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

Table of Contents

  • Leaf Sample Testing (Bonus) – Identify sex in 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 Sex (How to Increase Ratio of Female Plants)

Example of Male and Female Cannabis Pre-Flowers

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.

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?

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.

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)!

How To Tell Sex Of Your Cannabis Plants

Sexing cannabis plants is really just finding out whether they are male or female, this can be very important for various reasons, ranging from a breeding project to extensive phenotype hunting. Knowing how and when to tell if your plants are male or female will give you an advantage when growing indoors.

In this article, we explain how to tell the sex of your Cannabis plants, what traits to look for, and what can go wrong.

1. The First Signs of Pre-Flowers

When growing from seed, Cannabis plants will spend the earliest stage of their life cycle focusing on the root, leaf, and stem production.

On the basis that a grower keeps a plant growing under 18 hours of light with high humidity levels of close to 75%, for 5-6 weeks then the plants will begin to show preflowers.

After your plants grow to the 6th or 7th internode, you will be able to identify by eye potential male or female traits.

Cannabis plants that are put into flowering from the seedling stage, will still require 3-4 weeks before the first signs of pre-flowers appear. These are the very first signs of the Cannabis plant’s sex and will either be a tiny male or female pre-flower.

Some cultivars may produce pre-flowers faster than others, however, all plants will reveal themselves around the same time. There is absolutely no need to worry about identifying male plants early on, as they will not be able to produce pollen until a much later time.

2. Male Plant Characteristics

The number one fear any beginner grower has when working with regular sex seedlings is to allow a male to pollinate the entire crop. There is no need to be concerned if your intention is to pheno hunt all the female plants, as removing males before they produce sacs will cause no need for concern.

Male Cannabis plants will produce pre-flowers in the same places as the females. Not only does this make distinguishing between the two early on even more difficult, but it may also take a few weeks before you can completely confirm you have a male plant.

You will notice between the upper internodes, there will be a small cluster of miniature oval-shaped balls. As they mature, you will notice they are attached to a tiny stem and will become bigger and turn green.

• Top Tip: It is best to wait until you can identify the male characteristics, before throwing any plants out of the garden. Do not be overzealous and potentially discard a female plant.

3. Female Plant Characteristics

It is much easier to spot a female preflower, as you are only looking for a thin, hair shaped pistil. When these emerge from between the internodes, they will look like a white eyelash or a tiny blade of grass.

Over time, white hairs will begin to grow amongst the new growth and can be very hard to spot. Double-check what you identify as the female preflower, and wait until you can clearly see a white pistil.

After the first signs of pistils emerge, over the following weeks, the female plants will begin to display an abundance of pistils. This is where plants require higher amounts of Phosphorus and Potassium encouraging flower production and produce buds.

• Top Tip: It is best to use a magnifying glass, or loupe for checking trichomes to double-check. It may take a week or two before you can confidently say you have a female.

4. Using Feminized Seeds or Clones

The only sure way to determine sex before your plants reach maturity is to c lone the plant. T his could be achieved by taking a clone from any plant.

Growing with Cannabis seeds or clones, that are guaranteed to be all-female, has many advantages from the small-scale bedroom grower, to the large commercial ones.

Cut one of the branches then put into a small cup with medium and let to grow for a few days. After the clone’s roots have developed a bit, place it under a 12/12 life cycle.

Soon, the plant will reach maturity and show its sex, because clones share the same DNA as the plant where it was taken from, the clone will show the sex the main plant has.

Note: This tip cannot be used with autoflowers because they start flowering based on age and not photoperiod.

If you are not working on a breeding project and your goal is to grow as many female plants as possible, then using feminized seeds or clones is the most practical route to take.

The Benefits

• This will guarantee that the plants you produce will be 100% female, meaning that prior to flowering, there is no requirement to pull plants out of the grow room. This eliminates any waste of space, nutrients, and growing medium.

• Large scale Sea of Green operations can be set up, without the need to worry about any male plants. This means the crop will not be cross-contaminated with pollen and become seeded and commercial useless.

• Working with clones is an excellent way to grow something that has already been verified. Usually, highly desirable clones can be vouched for by another grower or will have lots of information to research online.

5. In Conclusion

Knowing how to identify male and female Cannabis plants when using regular seeds, is vital to ensuring an all-female crop is maintained.

We recommend you take your time before throwing out any plants and be prepared to allow male plants to mature enough to see their pollen sacs forming.

Sexing cannabis plants is really just finding out whether they are male or female, this can be very important for various reasons, ranging from a breeding proje