and undue stress during flowering can turn plants intersex.

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STABILITY IN THE ENVIRONMENT

Stability of the growing environment is essential to increase the female to male ratio. From the moment the seeds are germinated, a growing environment with as few fluctuations as possible is ideal. Stress is the enemy when trying to get females

This is true of all the essential requirements for plant growth. Maintain stable temperatures and humidity. Make sure the photoperiod begins and finishes at the same time every day. Be sure there is no light pollution interrupting plants during the night cycle. Be sure the nutrient mixes are exact every watering. Spikes up or down in nutrient mixes can cause stress, increasing the chance of males.

GIVE SEEDLINGS LESS HOURS OF LIGHT

In the rush to get buds in the jar sooner, it is always tempting to expose plants to 24hrs of light during the vegetation cycle. The plants may grow larger sooner, but this increases the risks of males developing.

Young plants exposed to an 18-6 day-night photoperiod increases the chance of females. The chance increases further when the day length is reduced to 16 hours. To maximize the possibility, reduce the day period to 14.5 hours of light.

Shorter day length does slow growth during vegetation, but the likelihood of females increases to 70–100%. With expensive primo seeds, it is better to allow an extra week of vegetation to get the best value. Some patience during vegetation is preferred to throwing half the crop away later on.

The other downside of 24hr light exposure during vegetation is poor root development and interrupted gas exchange in the rhizosphere. Root development occurs predominantly at night, and necessary oxygen exchange occurs more efficiently at this time too. Healthy roots mean healthy plants.

USE COOL, BLUE LIGHT

Light that is in the blue spectrum during vegetation promotes female development. Fluorescent lights should be white or blue spectrum for infant plants. Refrain from using the purple/red-tinted fluorescents, which are better for flowering.

Metal halide lamps are ideal for the vegetation phase of cannabis. They are blue biased in their spectrum and imitate summer light effectively, which is the natural vegetation period of cannabis. When the 12-12 switch is made to promote flowering, switch to a high pressure sodium light. These a red biased in their spectrum and imitate the red-shifted light of autumn.

INCREASE NITROGEN

Cannabis plants consume lots of nitrogen during the vegetation phase. Increasing nitrogen (N) slightly and reducing potassium (K) can increase the likelihood of females. A potassium-rich nutrient blend will boost the chances of males during the early development phase.

HIGHER HUMIDITY AND MOISTURE IN AIR AND SOIL

High and stable humidity levels from germination right on through to vegetation increases female development. Similarly, consistent and stable watering routines maintain ideal moisture in the grow medium. Stable moisture exposure in the air and medium promotes females.

Young plants: When plants are young, make sure they maintain a high humidity of at least 70–80% RH. This is easily done with a humidity dome during the infant stage. Make sure the growing medium does not dry out too much. There is a fine line between maintaining a healthy wet-dry cycle and over drying. The stress of a too-dry medium will encourage male development.

Pubescent plants: Maintain humidity at 70% RH. Use a hygrometer religiously to ensure ideal moisture content of the growing medium. Maintaining correct humidity is made easier with a humidifier/dehumidifier unit always at work in the grow space. Continue to monitor the moisture content of the grow medium. Overwatering and over drying are stress vectors that can encourage males.

Flowering: Decrease humidity slowly to 40–50% during the flowering phase. Refrain from dropping to this level in one go. Gradual humidity reduction will prevent stress. Too high humidity can cause numerous problems for cannabis flowers. By now, the sex of the plant has been established from the specialized treatment during the vegetation phase.

DON’T STRESS

Following these easy-to-maintain tips can maximize female plant development. Stress of any kind is the enemy of marijuana. It is thought that male development increases the likelihood of pollination during times of stress. A single, well-pollinated female can produce hundreds of seeds, perpetuating the species into the next season.

Indoors, the grower has complete control over the growing environment. This means that any stresses can be minimized with vigilant plant care. Well-maintained young plants increase the likelihood of female plants, which means more buds in the jar at the end of the day.

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