Can You Tell if a Cannabis Seed is Male or Female?
W hen it comes to growing cannabis, sex is important. Not that kind of sex! We’re talking about the sex of the plant, and whether it is male or female. The reason for this is simple enough: only female seeds produce flower, also known as the buds you might have in your stash as we speak.
- Cannabis Seeds Explained
- What to Look for When Buying Cannabis Seeds
- How to Germinate a Bag Seed
- Understanding the Anatomy of a Cannabis Plant
Cannabis seeds can be male, female or hermaphrodites. Females produce the resin-secreting flower, and males make small sacs of pollen near the base of the leaves. Over the years, cultivators have learned that un-pollinated females (remember, males produce pollen) continue to make resin as they grow, and flowers that have not been pollinated are much more likely to produce high-potency cannabis. This is the basis of all modern medical and recreational cannabis cultivation, so determining the sex of a plant is highly important. But is there a way to know if a seed is female before growing?
Table of Contents:
- Determining if a Cannabis Seed Is Male or Female
- What Are Feminized Cannabis Seeds?
- Methods for Feminizing Cannabis Plants
- Separating Male and Female Cannabis Plants
- How Important is Your Plant’s Sex?
Determining if a Cannabis Seed Is Male or Female
The straightforward answer is that, if what you’ve got is a handful of unmarked seeds, it’s pretty much impossible to tell which ones are male or female. The only true way to tell the plant’s gender is to plant a seed, then wait for it to mature.
After a period of several weeks, the plant will begin to pre-flower, or form a small bud in the crux of a branch. One of the first signs your cannabis plant is female is the appearance of pistillates that are wispy and generally white in color. Male plants will instead produce pollen sacs that look rounded with distinct splits running lengthwise, a bit like a tiny crab claw. These are the structures that growers typically look for to determine a plant’s sex.
If you’re looking for more precise, science-based methods to tell your plant’s gender, there are several labs that can sex your plant right after germination – eliminating the lengthy (usually around 6 weeks) wait to learn its gender. Portland, Oregon start-up Phylos Bioscience is in the business of studying cannabis genetics, and they sell a “plant sex kit” that’s pretty simple to do, even for the folks that aren’t scientifically inclined. Simply press a cotyledon, or embryonic leaf, onto the kit’s filter paper and send it to their lab. They then test the leaf for the “Y” chromosome to determine its gender, just as would happen for a human male.
What Are Feminized Cannabis Seeds?
While it’s basically not possible to determine the sex of a seed from a random bag of seeds, a practice known as feminizing is quite popular. Feminized seeds are selectively bred to produce only female plants.
While the process is very effective, it’s not perfect. There’s a chance that a small fraction of the seeds produced via the feminization method will sprout hermaphrodites, which are still capable of producing pollen.
Despite the potential for ‘hermies,’ knowing your seeds are female from the beginning is probably your best bet.
There are many companies that sell feminized seeds, but buyer beware, do your research to make sure the seller is reputable, especially if purchasing online. Thanks to modern technology, most feminized seeds from reliable brands will be 100% female as advertised – but that doesn’t mean there aren’t people selling low-quality seeds out there.
Methods for Feminizing Cannabis Plants
If you have some experience growing cannabis and would like to bend a crop to your will to ensure that the seeds will be female, there are a few feminizing methods you might try. One such technique is to literally stress out a healthy female plant by interrupting the light cycle during flowering, called Rodelization Feminizing.
In the colloidal silver feminizing method, distilled water is mixed with pure silver and sprayed on female plants. This method works best when the plants are flowering. This results in pollen sacs being formed, which will allow the seeds to produce female plants.
Feminizing via the silver thiosulfate technique involves carefully selecting a nearly mature female plant, then spraying it with a 50/50 mix of sodium thiosulfate and silver nitrate. This triggers a gender change, from female to male. Place this plant back with the others to pollinate other female plants, and female seeds are created.
Separating Male and Female Cannabis Plants
As anyone with seasonal allergies can attest, it only takes a little bit of pollen to have a big impact. The reason that growers are so intent on weeding out male cannabis plants is that a single pollinator can negate an entire potential harvest.
How? The reason is that once pollinated, cannabis plants will cease devoting energy to growing flowers and will tell the existing flowers to stop producing resin, which translates to making less buds and less THC. That energy will be devoted to producing seeds instead. Think of the plant as a battery with a set amount of power. When that supply is spent in one area, it won’t be available for another.
Now consider that a single male plant can spread its pollen to an entire room of females.
If a grow is accidentally pollinated, that means the resources that were spent to bring the plants to that stage — the water, soil, electricity, fertilizers, not to mention the price of the seeds themselves — will have been wasted growing weed that can’t be smoked.
All of those male plants will have to be carefully separated from the grow space and destroyed, or else the growers risk another disastrous accidental pollination. It takes minuscule amounts of pollen to pollinate a plant, so growers must take extensive precautions to eliminate potential contamination. In addition to helping mitigate other contaminants, this is one of the main reasons that many workers will don full-body suits when working in a grow room, ensuring that accidental pollen exposure is kept to a minimum.
How Important is Your Plant’s sex?
How much time you want to spend figuring out the sex of your cannabis plants really depends on how much time and energy you’d like to devote to growing your own marijuana. If you are a medical cannabis patient or caregiver, for example, and need to know what kind of cannabis you are getting every time to keep a reliable supply, buying feminized seeds from a trusted seller is the way to go. It may even be worth it to have your plants tested for sex before they mature. However, if you have some time, consider yourself a green thumb, and want to experiment with your grow, you could simply plant your seeds and see what comes up. Happy growing!
What are your thoughts on feminized seeds? If you’ve used them before, how did it go? Share your experiences in the comments below.
Erin Hiatt is a New York City-based writer who has been covering the cannabis industry for more than six years. Her work – which has appeared in Hemp Connoisseur Magazine, PotGuide, Civilized, Vice, Freedom Leaf, MERRY JANE, Alternet, and CannaInvestor – covers a broad range of topics, including cannabis policy and law, CBD, hemp law and applications, science and technology, beauty, and psychedelics.
Erin’s work and industry insights have been featured on the podcasts The Let’s Go Eat Show, In the Know 420, and she has appeared as a featured panelist on the topic of hemp media. Erin has interviewed top industry experts such as Dr. Carl Hart, Ethan Nadelmann, Amanda Feilding, Mark A.R. Kleiman, Dr. James Fadiman, and culture icons Governor Jesse Ventura, and author Tom Robbins. You can follow her work on LinkedIn, WordPress, @erinhiatt on Twitter, and @erinisred on Instagram.
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…
(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 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 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.