Growing Consensus Synopsis Paper
Should Fan Leaves be Trimmed?
There are a number of theories why fan leaves should or should not be removed. The purpose of this paper is to analyze cannabis cultivation techniques that advocate for and against fan leaf removal. A summary of each theory is presented, followed by a review of fan leaf function. The different theories advocating for and against the removal of fan leaves are then discussed in the context of fan leaf function and cultivation techniques.


THEORIES WHY TO TRIM FAN LEAVES
Increase Lower Bud Development
The fan leaves shade lower buds and that these buds do not develop to there full potential because of a reduction in lighting intensity due to shading from upper fan leaves.

To conserve energy for upper bud development
Trimming fan leaves and lower, shaded branches focuses the plant’s development on main top buds (Che Bleu, 03.13.2002). A plant wastes precious energy several ways. A tall plant needs to use energy to build extra stem, and then use extra energy to move water up higher, this is why I believe "scrog" methods are productive. An untrimmed bushy plant causes the plant to expend energy to build elaborate branches and leaves, and then has to use excess energy to supply all these structures. Careful trimming to remove unnecessary branches (which wont produce nice buds) and unproductive suckers will leave more energy for a larger yield. Suckers do exactly as their name suggests, they suck needless energy from the plant which can be put to better use, towards yield (Leaf, 03.13.2002).

Reduce the Stretch
If fan leaves are trimmed during the early flowering stage, the stretch is reduced (Che Bleu, 03.13.2002). Reducing the stretch might be advantageous in certain cultivation conditions.

Speeding Up The Flushing Process
Remove some of the fan leaves 14 days before harvest. It helps speed up the flushing process and or makes flushing unnecessary (Homemadepot, 03.13.2002).

Reduce The Chance of Mould
Removal of dead fan leaves is necessary to reduce the risk of mould. Failing to "clear the airway" can lead to development of mould in the "crowded" areas of the plant (Jeast, 03.13.2002).

Scrog growers may also reduce the chance of mould by removing fan leaves due to reduce the level of transpiration. This is because many scrog grows are in a confined space where humidity is a serious problem (DoctorDangerous, 09.04.2002). However with better ventilation it may be necessary to avoid the mould problem (Nietzsche, 09.04.2002).

Increase root development on Clones
Fan leaves on clones should have their blades cut in half, to make the clone grow slowly while a root system develops (Weezil, 03.12.2002).

HOW DO FAN LEAVES FUNCTION
The large fan leaves have a definite function in the growth and development of cannabis. Large leaves serve as photosynthetic factories for the production of sugars and other necessary growth substances. Most cannabis plants begin to lose their larger leaves when they enter the flowering stage and this trend continues on until senescence (death of the plant).

Fan leaves account for the greatest area for the reception of photons on a plant, thus they account for the majority of photosynthesis which occurs within a plant. Cells in the plant's leaves, called chloroplasts, contain a green pigment called chlorophyll which interacts with sunlight to split the water in the plant into its basic components. Leaves only absorb about 15% of the solar energy that hits them, the other 85% passes through-- but they reflect all the green light, which means it looks darker below the leaf to a human than it does to the plant because our eyes are most sensitive to the green spectrum (Shipperke, 03.15.2002).

Photosynthesis occurs in all green parts of plants. The process has two stages, the light reactions and the Calvin cycle, that convert water and carbon dioxide into sugar and oxygen. These sugars are later used to power all the processes in the plant, including the synthesis of THC and other cannabinoids (Shipperke, 04.02.2002; Ca, 03.13.2002). Fan leaves possess the greatest number of stomata, which are small pores or valves on the underside of the leaf which water vapor and carbon dioxide diffuse during transpiration and photosynthesis (carbon fixation). Carbon dioxide first enters the leaf through the stomata and combines with the stored energy in the chloroplasts through a chemical reaction (the Calvin cycle) to produce a simple sugar. This sugar is unloaded into the tissues and transported through tubes in the leaf to supply the synthesized food to other plant parts such as growing or respiring tissues like young leaves, roots, and flowers of the plant. meristems (UK Tricky Knome, 03.14.2002).

Removal of fan leaves will not only slow growth, but it will also hinder the plants ability to rid itself of toxic gases, and also hinder the regulation of the plants temperature via stomata. Changes in the plants chemical metabolism caused by fan leave removal causes the plant to work overtime to rid ‘toxins’ with less leaves, as a result the pant may allocate more growth hormones into growing more leaves to make up for what has been lost(Equator, 03.15.2002). Removing large amounts of fan leaves may also interfere with the metabolic balance of the plant. Leaf removal may also cause sex reversal resulting from a metabolic imbalance.

There is a relationship regarding the amount of carbohydrates a leaf produces and CO2 intake relative to outside forces. When you have a situation whereby the leaf is no longer productive for the plant for whatever reason that may be - low light, old age, disease, insect attack etc, the plant will discard it. (Thunderbunny as citied, by Nietzsche, 03.13.2002.

Plants have two different kinds of vessels in their stems to move stuff around, xylem and phloem. Xylem runs from the roots up the stem carrying water and nutrients. Phloem runs both up and down to move sugars hormones, proteins, etc but mostly sugars. Each part of the plant can be either a sugar source or a sugar sink (Shipperke, 03.15.2002). Phloem moves from sources (areas of supply) to sinks (areas of metabolism or storage). Granted that the flowers can produce some photosynthate, but they are no where near as effective as fan leaves (resin glands significantly reduce light to the tissue they are found on). Flowers are sink tissues, leaves are source tissues. Sinks do not produce enough photosynthate, and are importers. Sources give photosynthate to sinks in closest proximity. Upper leaves bring sucrose to shoot apical meristem and young leaves while lower leaves bring goodies to roots (UK Tricky Knome, 03.17.2002). Remove the source and the sink will be affected (Diels Alder, 03.15.2002).

