What is the Optimum Final Height for Cannabis Plants?
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.
When it comes to training cannabis plants indoors, in the best-case scenario, you want your plants to be big enough to support as much bud as your grow light can produce. There’s no point in having a whole bunch of bud sites located below where light can reach because buds that don’t get any light tend not to fatten up. So, when growing indoors the optimal length of buds is heavily dependent on your grow light.
Optimal Plant Height Depends on Your Grow Light. Bigger Lights Can Support Bigger Plants and Longer Buds!
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.
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 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.
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.
A too-tall plant isn’t a big deal if it fits in your grow space, but the extra lower growth that doesn’t produce bud is essentially a waste of electricity, time and money, since you potentially could have shaved weeks off your vegetative stage without sacrificing yields!
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.
You can support even taller plants and longer colas under bigger grow lights!
Examples with Common Grow Lights
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:
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!
- 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
400W HPS– Switch when plant is
600W HPS– Switch when plant is
LEC or CMH Grow Lights– Follow general guidelines for HPS lights based on your wattage (a 315W is good for
15″ tall, and a 630W is good for
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
Although plants typically double in height after the switch, some particularly tall and short strains can stretch more or less than average! Always pay attention to what the breeder tells you about your strain and plan accordingly!
- If you have a “tall” strain, switch to the flowering stage earlier than recommended (1/3 the final desired height)
- With a “short” strain you should wait until the plant is taller before the switch (3/4 the final desired height), to ensure the plant is tall enough after it’s done stretching.
In the picture below, the grower could probably have switched to 12/12 earlier without hurting yields because the buds at the bottom are not adding much weight. Sativa plants like this can triple in height after the switch to the flowering stage, so it’s common to end up with a Sativa plant that’s far taller than expected!
Optimum Cannabis Height Outdoors?
Height restrictions are much different for outdoor plants that mature under the powerful light of the sun. Outdoors, plants can keep getting taller and taller as long as they get enough direct sunlight a day and have enough root space.
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.
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!
So What’s the Best Plant Height?
Ultimately, there is no “right” or “best” height for a cannabis plant, and like most things when it comes to growing, it depends a lot on your setup. I’ve given you some general ideas of what to aim for and what to expect, but it’s also very simplified. Unfortunately, there’s no single formula that fits every growers setup. But the following pictures will hopefully help give you some ideas!
Check Out Examples of Cannabis Plants That Are Too Tall, Too Short, or Just Right!
This marijuana plant got excellent yields for its size under a 600W grow light, but notice how the buds are thick all the way down. This is a clue that this plant likely would have produced more if it’d been allowed to get a little bigger before switching to the flowering stage – you can see the buds “want” to go down further than the bottom of the plant. Additionally, there is empty space behind and to the left side of the plant. If the plant had been trained to grow wider in the vegetative stage, those empty spots would be full of colas, too!
In this example, the plant was “lollipopped” (the lower part of the plant was stripped of leaves and bud sites before being switched to the flowering stage). However, on the parts of the plant that weren’t stripped, you can see significant buds going a lot further down. This plant likely would have yielded even more if it’d been allowed to keep more bud sites. The grower could have still stripped all the leaves, but they may have gotten better results if they’d left bud sites for at least a few more inches if not all the way to the bottom.
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!
Here’s another example of a plant that was a good height at the end. You can see there isn’t a whole lot of extra growth at the bottom with small buds. However, you can see the buds end where the thick layer of leaves begins. This grower could have used some light defoliation to expose more bud sites lower down, and produced buds further down into the plant. In that case, their grow light could possibly have supported a plant that was even taller!
Another example of plants that were a great height at harvest!
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 🙂
What to Remember About Plant Height
- The optimal plant height before flowering is about the length of your “main” (solid) colas. For your first couple of grows, you’ll have to guess (and I gave some guidelines above to help get you started), but after some experience with your setup you’ll be able to dial it in perfectly every time as long as you do strain research first.
- Increasing overall plant size and number of bud sites in the vegetative stage (while staying the proper height) will increase number of colas and ultimately yields.
