how tall do weed plants grow

If you examine the structure of an indoor cannabis plant at harvest, you’ll often see that there are long fat “colas” at the top, and underneath there are smaller buds. The further down you get on the plant, the smaller the buds are. After a certain point, the buds are so small that they don’t really add any significant weight.

This plant got 12 feet tall in just one summer, with a 3+ foot cola at the top! It received 9+ hours of direct sunlight a day. Unlike an indoor grow light, the size of outdoor plants is limited by the root space and the number of hours of direct sunlight a day!

You can support even taller plants and longer colas under bigger grow lights!

Optimal Plant Height Depends on Your Grow Light. Bigger Lights Can Support Bigger Plants and Longer Buds!

Note: Always try to do an “autopsy” after you grow and take a hard look at your pictures to see if there’s anything you could have done to get even better results! I learn something new every grow!

Now that you have a better idea of the proper plant size and its relation to your grow light (and how to diagnose after the fact whether you should have let the plant get taller or shorter), I’m hoping that some of you will be able to either increase your yields by letting your plants get to the right size, or save time in the vegetative stage by switching to flowering before your plants get bigger than necessary! 🙂

CFLs, T5s and Other Fluorescents – Switch when plant is 6-12″ tall (unless you also have light from the sides, then it can be a bit taller as long as all the bud sites are getting light) 250W HPS – Switch when plant is.

This was the longest solid cola I’ve gotten from a 250W HPS grow light; it was about 12″ long. Below that point, the plant still made buds, but they were individual buds as opposed to a long cola. The final height of a plant should generally be about twice the height of your longest main cola . That tends to be the “sweet spot” for a lot of strains.

Another example of plants that were a great height at harvest!

Although it’s true you want to flip to the flowering stage when your plant is about half the final desired height (since it will about double in size after the flip to the flowering stage), here are some general guidelines that have worked well for me:

So What’s the Best Plant Height?

If nothing else were changed, the yields would not be that different whether the plant is 2 feet tall or 4 feet tall under a 250W HPS, because the light doesn’t go down that far into the plant. However, a bigger grow light could have supported a taller plant.

Notice how small the buds are at the bottom of this next plant. If it had been allowed to get much taller it likely wouldn’t have produced significantly more yields, but it would have taken extra time in the vegetative stage. This is an example of what the plant should generally look at harvest like if it’s the proper height – about twice the height of the big buds on top, with significant but small buds at the bottom! It could have been a little shorter and probably not lost any yield, but definitely an example of a good final height!

Is there an Optimal Final Height for the plant? Most everything I read says to continue the Vegetative Stage until the plant is about 1/2 its desired height, then flip to Flowering Stage, because plants about double in height on average. Assuming you are keeping the canopy as flat as possible. Should you try for as tall as your tent/light will allow without burn? Or is there an optimal height found to give best yield/quality? Does the plant waste energy moving the nutrients up a taller plant? I see amazing pictures of bountiful plants that appear to be under 36″, with lots of fat dense colas.

Note: Defoliation (removing leaves to expose bud sites) lets you produce bigger buds further down into the plant! That means your light could potentially support slightly taller plants with longer buds if you use defoliation. This is why it’s important to always test your plants with your light and your setup, as everyone’s results will be a little different based on their strain, environment and personal growing techniques.

“Tall” vs “Short” Strains.

Under a 600W HPS, I haven’t ever seen a main cola that’s much longer than 2 feet even if light is getting down almost to the floor. So, I’m not sure how much benefit you would get by switching to 12/12 after the plant is 2 feet tall. These plants were switched at around 20″ tall under a 600W.

This plant was under a 1000W light and has huge, thick, arm-sized buds that go basically to the bottom of the plant. These buds are so thick at the bottom where they end that it’s good evidence this plant would have produced quite a bit more bud if it had been allowed to get taller in the vegetative stage. Those colas would have been longer, and there would have been many chunky buds underneath. This plant should probably have been about twice the height (twice the size of the longest cola) to have really produced what it was capable of under this grow light. But the grower still had a whole lot of bud to console himself with 🙂

Root space is more critical outside and with soil than indoors or with coco or hydro. Root space for outdoor plants is usually provided with big fabric pots (600+ gallon containers in some cases!) or with raised beds full of good soil.

15″ tall, and a 630W is good for.

Big buds form on top, but as you get further from the light, the buds get smaller until there are almost none. If these plants had been allowed to get any taller (with everything else the same), they likely wouldn’t have produced much more bud than they did here. Any extra time spent in the vegetative stage likely would have been a waste of time.

This is especially true for indoor growers, where you are in charge of nearly everything. When growing outdoors , you still have a bit of control over plant height, but you are also at the mercy of the sun and the elements.

Strain – Some strains tend to have shorter lives, and others need longer before they're ready to harvest. For example, you can choose to grow an auto-flowering strain to get to harvest in as short as 8 weeks. But many strains which originated near the equator can take months and months before their buds are ready to harvest, even when growing indoors. So strain is important when it comes to time-to-harvest.

To learn about all the tools and techniques you have available to control the height and shape of your plant, take a look at our Plant Training & Height Control guide!

And super cropping is just one technique to getting seriously killer harvests. If you want to learn ALL the secrets…

How long will my marijuana plant take to grow? How long from seed to harvest?

Discover Exactly How Long It Takes Before You Get to Harvest.

How tall will my marijuana plants get?

Get Instant Access to It All Right Here: GrowWeedEasy.com/growing-elite-marijuana.

Growing Method – soil tends to be the slowest growing medium, and hydro tends to create the fastest growth.

How long will it take?

