Sexing Weed Seeds

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Save up to 8 weeks and reduce operational costs by up to 20% with the LeafWorks Cannabis & Hemp DNA Sex Test. Identify male cannabis & hemp plants as early as 7 days post germination. The LeafWorks Cannabis & Hemp DNA Sex Test is 99% accurate. 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… Learn how to find tiny pre-flowers at the base of each leaf to determine the sex of your plant in the vegetative stage (at only 3-6 weeks from germination)!

LeafWorks Cannabis & Hemp DNA Sex Test

Want to identify male cannabis & hemp plants early in the growing cycle?

Save up to 8 weeks and reduce operational costs by up to 20% with the LeafWorks Cannabis & Hemp DNA Sex Test. You can identify male cannabis & hemp plants as early as 7 days post germination.

The LeafWorks Cannabis & Hemp DNA Sex Test is 99% accurate and because we use more biomarkers than the competition, we greatly reduce false positive test results allowing you to confidently remove male plants quickly.

  • Turnkey collection and submission kit is provided for every order
  • Simply mail your cannabis or hemp plant samples using the collection cards provided
  • Up to 4 plants collected per card
  • National and international orders accepted
  • Tests available for licensing
  • Order up to 25 cards: $60 per card; only $15.00 per plant
  • Order 25 to 250 cards: $50 per card; only $12.50 per plant
  • Order over 250 cards: $40 per card; only $10.00 per plant

3-7 business days after the lab receives your samples, depending on volume of cards to be processed.
LeafWorks only accepts samples through the LeafWorks DNA submission kit. We will not test or receive Schedule I tissue.

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.

Breeding Projects

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.

Identifying Preflowers

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.

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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.

Cannabis Pre-Flowers: Identify Sex of a Plant as Early as 3 Weeks Old (with pics!)

The female plants will soon produce pistils. Wispy white hairs are a sure sign that you’re looking at female pre-flowers.

How to Determine the Sex of a Young Cannabis Plant

What are cannabis “pre-flowers?” They are little versions of adult flowers that appear on your marijuana plants relatively early in the vegetative stage.

When I first started growing weed, I learned (incorrectly) that there is no way to determine a cannabis plant’s sex until the flowering stage. But I’ve since learned that pre-flowers can reveal the plant’s sex while it’s still in the vegetative stage! Cannabis plants grow pre-flowers as young as 3-4 weeks from germination for male plants, and 4-6 weeks from germination for female plants.

Cannabis Pre-Flowers Are Small Versions of Adult Flowers. These reveal a plant’s sex.

Knowing the plant’s sex is helpful because most hobbyist cannabis growers would like to identify and remove male plants from the grow room early in the growing process. This is because only female plants make potent buds/flowers, while male cannabis plants make non-potent pollen sacs where female plants would grow buds. Additionally, female buds need to avoid pollen from male plants in order to make the highest quality cannabis (sinsemilla or “no seeds”).

Cannabis pre-flowers appear at the base of leaves when male plants are about 3-4 weeks old, and female plants are 4-6 weeks old.

Even if you’re not 100% sure about every plant from looking at the pre-flowers, it’s nice to know which plants you need to watch closely and which are definitely female. However, if precision is very important…

Chemical Leaf Tests Can Determine Sex & Potency for plants as young as 1-3 weeks

Chemical leaf testing is getting less expensive every day and can be used on cannabis seedlings with just a few sets of leaves to test for sex and future potency.

These tests only require a tiny amount of plant tissue (for example a small punch-out from a leaf, or a single cotyledon leaf), so it won’t hurt or slow down your seedlings to take a test sample!

In general, the tests are available for seedlings as young as 1-3 weeks. Sex testing uses a real-time polymerase chain reaction (qPCR) test, and potency tests use Gas Chromatography with a Flame Ionization Detector (GC/FID) or High-Pressure Liquid Chromatography with a Diode Array Detector (HPLC) for testing.

Although testing can be done as early as week 1 from germination, waiting until week 3 to conduct testing on seedlings can increase accuracy, and some companies won’t conduct testing until week 3.

There are many reasons growers would like to know plant sex as early as possible, as well as be able to estimate the overall THC/CBD ratios of future buds!

Did You Know? There are Chemical Leaf Tests that Can Definitively Determine Both Plant Sex & Future Cannabinoid Ratios of Very Young Marijuana Seedlings!