- Training the canopy to be flat, yet wide enough to fill the entire space under the light ensures all cola are a good distance to the grow light in the flowering stage.
- Letting plants get taller than your light can support will result in wasted time in the vegetative stage!
- Defoliation lets you produce bigger buds further down into the plant by exposing more bud sites to light!
- Again, 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! 🙂
P.S. One Last Thing About Plant Size…
In addition to the height, the overall size/mass of the plant has a big effect on final yields. A bigger plant can simply support more and bigger colas. Because of that, it’s good to build up overall plant size as opposed to just height to maximize yields. You want plants that are wide and flat like a table, not tall and skinny!
Many indoor growers let their plants get bigger horizontally while restricting the plants’ ability to grow taller than the grow light can support. This lets you keep adding more and more bud sites without letting the plants get too tall.
In addition to making sure your plants are the proper height, you also want to train your plant canopy to be flat and wide before switching to the flowering stage. The best yields are achieved by filling the entire grow space front-to-back and left-to-right with a flat canopy because it lets all the buds be close to the grow light.
Maximize your yields by filling your grow space with colas!
Too-tall cannabis plants waste time and electricity, but too-short plants end up hurting yields! Learn how to find that perfect sweet spot for plant height!
How tall will my plant grow? And how long will it take?
Question: How tall should I expect my marijuana plants to get? And how long does it take until harvest?
How long will it take?
How tall will it grow?
Get the answers below!
These are very common questions for new growers, so let me give you the straight answers…
How long will my marijuana plant take to grow? How long from seed to harvest?
It will be 8 weeks – 6+ Months before your plants are ready to harvest.
But that’s a huge range, right?
The truth is, the time to harvest depends on your growing method, whether you grow inside or outside, your strain, and your desired yields…
Growing Method – soil tends to be the slowest growing medium, and hydro tends to create the fastest growth
Inside or Outside – In general, outdoor plants need longer to harvest than indoor plants. Outdoors, you plant in the spring, and harvest in late fall, taking 5-6 months or more. Indoors you have more control over the plant and can choose how long you want your plants to grow before harvest, and can get to harvest in just a few months. Indoors you can also start growing at any time (you don’t have to wait until Spring to start growing).
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.
Desired Yields – If you want bigger yields, you need a bigger plant, and that takes more time to grow than a small one.
Discover Exactly How Long It Takes Before You Get to Harvest
How tall will my marijuana plants get?
Plants can be grown shorter than your knees, or taller than your house.
Basically you (the grower) are in complete control of how tall your cannabis plants grow.
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.
Some strains tend to grow tall and thin, while others tend to grow short and squat, but you can force your plant to grow differently when growing cannabis indoors. In fact, you have many options to control the exact shape and size of your plant.
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!
Short plant in a small space – this plant is only about two feet tall thanks to training with a screen, yet still producing lots of bud! You don’t need a huge space to get a good harvest when you use plant training.
These cannabis plants were also trained to stay short, this time using LST – they were under two feet tall at harvest and produced more than 6 ounces of bud under a small grow light!
These plants were trained using manifolding. They were about 5 feet tall at harvest, and produced more than a pound of bud!
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!
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.
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.
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.
For the left plant to grow taller, the grower would have needed to give the plant more time, since indicas tend to stay short. So even though you can force plants to grow into any size and shape, it’s often easier to start with a strain that naturally grows the way you want. That way your plant is working with you instead of against you. Learn how to find the right strain for your needs.
Learn more about how to get your plants to grow the size and height you want!
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About Nebula Haze
In response to the need for more tutorials aimed at new growers, Nebula co-founded GrowWeedEasy.com in 2010 with fellow grower Sirius Fourside.
Since then, Nebula has published hundreds of growing articles in print and online, and continues to dedicate herself to serving the medical marijuana growing community.
“My mission is to show other medical marijuana patients how easy it can be to grow weed out of your closet.”
[Answer inside!] These are very common questions for new growers, so let me give you the straight answers…