3 Week Old Weed Plant From Seed

Learn how marijuana seedlings develop by checking out the pictures of marijuana seedling growth day by day, With identification tips included Cannabis has a number of different stages. The vegetative stage is when cannabis grows leaves and branches to be ready to support and develop the flowers. Like 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)!

Marijuana Seedlings: Their Anatomy, Growth, and Identification

Your day-by-day and week-by week guide to marijuana seedling plants‘ progress from emergence to vegetative stage

In this post, we’ll talk about the normal growth of marijuana seedlings. It will give beginner growers a pretty good idea of what to expect day by day and help you keep your cool and not react with panic whenever you suspect trouble.

We understand that taking care of marijuana seedlings can be a nerve-racking experience. But it shouldn’t be. Just look at the pictures in this post and compare them with your little plants to see if they are doing okay. And if in doubt, consult our guide to seedling problems and how to solve them.

Table of Contents

Marijuana Seedlings from Day 1 and Onwards

So you’ve germinated your seeds between wet paper towels or using some other method and placed the sprout into a grow medium, like soil, or soil mix, or coco, or rockwool. We recommend covering the sprout by the medium completely, so that its tap root has something to push off from when it’s trying to dig deeper. And when the tap root has established itself in the medium, it pushes the seedling out of the medium and its ‘helmet head’ comes up.

If the medium is moist enough and coarse enough, the shell can peel off on its own. Otherwise, the seedling can be stuck in the shell and needs your help (see the link above to remedy this and any other problem). Below the shell, there is a thin film covering the cotyledons. Sometimes, it sticks and doesn’t let the cotyledons open, even after you have successfully removed the shell.

This is day 1 for three OG Kush Auto seedlings. Only one of them has cast off its shell on its own.

We have removed the shells from the seedlings on the right and in the center. The one in the center still retains the film though.

Sometimes, you will see the weed seedlings sprouting yellow. Don’t worry: it’s perfectly normal. The green color in plants is due to chlorophyll, a natural chemical that plants produce in the presence of light. And this process needs time. Give your yellow sprout a couple of hours under light, and it will start to turn green.

The First True Leaves

When the seedling sprouted, the pair of cotyledons will be ‘glued’ together – the way they used to be inside the seed, but soon they will move apart, and you will see the first tiny pair of true leaves tucked between them. Of course they will be whitish or yellow, too, at first.

On day 1, the cotyledons will be most probably pointing down, but on day 2 they will definitely straighten themselves (and so will the stem), and the first leaves with serrated edges will start to turn green and grow imperceptibly. These first leaves will have only one ‘finger’ each. The second pair – three fingers, the third – probably five.

Most of the Growth is in the Root Zone

The growth in the first week may seem painfully slow to you, but don’t you worry: the plants will pick up pace eventually, and right now a lot of progress is happening underground where the root system develops. The main root, called tap root, tries to reach as deep as it can.

That’s why it’s recommended to use deep pots or tall party cups for cannabis seedlings. But secondary roots also actively grow at this stage which will be evident to you if you use rockwool or jiffy pellets: the root tips will grow through their sides.

Control the Height of Your Marijuana Seedlings

Marijuana seedling height is controlled by the amount of light it receives. If everything is just right, the seedling is sturdy and not too tall: probably 2-3-4 inches the first several days, and hardly much taller when it is 1 week old or even 2 weeks old.

The seedling’s main business at this time is root development and the growth of leaves, not the overall height. If you see that each successive pair of leaves eventually grows bigger than the previous one, your young plants develop beautifully. At day 10, the span of the second pair should be the same as the span of the first one.

When Does the ‘Veg’ Begin?

It’s hard to point to the exact moment in time when a young plant stops being a seedling and begins its vegetative stage. You’ll see it happen when your cannabis starts to get noticeably bigger overnight. It may just grow higher, or rapidly develop side branches, or its leaves will get very large very fast. When you witness this sudden spurt in growth, congratulations: the vulnerable seedling stage is over and the plant has started vegging.

On day 1, one out of three OG Kush Auto seedlings has yet to ‘unglue’ its cotyledons.

This is Day 1 for Cream Caramel that managed to cast off the shell while emerging from the soil. It’s still yellow because it hasn’t yet been exposed to light.

Cream Caramel seedling at day 2. The cotyledons and the first pair of true leaves are already green. The stem is brownish-purple, but it’s perfectly normal.

OG Kush Auto at day 3. The seedling is in the process of straightening up.

This Six Shooter seedling is at day 4, and you can already see the second pair of true leaves.

OG Kush Auto at day 6. A bit stretchy and bent as a result, but oherwise healthy.

OG Kush Auto at day 8. Firts pair of leaves a bit wavy, probably due to overwatering at some point.

On Day 10 or so, the spans of the first and second pair of true leaves should be the same. This Six Shooter is actually 13 days old which means that its growth has been too slow.

