Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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by Nebula Haze


Table of Contents

Intro: Use Pre-Flowers or Testing to Find Sex of Young Plants & Seedlings

  • Leaf Sample Testing (Bonus) – Identify gender just 1-3 weeks from germination
  • Male Pre-Flower Pics – Appears 3-4 weeks from germination
  • Female Pre-Flower Pics – Appears 4-6 weeks from germination

Variability of Plant Gender (How to Increase Ratio of Female Plants)

Example of Male and Female Cannabis Pre-Flowers

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)


 

How to Determine Gender 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 gender 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 gender.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

Knowing the plant gender 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 due to the fact that 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”).

​Why Do Only Female Cannabis Plants Make Buds?

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.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

(What is the purpose of “stipules”?)

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 gender 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. Gender 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 gender 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 Gender & Future Cannabinoid Ratios of Very Young Marijuana Seedlings! 

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

But for those of us using our eyes…


 

Male Pre-Flower

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

More Male Pre-Flower Pics

Female Pre-Flowers
(these turn into buds)

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

More Female Pre-Flower Pics

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.

READ
Which Nutrients Should You Be Using?

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 gender it is.

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

Learn more about why it’s hard to determine gender from looking at seeds

 

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

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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 gender 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 cards. Male cannabis plants often (but not always) reveal their gender sooner than female plants.

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

This male plant was only 3 weeks when it made its first preflower. Notice how tiny it is compared to the giant-sized thumb! Often it’s unclear what the gender 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.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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?

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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.

READ
Complete Guide to Cannabis Plant Training

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

A single male pre-flower appears

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

Another example of pollen spilling onto a nearby leaf

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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


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.

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)
pic by GypsySpirit WhiteEagle

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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 gender 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)

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

READ
Under-watering

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

Female cannabis calyxes with pistils, under an LED grow light

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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!

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)


Variability of Cannabis Plant Gender – 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 gender 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 gender 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

Cannabis Pre-Flowers: Find Sex of 3-6 Week Old Plants (with pics!)

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 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 first few weeks
  • Happy Roots – Avoid over (and especially) under watering

Once a cannabis plant is about 3 weeks old, its gender 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 gender, 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 genders of clones will always match each other. This is further evidence to indicate that the environment can affect gender expression in some cases.


 

Jump to…

What’s the Difference Between Male & Female Cannabis Plants?

Male Plants, Bananas & Hermies

Where can I buy feminized seeds?

What do I need to get started growing indoors?

 


 

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