But for those of us using our eyes…

Male Pre-Flower

Female Pre-Flowers
(these turn into buds)

This female pre-flower hasn’t released a wispy white pistil quite yet

When starting with “feminized” seeds (which you can usually only get from a breeder), all your seeds should end up being female, so determining male from female isn’t very important. Learn more about buying seeds (including feminized seeds) from breeders online.

But for growers starting with “regular” (non-feminized) seeds, about half of the plants can turn out to be male. And unfortunately, there’s no way to look at a seed and be able to tell what sex it is.

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Unfortunately, you can’t tell a cannabis plant’s sex for sure by looking at the seeds

How to Figure out Sex of a Cannabis Plant by Examining Pre-flowers

Vegetating plants usually reveal their sex when they’re just 3-6 weeks old from seed, but you have to know where to look.

What you’re looking for is “pre-flowers.” These are tiny versions of adult sex parts, and when you see them you can tell what sex the plant is going to be. They usually show up in the upper parts of the plant, closer to the lights, but sometimes you’ll search the whole plant and only find a pre-flower on a random branch lower down on the plant.

Vegetating cannabis plants reveal their sex with “pre-flowers” that usually appear 3-6 weeks from when the plant first germinated.

Although these are the general shapes of male and female pre-flowers, if you continue looking through the pictures below, you’ll see there’s quite a bit of variation on what pre-flowers look like from strain to strain.

Most male plants have grown a pre-flower by week 3-4 from seed, while female plants don’t show until week 4-6. Basically, all vegetative plants will have revealed their sex by about the 6th week from seed.

So, without further ado, here are pictures showing what you’re looking for when it comes to pre-flowers. Remember, pre-flowers are found at the V where stems meet a main stalk. But pre-flowers don’t usually show up all over the plant. Make sure to look around in different places, especially near the top of the plant and closer to the lights

Note: Pre-flowers show up most often near the top of the plant and closer to the lights but could be anywhere on the plant. There may be just one on the whole plant so you may have to search all over!

Male Pre-Flowers

Male pre-flowers tend to have a “spade” shape, like the spades from a deck of playing cards. Male cannabis plants often (but not always) reveal their sex sooner than female plants.

Male pre-flowers tend to be shaped somewhat like a spade

This male plant was only 3 weeks when it made its first pre-flower. Notice how tiny it is compared to the giant-sized thumb! Often it’s unclear what the sex is when a pre-flower is this small (unless you’ve got a lot of experience) so if you’re not sure, it’s a good idea to wait and see how it develops, just in case.

Just to give you an idea how small these can be when they show up…

This is the exact same picture as above, but with the pre-flower made bigger so you can see it. Pretty tiny, isn’t it?

Male pre-flowers are basically immature pollen sacs. When the plant starts flowering, they will grow and turn into bunches that almost look like grapes.

I’ve also noticed that sometimes (though not always!) the stipules on male plants seem more “leafy” and less “pointy” than stipules on female plants (the stipules are the green hair-like growths near where pre-flowers show up). However, this is just a generality, and should be used together with other factors to determine if a plant is male! There are definitely male plants with pointy stipules and vice versa, but it’s sort of a general difference.

This particular pre-flower is really tough to determine. However, in the end, it was a male plant. The little “stem” is one clue it may be male

Just like the above male plant, sometimes you get almost what looks like two tiny little leaves that the pre-flower pollen sac “unfurls” from. In the above picture the pollen sac is still mostly hidden, while in this next picture, the tiny growths have opened up to fully reveal the pollen sac. This can be confusing because these extra growths don’t appear on all plants, and are not a pre-flower or a stipule.

Here’s another male pollen sac pre-flower that’s on a little “stem”

A single male pre-flower appears

Once you see multiple pollen sacs and no white pistils, you can be confident it’s a male plant

Although this plant ended up being male, the stipules are long, pointy and crossed as you’d normally see with a female plant. That’s why you need to confirm sex with the pre-flowers and not just look at other factors on the plant!

Sometimes the pollen sacs look a little unusual when they first start growing in, but you know it’s male when you see several pre-flowers without any pistils stacked on top of each other like bunches of grapes

If you click the following picture and zoom in close, you can see pollen sacs scattered among the leaves

This is what male pollen sacs look like when the plant actually starts flowering

This male cannabis plant has gotten further along in the flowering stage

This is what a male plant looks like at maturity when it’s starting to spill its pollen

Another example of pollen spilling onto a nearby leaf

For those who’ve never seen a male cannabis plant in its full glory

Ok, now that you know what male pre-flowers look like, what do female pre-flowers look like?