A very sick seedling. Besides yellow, dry, and brittle leaves (due to too aggressive LED light), you may also notice that the second pair of true leaves, though developed, is much smaller than the first one. This assymetry is a clear sign of major trouble.

Green Crack by Fastbuds at day 11 develops nicely. However, there is evidence of mild heat stress.

This 2 week old Auto Euforia seedling has leaves with 1, 3, 5, and even 7 ‘fingers’.

With noticeable side shoots at every node, this young cannabis plant shouldn’t be called a seedling anymore. Now it’s entering the vegetative stage and will develop rapidly.

The Color of Healthy Marijuana Seedlings

Generally, your seedling’s leaves should be medium green, not too light and not too dark. If the green color is too deep, it can mean that there’s too much nitrogen (N) either in the medium (soil mix), or in the plant food that you’re feeding your cannabis.

If the green color is just a bit too dark or too light, maybe it’s the genetics (see below). And when the leaves are turning purple or you see purple veins, purple stem, or even red stem, it also can be attributed to genetics. However, sometimes the cooler temps, especially at night or during the lights-off period, may lead to reddish hues in stem or purple leaves. White stem (usually with some greenish stem color) doesn’t mean there are any troubles.

Yellow is the Color of Trouble

The yellow coloration is a different story. Most often, it’s a sign of trouble, so don’t be complacent and resolve the issue a.s.a.p.

The only exception is when you see yellow veins or yellow in the middle of leaves first thing in the morning. It’s because the growing parts of the seedling haven’t yet been exposed to light. Watch them for a couple of hours, and, most probably, these new leaf parts will produce enough chlorophyll to turn the healthy shade of green.

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This picture was taken at lights on. The new tissue in the middle hasn’t received any light yet, that’s why it’s yellow.

Another case of normal yellowing is when cotyledons die off at some moment. They are necessary in the first few days of a seedling’s life, before true leaves develop. Then cotyledons become redundant, get yellow and dry. This is inevitable and happens sooner if the cotyledons are far from light or shaded by true leaves above them.

This plant is probably 3 or 4 weeks old. The cotyledons have already served their purpose, and now it’s time for them to die.

Marijuana Seedling Identification: How Much Can You Really Tell?

Some people are very impatient to identify their marijuana seedlings. Maybe, you’ve bought a mix of different seeds, and they are not marked in any way, so you can’t tell the difference between them. Or a friend has given you a bean or two, or you decided to try some bag seeds. So, what can a seedling tell you about your future rewards, if any?

Frankly, marijuana seedlings don’t reveal much. The only thing that you can tell with any confidence is whether your seedling is an Indica or a Sativa. Often, you can see the difference in the very first set of true leaves. Indica leaves have darker green color compared to sativa leaves that are more light. Indica leaves are also shorter, broader, and ‘rounder’.

Judging by broad, round leaves, this seedling has dominating Indica genes.

This Green Poison Early version has narrow, light green leaves that point to its Sativa heritage.

The Identification of Sex in Marijuana Seedlings

As for the seedling gender, you can’t tell male from female. Only when a young plant starts flowering, or, to put it more correctly, when it shows preflowers at the nodes, you can determine if they are female hairs or male fists.

This seldom happens earlier than at 3 weeks (in the quickest of automatic strains). For photoperiod varieties, you can only wait until the vegetative growth really kicks in and the first preflowers appear. Alternatively, you can speed up this process by switching your light schedule to 12/12, which can be done even from day one. However, it will be a significant stress for your seedlings if they start flowering like this and then you decide to revert them back to veg with 18 hours of light and 6 hours of darkness.

This plant has clearly shown its sex. It’s a boy. Note that you wouldn’t see male or female flowers in a seedling; only in mature plants.

A much younger cannabis plant has already shown male flowers.

Yet another plant (mature) showing male flowers at the nodes.

This young plant, probably 3 weeks old and not very healthy looking, shows the first white pistils (female hairs) on top. The yellow color in the middle probably means that the picture was taken at lights on.

Identifying a Keeper by Smell

There is one more thing that you can do to understand what you actually grow: you can slightly rub the leaves and smell them. The aroma should be rich and pleasant for you. That’s what breeders do who germinate hundreds of seeds and want to decide early on which ones to keep and which to discard. And, of course, you should look for marijuana seedlings that are healthy and vigorous, not sickly and small.

Not much of identification guide, we know, but it is what it is.

So now you know enough about marijuana seedlings to stop worrying and enjoy the process of growing. And if you want to make sure that your sprouts receive all the proper L&C, check out our article describing the ideal conditions for your weed seedlings and how to take good care of them.

Understanding The Vegetative Stage Of Cannabis

The vegetative phase of cannabis is when the plant grows and gathers its strengths to support buds when flowering.

