What is the purpose of large "fan" leaves?

Betrion

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Hello girls and boys!

Reading the forum, I realized that a lot of people cut leaves here, so I decided to copy something from the Croatian forum and share it with you, so whoever is interested should read it.


What is the purpose of large "fan" leaves?

Large "fan" leaves have a specific role in the growth and development of Cannabis. They serve as "photosynthetic factories" for production
sugar and other substances necessary for growth. Most Cannabis plants begin to lose their large "fan" leaves when they enter the flowering phase
this continues until the harvest, i.e. the death of the plant.

"Fan" leaves comprise the largest surface area for photon reception on the plant, therefore they do most of the photosynthesis that takes place in the plant. The cells in the plant's leaves, called chloroplasts, contain a green pigment called chlorophyll, which, with the help of the sun, separates the water in the plant into its basic elements. 15% of the solar energy that falls on the leaf is absorbed, while the other 85% passes through the leaf that reflects green light, which makes it seem as if not much light reaches under the leaf, because human eyes are most sensitive to the green spectrum.

Photosynthesis takes place in all green parts of the plant. The process consists of two phases, the light primary reaction and the secondary reaction (Calvin cycle), which convert water and carbon dioxide into sugars and oxygen. These sugars are later used as energy for all processes in the plant, including the synthesis of THC and other cannabinoids.

"Fan" leaves contain the largest number of stomata, these are tiny "holes" on the underside of the leaf through which the plant receives carbon dioxide and oxygen, which are used for photosynthesis and respiration and transpiration. Carbon dioxide first enters the leaf through the stomata and combines with the energy stored in the chloroplast through a chemical reaction (Calvin cycle).
thus forming a simple sugar. This sugar is then transferred to the tissue and transported via channels/"tubes" in the leaves to other parts of the plant that need this food for work, growth and development. (young leaves, roots, flowers...)

Removing the "fan" leaves will not only slow down growth, but will also interfere with the plant's ability to get rid of toxic substances, and also interfere with the plant's temperature regulation that takes place through the stomata. The changes in the plant's chemical metabolism caused by the removal of "fan" leaves forces the plant to do extra work to get rid of the "toxin" with less leaf mass, resulting in the plant being able to allocate growth hormone to producing new leaves to replace what is lost. There is a connection between the amount of carbohydrates produced by the leaf and CO2 intake in relation to external influences. In a situation where a leaf is no longer productive for the plant, for any reason (poor light, age, disease, insects, etc.), the plant will reject that leaf.

Plants and leaves are dotted with veins that serve to transport nutrients and products of photosynthesis throughout the plant. In the vein there are channels called xylem and phloem. Xylem is the conductive part of the plant through which water with nutrients travels from the roots through the stem to the leaves and flowers, and phloem is the conductive part of the plant through which the products of photosynthesis (sugars, hormones, proteins, etc.) pass from the leaf to other parts of the plant.

Every part of the plant can be a source or consumer of sugar.
Phloem transports energy from the source (area of production) to the consumer (area of conversion/metabolism or storage). There is no doubt that flowers can produce some photosynthate, but they are not nearly as efficient as "fan" leaves (trichomes greatly reduce the absorption of light into the tissue they are on). So flowers are consumers and leaves are energy producers.

The leaves on the upper part of the plant tend to supply food for the growth and development of (new) tops.
The leaves on the lower part of the plant tend to supply food for the growth and development of the roots.
The central leaves supply the entire plant depending on where the demand for energy is greater.
During flowering and ripening, only the lowest leaves supply the roots, while all the others try to deliver as much energy as possible to the flowers. For this reason, the more leaves that are out of the shade and in direct light, the better chance the plant has for creating additional energy reserves that will ultimately contribute to a better harvest.



When and how to prune and if at all.

Remove unproductive wilted leaves.
Aging leaves that have reached their maximum size will stop producing chlorophyll and begin to fade, in most cases turning yellow and the petiole turning purple. Then the leaf's ability to produce sugar declines, and those leaves are the ones that should be removed first to let light pass to new leaves that produce energy in greater quantity.
Older leaves, although larger in surface area, are no longer as productive when they begin to lose their green color, i.e. chlorophyll.
In outdoor cultivation, the leaves have an additional, very important purpose of protecting the plant from inconveniences and pests.
So it's mostly the leaves that are the first to be damaged, after which they die and fall off.

What you need to pay attention to are the reasons for the premature discoloration and death of the leaves, and try to correct any mistakes that led to this condition, since this negatively affects growth and development to a much greater extent than a couple of "extra" leaves would ever affect.

In the last 14 days, you can remove the leaves to speed up or avoid washing before harvesting.
Which, in my opinion, is nonsense because any possible gain in drying and curing speed does not justify the stress and slow development that the plant will experience in that case in its final and perhaps most important phase.


How to circumcise if you decide to.

In this case, you trim the leaves by cutting them in the middle of the petiole, either with scissors or a squeeze
between the fingers, i.e. with the nails. Thus allowing the rest of the stem to dry out and fall off on its own.
This will help protect the plant from infection. The leaves should not be torn off completely with the base of the petiole
because this way the stem is more exposed to possible infections.
 

WeedHopper

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I trim them off all the time if they are in the way of my buds getting sun
 

bigsur51

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good post!


