What is the ideal height of your cannabis plant?
Your seeds can grow into a huge cannabis plant. What is the ideal height ?
When we talk about growing cannabis indoors, at best you want to have as many flowers as possible. But then the question arises how tall the plant should be in order to have the largest possible yield. This is not only the right choice of variety made directly for indoor, but also the light source.
Small x Large varieties of cannabis plants
Most cannabis plants double in height / size as they enter the flowering stage. However, there are varieties that “pull out” more or less than you know. If you want to buy cannabis seeds and indoor varieties specifically, always go through all the information about the variety.
“Higher variety” – go to the flowering stage a little earlier (1/3 of the required height).
“Lower variety” – In this case, you should wait a little longer before entering the flowering phase (3/4 of the required height).
The stronger your light is, the taller you can make the plant. With weaker lighting the plants can also be tall, however the usable buds will be mostly from the tops. It is advisable to use defoliation in the case of tall plants under the weak light.
Also, if you switch to bloom very young plants or fresh rooted clones, it can shoot up to four times its height. Especially sativas with little branching are capable of incredibly vigorous growth after switching.
The reason is that the plant is trying to catch up with its genetic predispositions.
What is the best height?
In the end, it is not precisely determined what the ideal height is. When growing, it will always depend on your equipment and methods.
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 ~12″ tall
- 400W HPS– Switch when plant is ~17″ tall
- 600W HPS– Switch when plant is ~21″ tall.
- 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 ~22″ tall)
- LED Grow Lights– Unfortunately, this depends a lot on the model. It’s partially a matter of trial and error because there’s no “standard” with LEDs like there are with other grow lights. A good rule of thumb is to take note of the length of your main colas after the switch to 12/12 (from a previous grow), then try to initiate flowering with your new plants when they’re about that height. So, if your main colas end up around 12″ long, initiate flowering when the plant is 12″ tall, etc. But if you aren’t sure yet, I recommend just sticking to the “half the final desired height” rule with LEDs, because that ensures that at least the plant will fit in your grow space and you’ll be able to learn what to expect from your LED model.
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! 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.
How to Control Height of Indoor Cannabis Plants
This cannabis height control tutorial will teach you how to use bending and training techniques made specifically for cannabis plants (such as LST / low-stress training, supercropping, topping, FIMing, ScrOG, or using a screen or netting, etc.).
It’s easy to control marijuana plant height, but you need to understand 3 things. Once you understand these three principles, you’ll be able to force indoor plants to grow into the exact shape and size that you want.
- Setup – Choose the right setup (pot size, grow medium, grow light, strain) to naturally help produce plants the size you want – details below
- Plant training – Learn how to force plants to grow flat and wide instead of tall (or whatever shape you want), and discover techniques to reduce the size of out-of-control plants
- Flowering stretch – Understand how plant height is affected in the flowering stage and how to use this to your advantage.
Let me go through those quickly. Soon you’ll be able to create plants in whatever size you want
The setup you use can actually cause plants to grow taller than necessary. Here are some things to keep in mind.
Pot size – Smaller pots (restricting root size) will help keep plants smaller. They can still get big if you keep them watered and happy, but it will take them longer to get big compared to a plant with unrestricted roots. For example, if given the exact same conditions and amount of time, 1-gallon pots tend to keep plants small, 3-gallon pots tend to produce mid-size plants, while 7-gallon pots can produce humongous plants indoors. I usually grow with 1 or 2-gallon pots in a mini tent, 3 or 5-gallon pots in a 2’x4′ grow tent, and 5-gallon pots in a 4’x4’x6.5′ grow tent. Note: smaller pots need to be watered more often so there is a tradeoff.
Smaller pots tend to keep plants smaller, bigger pots tend to result in bigger plants
Grow medium – Plants tend to stay a little smaller in soil (especially when grown without nutrients in a “just add water” setup) vs in coco or especially hydro.
Grow light type – Choose a type of grow light that tends to keep plants short
- Best:LEDs and MH (metal halide) grow lights tend to keep weed plants shorter. MH should only be used in the vegetative stage so LEDs are one of the best choices to use from seed to harvest if you want to keep plants short.
- Okay: Fluorescent lights like T5s or CFLs must be kept extremely close to plants to prevent them from “stretching” tall towards the light. However, if the light intensity is high enough, plants will stay short.