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Female Pre-Flowers

Female pre-flowers tend to be longer and narrower than male pre-flowers, sometimes with a fat bottom. They also usually (but not always) have 1-2 white hairs (pistils) sticking out from the top. Sometimes it takes a few extra days for the pistils to appear.

Wispy white pistils are a sure sign that you’re looking at female pre-flowers

This pre-flower doesn’t have a pistil sticking out at first, but the shape helps tell you it’s a female plant. If you’re not sure about sex after spotting a pre-flower, it’s a good idea to wait and see for a little while, just to see if a white hair appears (which means it’s definitely a girl)

Another example of female cannabis pre-flowers that haven’t revealed their pistil yet

Here’s a picture that shows a pistil right as it’s emerging from the calyx!

If the pre-flower is very pointy and thin like this one on the right, it is often a female pre-flower

Some of the time the stipules (green hair-like growths near where pre-flowers show up) will cross each other on female plants. This certainly doesn’t always happen, as you can see from the pics of female pre-flowers on this page, but while girls can go either way, male plants rarely have stipules that cross each other. So although crossed stipules cannot be used definitively as a way to identify female plants, it can be a small clue to help guide you when you’re not sure. For example, the following female pre-flower doesn’t have a pistil, but the long thin shape combined with the crossed stipules help indicate that this plant is a girl. Whenever in doubt, wait a week and look again!

This female plant has a long, thin calyx and crossed stipules, which are typical female plant features

In this pic, you can see white pistils emerging from the calyxes. Female pistils are white and wispy, never green.

Here’s another female pre-flower that doesn’t have a white hair yet, but you can tell it’s female because it’s long and narrow, instead of spade-shaped

One last female pre-flower without a pistil yet. The long narrow shape is the only thing that gives the sex away until pistils begin to emerge

Super close-up picture of a female cannabis pre-flower

Female cannabis calyxes with pistils, under an LED grow light

Did you know that pre-flowers/calyxes/flowers are actually what holds seeds if your plant gets pollinated? Once pollen touches the white pistils, the pollen gets delivered to the inside and a seed starts forming!

Variability of Cannabis Plant Sex – How to Increase Ratio of Female Plants with Regular Seeds

In fact, to this day scientists are still not sure exactly what causes certain plants to be one sex or another after sprouting. We’ve identified several factors that predict the overall likelihood of male/female plants (for example feminized seeds always produce female plants no matter what), but sex seems to be somewhat fluid in cannabis plants when they’re first germinated.

Certain conditions such as excessive heat, stress, unusual light periods and nutrient problems can cause a greater percentage of plants to produce male flowers.

You may be able to increase the percentage of female plants with regular seeds during the first few weeks of life

On the flip side, the following factors may possibly increase the ratio of female plants with regular seeds (learn more):

  • Healthy Mom – Only grow seeds from a vigorous, healthy mother plant who never showed any signs of herming or male pollen sacs (seeds are more likely to grow pollen sacs if the mom plant had a tough start in life, or hermed during the flowering stage)
  • Cool Temperatures – Give seedlings slightly cool temperatures (65-75°F day and night) and avoid excessive heat
  • High Humidity (50-70% RH)
  • Short but not too short days. Keep consistent day and night periods with no light interruptions at night, and days should be 14-18 hours long (between 14/10 and 18/6) for the first few weeks
  • Blue light. Always start seeds under a vegetative grow light (something with plenty of blue like a Metal Halide or a 6500k CFL/T5/fluorescent)
  • Avoid Deficiencies – Make sure to provide plenty of Nitrogen and don’t let seedlings become nutrient-starved or run into other types of deficiencies
  • Prevent Stress, especially heat or light stress during the first few weeks
  • Happy Roots – Avoid over (and especially) under watering

Once a cannabis plant is about 3 weeks old, its sex is pretty much completely set and can be determined either by visual inspection or by chemical leaf test.

Unfortunately, due to the fact that different environmental conditions during the first part of life can alter the sex, you can’t look at seeds and definitively know one way or the other whether the plant will end up being female because even the plant doesn’t necessarily “know”.

For example, say you take a clone of a seedling before it’s 3 weeks old. It’s possible that one clone will be male, and the other clone will be female. However, if you take a clone after week 3, the sexes of clones will always match each other. This is further evidence to indicate that the environment can affect sex expression in some cases.

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