In this case, you trim the leaves by cutting them in the middle of the petiole, either with scissors or a squeeze
between the fingers, i.e. with the nails. Thus allowing the rest of the stem to dry out and fall off on its own.
This will help protect the plant from infection. The leaves should not be torn off completely with the base of the petiole
because this way the stem is more exposed to possible infections.

this is what we do and it’s a good practice

otherwise , in a lecture in my Plant Science class , the Professor stated that most plants can lose up to 30% of their leaves and it will have little to no effect on photosynthesis
 

CrashMagnet

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Just from observation, when I clean up a plant with "excess" leaves and leave its sisters unpruned, it grows faster than they they do. I don't know if the end result is more or bigger buds, though. I always end up with other more significant issues affecting plant growth during flower, like nutrient deficiencies, bugs, etc.

Anyway, leaf cover that's too dense can block air flow and hold in moisture making the plant more susceptible to mold, especially during flower.
 

bigsur51

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ditto…..I’ve done side by side , trim the heck out of one plant , leave the other to bush out

i have really noticed very little change in the plant as far as yield goes…they both produced about the same amount of herbs , the difference was negligible

the benefit that I see by defoliation , besides better air flow , is there is less trimming to do around harvest time!

we are not to worried about air flow and mold around here because it is so dam dry

in fact , we need bushy plants to help keep the moisture in and around as long as possible or else it evaporates and things can dry out really fast with 10% humidity

everyones milage will vary depending mostly on geography and genetics
 

RosterMan

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ditto…..I’ve done side by side , trim the heck out of one plant , leave the other to bush out

i have really noticed very little change in the plant as far as yield goes…they both produced about the same amount of herbs , the difference was negligible

the benefit that I see by defoliation , besides better air flow , is there is less trimming to do around harvest time!

we are not to worried about air flow and mold around here because it is so dam dry

in fact , we need bushy plants to help keep the moisture in and around as long as possible or else it evaporates and things can dry out really fast with 10% humidity

everyones milage will vary depending mostly on geography and genetics
I get way less White Mold , and chances of Bud Rot are greatly reduced where I am. Im not talking totally stripping leaves just about a third to open plant up to increased airflow.
 

pute

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Good article. However I prune the suckers at the bottom of the plant....both flowers and fan leaves. The lower flowers aren't worth messing with and suck energy from the top. As far as fan leaves go I prune so no leaves touch each other. I am in a high desert so the humidity is low but in a tent mold and PM is an issue.

Like Big I have done a side by side with little difference in yield. To each his own.
 

RosterMan

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Good article. However I prune the suckers at the bottom of the plant....both flowers and fan leaves. The lower flowers aren't worth messing with and suck energy from the top. As far as fan leaves go I prune so no leaves touch each other. I am in a high desert so the humidity is low but in a tent mold and PM is an issue.

Like Big I have done a side by side with little difference in yield. To each his own.
Lollipop them LOL Me too
 

pute

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I trim quite a bit. I'm growing buds to smoke not leaves.😁
I think the thinking on this has changed recently. I remember a thread in advanced growing techniques where a guy trimmed all fan leaves except the top leaves. If I remember that thread was on the farm. Personally I think that is a bit to much.
 

WeedHopper

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Yep,,I remember a guy from Jamaica that trimmed his up in flower and didn't leave anything but small leaves and sugar leaves. He had huge colas.
He said that those small leaves,, sugar leaves,,and buds could get all the energy they needed from the light.
And ya couldn't call him a liar because he had proof with his grow journals.
 

oldfogey8

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Good article. However I prune the suckers at the bottom of the plant....both flowers and fan leaves. The lower flowers aren't worth messing with and suck energy from the top. As far as fan leaves go I prune so no leaves touch each other. I am in a high desert so the humidity is low but in a tent mold and PM is an issue.

Like Big I have done a side by side with little difference in yield. To each his own.
I actually did more stripping of leaves on my resident president plant than I normally do. Stripped off everything about half way up from the bottom. The growth is now concentrated in the buds I would smoke(had these plants not been sacrificed to pollination gods) and the branches with buds on them are filling in nicely. I will do this on my future grows as it seems to be working well.
 

Hippie420

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In my indoor hydro SCROG's, I wait 'til the screen fills up and I'm tired of tucking the heads down, then a few weeks after I let the tops come up, I cut everything below the screen off.
Outdoors, I only cut the dead or dying leaves and let nature take its course.
 

bigsur51

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In my indoor hydro SCROG's, I wait 'til the screen fills up and I'm tired of tucking the heads down, then a few weeks after I let the tops come up, I cut everything below the screen off.
Outdoors, I only cut the dead or dying leaves and let nature take its course.


yep yep , different strokes for different folks


on my outdoor , like you , I like to let nature take its course , just set the plant free and see what she turns into

just like out in the wild….totally natural ……I believe it is under these conditions that one can experience the full essence and expression of the Plant
 

boo

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Due to the amount of humidity I have to deal with on a regular basis I usually strip most of the fan leaves on the top half so I have better circulation and I Lali pop the bottom for the same reason. Inversion I have three large fans moving air along with the air conditioning and I still have to deal with mold issues. It gets quite frustrating defined one of your nicest plants with mold on his leaves. It’s something I have to deal with living in the climate I do
 

Betrion

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I personally don't cut many leaves from the plant, but there always comes a stage when it is inevitable to cut some leaves so that the flowers get light. I am currently in a situation where the leaves bother me and I regret cutting them... It seems to me that the auto strains experience much more stress than the regular ones.

This is the current situation in the box, a picture from today. IMG_20220928_180149.jpg IMG_20220928_180156.jpg IMG_20220928_180159.jpg IMG_20220928_180203.jpg
 

joeb631a

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yep yep , different strokes for different folks


on my outdoor , like you , I like to let nature take its course , just set the plant free and see what she turns into

just like out in the wild….totally natural ……I believe it is under these conditions that one can experience the full essence and expression of the Plant
that was romantic .......
 

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