- Worst:HPS and CMH/LEC grow lights (especially when using a Bloom/3k bulb) produce extra height in less time. These grow lights tend to cause plants to grow tall and stretchy (with lots of stem between each set of leaves) in the vegetative stage, as well as in the flowering stage to a lesser extent (though both types of light reward you for your trouble with incredible bud yields and density)
Good LED grow lights help prevent stretchy plants
Grow light spectrum
- Blue light is usually listed between 4000k-6500k as the color of the grow light spectrum (if you see nanometer measurements for individual diodes, blue is in the 450-495nm range) tends to keep plants shorter and bushier. Often the grow light or bulb will say they’re best suited to “vegetative” growth. They tend to get smaller yields when used in the flowering stage, though they can help increase “sparkle” (trichome production) on buds.
- Red light is usually listed between 2500k-4000k as the color of the grow light spectrum (red is in the 625-750nm range) tends to cause plants to grow more stretchy and tall. Often these are listed as “Bloom”, “Flowering”, or “Red Spectrum” grow lights. In the flowering stage, they produce higher bud yields.
- Mixed spectrum – These lights contain a mix of everything and give you a mixture of effects depending on the ratio.
Using an LED with high amounts of blue light (like this HLG 300 B-spec) designed for the vegetative stage helps encourage plants to grow short and bushy instead of tall and stretchy, though yields tend to be a bit smaller if you don’t switch to a flowering grow light for the flowering stage
Grow a Short Strain – Some strains tend to stay short while others tend to get tall no matter what you do. In general, autoflowering strains tend to stay smaller, but over the last few years I’ve noticed many of the newer strains can still get alarmingly big unless specifically listed as a “short strain”.
Choose a good setup to grow short plants. For example, mini tents with tiny grow lights can be surprisingly productive when you recommended supplies and instructions in the mini tent setup tutorial. This grow produced over 5 ounces with an HLG 100 V2 (R-Spec version) and 4 plants in 2-gallon fabric pots.
Note: As you can see with the mini tent example above, as long as you follow the rest of the instructions you can still keep plants short with a bloom grow light from seed to harvest.
Auto-flowering strains that tend to stay short
– Classic effects that are relaxing but not overwhelming, easy to grow, and smells amazing – Purple buds, fast finishing, easy to grow, average-to-high potency – Fuel or gas smell, high potency, “uplifting” and “creative” psychological effects are excellent during the day – Resistant to problems, buds sparkle, very high potency – Distinctly Californian sweet smell, high potency, “body high” and “heavy” effects are a great way to end a long day
THC Bomb Auto plants tend to stay short and produce above-average potency and yields
Photoperiod strains that tend to stay short
– Beautiful sparkly buds, hint of bubblegum scent, good yields, high potency – Exceptional sweet smell and taste, easy to grow, very high potency (Royal Queen version) – Great yields, easy-going, quick time to harvest, high potency but not overwhelming effects – Easy to grow, quick to harvest, old school chill classic 90s effects with an extra kick – Buds take on purple tints, excellent smell, potent and long-lasting effects (King Tut) – Relatively low smell (which may be better for stealth), extra high potency
Tutankhamon plants don’t have a strong smell, which may be a good thing in a stealth setup. This grower used plant yo-yos to hold up heavy branches.
2.) Plant Training
Use bending and tie-down techniques on cannabis plants from seed to harvest; it’s the easiest way to control height. The idea is simple:
- Top plants (cut off the top) when they are small to make plants naturally grow more wide and bushy. A good time to cut off the top is when the plant has about 6 sets of leaves.
- Bend over tall branches and tie them down – When any branch or stem starts getting significantly taller than the other branches, gently bend it down and away from the center of the plant. Tie it in place using something like plant twist-ties attached to your plant pot (bend twist-ties around the lip of the plant container, or poke them through a fabric pot).
- Use the cannabis-specific supercropping technique if you need to bend a branch that is already hardened and would normally break if you try to bend it.
Check out our simple cannabis plant training guide for complete instructions. This can be used in any setup. Or check out the mini tent tutorial if you want directions to grow in a mini tent.
This plant is in a 3-foot tent (shorter than my waist), yet still produced several ounces of bud under an HLG 65 4000k (blue spectrum 65W LED grow light, highly recommended for small spaces). Check out the full mini tent tutorial if you want to copy this grow style at home.
Here’s that plant at harvest. Still short, just covered in buds.
Side view at harvest – 18″ (46 cm) tall
This is me holding that plant as the buds fell over from the weight
Check out the full mini tent tutorial for step-by-step instructions and pictures on how I trained this plant (it’s easy to copy these results once you know what to do).
3.) Flowering Stretch
It’s important to understand that cannabis plants will about double in height on average after they start flowering (making buds). This is often referred to as the “flowering stretch.” Not being prepared for this growth spurt is often the root cause of height trouble for many marijuana growers. If you wait until your plants are the right height and then initiate flowering (give plants a 12/12 light schedule on a timer to imitate late summer nights), you will end up with plants that are twice the size you wanted. No good.