The leaves at the top of a plant tend to supply the top growing shoots. The leaves at the bottom of the plant tend to supply the roots. The middle leaves can go either way as the demand changes. During flowering and fruiting, only the very bottom leaves supply the roots and the rest of the leaves try to get as much energy as possible to the flowers of fruits. For this reason, the more leaves are unshaded and in good light, the more chance the plant has of creating extra storage of energy that will ultimately go into yield (Leaf, 03.13.2002). However Jeast (03.13.02) believes that the rich green leaves emerging from the bud are a sufficient energy source of solar energy for the plant's floral development. Therefore the old fan leaves are once again rendered useless and only drain energy from the developing part of the plant (Jeast, 03.13.02).

Do you know if buds are formed when the light hits the bud? or is it when it hits the leaves and then transfers the sugars too the bud?

I know with tomatoes you clip the leaves to expose the fruit to the sun. I believe people tuck fan leaves on MJ to expose their buds to the light... but I haven't done this with MJ, just tomatoes.

I'm not seeing much consensus here just differing opinions, but will look forward to part 2.

I have heard that removing the large fan leaves a week or 2 before harvest can help ripen the lower buds, as the light is allowed to penetrate, but then again it's a well documented fact that light degrades THC.

As I see it; the plant stores energy during the vegetative phase (in it's leaves) and draws upon that energy reserve during flowering. Personally I try to leave as many healthy large fan leaves as possible, since they are the plants energy factory, and energy storage facility.

THEORIES WHY TO TRIM FAN LEAVES
Increase Lower Bud Development
The fan leaves shade lower buds and that these buds do not develop to there full potential because of a reduction in lighting intensity due to shading from upper fan leaves.

Makes sense to me

To conserve energy for upper bud development
Trimming fan leaves and lower, shaded branches focuses the plant’s development on main top buds (Che Bleu, 03.13.2002). A plant wastes precious energy several ways. A tall plant needs to use energy to build extra stem, and then use extra energy to move water up higher, this is why I believe "scrog" methods are productive. An untrimmed bushy plant causes the plant to expend energy to build elaborate branches and leaves, and then has to use excess energy to supply all these structures. Careful trimming to remove unnecessary branches (which wont produce nice buds) and unproductive suckers will leave more energy for a larger yield. Suckers do exactly as their name suggests, they suck needless energy from the plant which can be put to better use, towards yield (Leaf, 03.13.2002).

I cannot agree with the above statement, because fan leaves take-in, and store, more energy than they use.

Reduce the Stretch
If fan leaves are trimmed during the early flowering stage, the stretch is reduced (Che Bleu, 03.13.2002). Reducing the stretch might be advantageous in certain cultivation conditions.

Stretch is reduced? Not likely, because the more energy the plant receives the tighter the nodes. A plant with no leaves would stretch to find light.

Speeding Up The Flushing Process
Remove some of the fan leaves 14 days before harvest. It helps speed up the flushing process and or makes flushing unnecessary (Homemadepot, 03.13.2002).

I cannot agree with this either; flushing is necessary, and more leaves means more plant respiration, and in turn better water flow.

Reduce The Chance of Mould
Removal of dead fan leaves is necessary to reduce the risk of mould. Failing to "clear the airway" can lead to development of mould in the "crowded" areas of the plant (Jeast, 03.13.2002).

All dead growth needs to be removed, but I thought we were concerned with healthy fan leaves here.

Scrog growers may also reduce the chance of mould by removing fan leaves due to reduce the level of transpiration. This is because many scrog grows are in a confined space where humidity is a serious problem (DoctorDangerous, 09.04.2002). However with better ventilation it may be necessary to avoid the mould problem (Nietzsche, 09.04.2002).

Of course good air circulation is required below the scrog, but also by removing growth below the scrog, energy is focused above the scrog. Same theory as lolipopping

Increase root development on Clones
Fan leaves on clones should have their blades cut in half, to make the clone grow slowly while a root system develops (Weezil, 03.12.2002).

Yes, a leafy plant without roots can't support itself. This is why the vegetative growth is reduced.

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"If a law is unjust, a man is not only right to disobey it, he is obligated to do so." - Thomas Jefferson my grow

Hey JSchrroe, I believe it's both. Buds need strong light to ripen - just as many fruits do - but they leave energy is also drained. Leaves are supposed to turn yellow in the fall, but it's good practice to remove sick leaves. One they turn yellow I remove them.

__________________
"If a law is unjust, a man is not only right to disobey it, he is obligated to do so." - Thomas Jefferson my grow

buds do not collect light, leaves do. then the leaves feed the buds.

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ding ding ding ding ding

This statement made more sense than the original post, thanks fdd2blk!

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If leaves feed the bud why do the buds close to the light grow more and why does evry ones say to move leaves to the side to allow more light with bud? I don't know either way, I'm just a noob lol

the buds closer to the light grow more because their leaves are closer to the light.

they say that because for some reason they think they are smarter than millions of years of evolution.

stupid nature, put all these dumb leaves in the way.

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i'm the guy i've always wanted to be