Although it isn't the be-all end-all when it comes to size, strain is still definitely something to keep in mind when it comes to height. Although you can control the exact height and shape of your plant no matter what the strain with plant training, different strains grow differently and you want a strain that makes it easier to get the results you want. When growing with bagseed (seeds that you find in your buds) you often don't know what to expect until the plant actually starts growing.

You can achieve almost any size or shape when growing indoors as long as you use plant training. But if a cannabis plant is left to grow outside with tons of sun and without any plant training, the sky is the limit for how big they can get!

Plants can be grown shorter than your knees , or taller than your house .

For example, some strains (known as "indica" strains tend to stay short, while "sativa" strains tend to grow tall). Just to give you an idea of the difference, these plants were grown in the exact same setup.

Question: How tall should I expect my marijuana plants to get? And how long does it take until harvest?

To fight these natural tendencies and force these plants to be the same height, the grower would have needed to use different techniques and training strategies. If the grower had wanted to make the right plant shorter, the plant would have needed more Low Stress Training and Supercropping.

How tall will it grow?

Get the answers below!

Learn more about how to get your plants to grow the size and height you want!

Learn from the best!

I thought I already knew it all, but after I went through this grow bible, I discovered that there were still lots of easy ways I could increase my yields and grow even more potent buds! I find myself going back to it again and again for new ideas.

Be mindful to increase your watering as the plant develops. When it’s young, your plant will need water close to the stalk, but as it grows the roots will also grow outward, so start watering further away from the stalk in the soil so roots can stretch out and absorb water more efficiently.

Buds typically grow the most toward the end of the flowering life cycle. You probably won’t notice much budding out at the beginning of the flowering stage, and it will slow down toward the end of the cycle, when buds become fully formed.

Cannabis plants are considered seedlings until they begin to develop leaves with the full number of blades on new fan leaves. A healthy seedling should be a vibrant green color.

Harvest happens sometime between September and November. This depends on your local climate, as well as the weather that particular year—one year it could be the end of September, the next, end of October, and growers in the Pacific Northwest will have to pull down their crops earlier than those in Northern California.

The growth stages of marijuana can be broken down into four primary stages from seed to harvest:

Vegetative stage.

We can’t stress enough that the timeframes in the above graphic are ranges of time for the Northern Hemisphere. You’ll need to adjust them based on your specific region and local weather and climate.

As roots develop, the stalk will rise and you’ll begin to see the first iconic fan leaves grow, at which point your cannabis plant can be considered a seedling.

The flowering stage is the final stage of growth for a cannabis plant. This is when plants start to develop resinous buds and your hard work will be realized. Most strains flower in 8-9 weeks, but some can take even longer, especially some sativas.

As the sun reaches up high in the sky, your cannabis will want to as well. Make sure all of your plants are outside by the Summer Solstice.

Within the flowering stage, there are three subphases:

Be sure to keep a grow journal to track the progress of your plants. Looking back on your notes will help you learn from mistakes and maximize the quality and quantity of your buds.

Cannabis plants go through a series of stages as they grow and mature, and those different growth stages call for different amounts of light, nutrients, and water.

Seed germination length: 3-10 days.

If you need to determine the sex of your plants (to discard the males), they will start showing sex organs a few weeks into the veg stage. It’s imperative to separate males so they don’t pollinate the females.

The Spring Equinox is a good reminder that it’s time to kick off the outdoor growing process and start germinating your seeds.

Flowering stage.

Marijuana light cycle: 16 hours a day.

Vegetative stage length: 3-16 weeks.

Outdoors, flowering occurs naturally when the plant receives less light each day as summer turns into fall. Indoor growers can trigger the flowering cycle by reducing the amount of light marijuana plants receive from 16 to 12 hours a day.

There are a number of changes to consider once plants go from the vegetative stage to the flowering stage:

The vegetative stage of cannabis is where the plant’s growth truly takes off. At this point, you’ve transplanted your plant into a larger pot and the roots and foliage are developing rapidly. This is also the time to begin topping or training your plants.

Flowering stage length: 8-11 weeks.

If you’re growing outdoors in the Northern Hemisphere, growers usually get their seeds between February and April, and you should start your seeds by the end of April. Some growers will start their seedlings inside in a more controlled environment because seedlings are more delicate, and then put their seeds in the ground outside once they’re a little bigger. If you’re growing clones or autoflowers, you have a grace period of another month or so. Plants usually need to be outside, in the ground, by the end of June.

What are a weed plant’s growth stages?

Seedling stage length: 2-3 weeks.

Once your seed has germinated , or sprouted, it’s ready to be placed in a growing medium, like soil. The tap root will drive down while the stem of the seedling will grow upward.

When your marijuana plant becomes a seedling, you’ll notice it developing more of the traditional cannabis fan leaves. As a sprout, the seed will initially produce leaves with only one ridged blade. Once new growth develops, the leaves will develop more blades (3, 5, 7, etc.). A mature cannabis plant will have between 5 or 7 blades per leaf, but some plants may have more.

At this stage, the plant is vulnerable to disease and mold. Keep its environment clean and monitor excess moisture. Be sure to give it plenty of light.

The biggest variability in how long a marijuana plant takes to grow will happen in the vegetative stage—after the seedling phase and before flowering.

Marijuana light cycle: 16 hours a day.

Take meticulous notes on when and how you perform each step, as well as what the weather is like. Other notes can include how much water you give plants, at what intervals, and how much nutrients you give them. Pictures will also give you a better sense of how your plants look along the way.

If you’re growing weed indoors, you can grow whenever you like. Keep in mind that the outside environment will affect your grow space—you may need to add heaters in the winter or fans and ACs in the summer. Other than that, you can start seeds whenever you like and flip them into flower whenever you like, depending on how big you want the plants.