  • 1. Seedling phase
  • 2. Vegetative phase
  • 3. And what about autoflowers?
  • 4. In conclusion

Cannabis has a number of different stages. The vegetative stage is when cannabis grows leaves and branches to be ready to support and develop the flowers. Like all other plants, has a number of different stages. Cannabis goes through the vegetative and flowering stage before it is ready to be harvested. This article will be dedicated to understanding the vegetative stage of cannabis. We can consider the start of the vegetative stage as soon as the first true leaves appear on our seedling. The amount of nutrients, light, and water your cannabis plant needs will have to be adjusted almost every week since you see the first true leaves until the end of your plant’s life cycle.

1. Seedling Phase

Even though the seedling stage is not considered a part of the vegetative stage, the vegetative stage starts when our seedling starts growing the first true leaves. After germinating and planting your cannabis seed, you will see two small circular leaves growing, these leaves are named Cotyledons and are responsible for feeding the young plant until it is ready to enter the vegetative stage.

The start of the vegetative stage can be considered as soon as the first Cotyledons (first two small circular leaves) appear on your seedling.

The seedling will take a couple of days to completely emerges from the soil and after up to 2 or 3 weeks you will see the first true leaves. Trues leaves are “fingered” leaves, the typical cannabis leaves. Once you see the first fingered leaves, your plant has entered the vegetative stage.

2. Vegetative Phase

After those first true leaves appear, your plant is officially in the vegetative stage. Although this can seem like not a big deal for us, for the cannabis plant it is a huge one.

This means the plant successfully survived the seedling stage and is now using its leaves and sunlight to photosynthesize, and is where growth really thrives. In this stage, your cannabis plant will need a little bit more nutrients (especially Nitrogen) and more water week by week. This along with the help of an 18/6 light cycle it will allow her to start producing sugars and promote growth.

The environment in your growing space should be adjusted for this stage also. You should start at around 60-70% humidity when you see the first true leaves, ending up at around 50% before the pre-flowering stage. The temperature has to be adjusted also and should be between 20-25 Celsius to provide an optimal growing environment for your plant.

If you can provide these conditions, you will see a new pair of fan leaves growing every day, and that is when you can see characteristics of the strain’s lineage. Indicas tend to be short and bushy while Sativas grow tall and with the fan leaves more scattered throughout the plant. When they have grown a little bit and have around 4 or 5 nodes, they’re quite strong, and that is when we can start performing LST techniques. This is because they had time to develop their branches and stem and are not as fragile as they used to be when they were starting to grow the first leaves.

Always be careful not to give your plants too much water or nutrients throughout all your plant’s life cycle but especially during the first weeks of the vegetative stage. Even though their structure is sturdier they are still sensitive. Watering too much, or giving your plant too many nutrients while she’s young can cause her to suffer from nutrient burn and slower growth from overwatering.

By providing a good combination of light, nutrients, humidity, and temperature, you will fulfill your plant’s needs and guarantee a good development of your cannabis plant. This means she will grow healthy, with a good amount of foliage and a strong root system. These are key elements that your plant needs in other to become tough and be ready for supporting the weight of the buds when it’s flowering.

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3. And What About Autoflowers?

Autoflowers don’t depend on the light cycle to grow or flower. Unlike photoperiods that grow under an 18/6 light cycle, autoflowering cannabis strains grow from seed to harvest under the same light cycle, either 18/6, 20/4, or 24/0. This happens because autoflowers contain Ruderalis’ genetics which gives them the autoflower characteristic. But does this mean autoflowers don’t have a vegetative stage? The answer is: No.

Despite not depending on a certain amount of light/darkness to do so, autoflowering cannabis plants go through the same stages as every other cannabis plant, they are the seedling, vegetative and flowering stages, the only difference being that instead of transitioning from the vegetative stage to the flowering stage based on the amount of light/darkness, autoflowers will do so based on their age, which basically means they will start flowering as soon as they’re mature enough to do so. This is why you cannot extend the vegetative or flowering stage of autoflowers like you would do with photoperiodic cannabis strains.

4. In Conclusion

When in the seedling stage, our baby plant it’s still has a nutrient stock in the cotyledons. But after that stock ends and it starts growing the true leaves, it will need new sources of food, that’s where you come in. You have to provide the right amount of food and be really careful about what you feed them and the amount. Even though their structure is becoming sturdier, they’re still sensitive to overwatering and overfeeding. Everything that happens to your plant will have an influence on the final result and especially in how it develops in the next stage, which is the flowering stage. Remember, if we provide an optimal environment, our plant will grow big and healthy, but if we encounter any problems, our plants will have to recover from the shock and that can take a couple of days. The time she takes to recover can result in a smaller plant and can affect the amount and quality of our harvest. So be sure to keep your plans healthy and happy!

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.

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.

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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.