Here’s how to make the flowering stretch work for you:
- Cannabis plants get significantly taller after they start flowering. Therefore you want to initiate flowering when they’re about half the final desired size.
- A general rule of thumb is cannabis plants double in size after they started flowering. However, strains listed as “short” tend to stretch less, or not much at all. Strains listed as “tall” may triple in height or more.
- If you initiate flowering on a plant that’s less than 4 or 5 weeks old, it tends to stretch more because it takes longer to start flowering so the “stretch” lasts longer
- Topping plants when they’re young and training them to grow multiple branches (as explained in step 2) reduces the amount of height gained during the flowering stage because this spreads out the upward growth between multiple branches vs having all the height go into one main stem. (removing leaves in a strategic way) and supercropping (bending thick stems) during the flowering stretch tend to slow upward growth.
- When you’re adding nutrients to the water, plants tend to grow faster (stretch more) than if they’re living off the nutrients in the soil.
Let’s go through some real-life examples of flowering stretch to help give you an idea of what to expect. I wish I had seen this when I started growing as it would have saved me some height headaches.
Strain makes a big difference when it comes to final cannabis plant height after the flowering stretch. These two plants were grown in identical conditions but were two different strains. This is what they looked like after some plant training. You can see the plant on the right already wants to be tall. I started giving a 12/12 light schedule right after this picture to switch the plants to the flowering stage.
Here are the same plants at harvest. The left plant is a “short” strain and barely stretched. The right plant is a “tall” strain and doubled in height.
3 Weeks Old
These cannabis plants were 3 weeks old when I initiated the flowering stage by giving a 12/12 light schedule. Since these plants were still young, I knew they could more than double in height. Young plants take longer to start flowering and tend to stretch more.
Their height at harvest (about 3x height after the stretch)
4 Weeks Old
I initiated this 4-week old plant to start flowering at this height
It ended up about 2.5x height after the flowering stretch was over
12″ tall – super soil (no nutrients)
These soil-grown plants (grown in “just add water” super soil without nutrients) are about 12″ (30 cm) tall when flowering was initiated.
Here are those plants at harvest. They ended up about 20″ (50 cm) tall after the flowering stretch. They grew taller but didn’t quite double in size. Cannabis plants tend to stretch less in soil without added nutrients.
12″ tall – coco coir (using nutrients)
Plants grown in coco or hydro with nutrients tend to stretch more. These plants are clones of the above plants, in the same setup, which were also initiated to start flowering at about 12″ tall. However, these plants were grown in coco with nutrients.
The coco plants were significantly taller at harvest, about 30″. So they more than doubled in height even though everything else was the same except the grow medium and using nutrients. Just something to keep in mind if you’re trying to keep plants short. However, these were in 5-gallon pots. I’ve found small pot size helps reduce flowering stretch especially in coco.
Flowering starts too late (untrained)
Here’s an example to show what happens when you don’t do any training and flowering starts too late. These plants are autoflowering strains which means that flowering starts on its own automatically after 3-6 weeks (everything else is the same as standard/photoperiod strains). The plants were left to grow naturally without topping or training and this was their natural shape. The tallest plants were 24″ tall when flowering started.
Check out the insane flowering stretch. At harvest, the plants had grown into these beasts. This also shows how some strains “stretch” more than others. I hope this helps illustrate why it’s important to choose “short” strains and start flowering at the right time. It also demonstrates what can happen if you don’t use any bending and training to control height during the vegetative or flowering stage (I was pretty shocked by this).
Trained to stay short and flat
The sister plants to those out-of-control plants (same strains in a different tent) show the power of training to reduce the flowering stretch. These plants were trained to be short with multiple branches per plant (instead of just one main trunk like the above example). Not only does this keep plants shorter overall, but it also reduces the amount of height gained during flowering since the upward growth gets spread between many branches at the same time.
I did have to do a little more bending as they grew, but you can see at harvest how much better the height was controlled. I would have been able to grow these plants in a significantly shorter space while the other tent was overflowing. Bonus: These plants actually yielded more weed than the ones in the untrained tent. Plant training not just controls height but can increase yields significantly by forcing plants to grow many big buds instead of just a few.
Summary: How to Control Cannabis Plant Height
Remember these 3 things
- Setup – Choose the right pot size, grow medium, grow light, and strain to naturally help produce plants the size you want
- Plant training – Force plants to grow flat and wide instead of tall
- Flowering stretch – Understand how plant height is affected in the flowering stage and use this to your advantage.
You now have the understanding you need to become an expert at cannabis plant height. Time to grow topiary-level cannabis plants with great yields!