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I found this through a google search, the author makes a good point that I haven't considered.
It takes energy to keep a leaf alive.
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"That's where defoliation comes in; by removing some of this excess foliage, not only do you free up some of your plant's energy (by reducing the amount of foliage it needs to keep alive), but you help your plant make better use of its
limited light source. "
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"Does defoliation increase yields?
Pruning, or defoliation, is a technique that keeps your cannabis plants healthy and growing properly. By removing small amounts of foliage during various phases of the life cycle,
growers can increase a crop's yield and potency by allowing light to hit bud-producing nodes more directly."
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"How can this be? Why would the plant make leaves if it doesn’t need them?
Outdoors, cannabis plants need extra leaves to store nutrients and create an extra wall of defense in case the plant gets attacked by pests or otherwise loses all its leaves. But indoors there should be no
pests, and you are there to give your plants the exact
nutrients it wants at the exact right time. This makes holding onto leaves a lot less useful for the plant, especially some plants which get extremely bushy without defoliation."
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Cannabis isn’t the only plant that benefits from defoliation
To those naysayers who claim defoliation can NEVER work, I think it’s important to point out that cannabis isn’t the only plant that rewards growers with bigger yields and higher quality from defoliation. Some commercial crops, such as cotton, need to be defoliated during their grow to produce the best yields and quality of cotton. In fact, even after 40 years of intense study on cotton defoliation, there is still controversy and
ongoing research by commercial crop producers to further pinpoint the exact time and way to defoliate cotton plants in the field to produce the best results."
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"Proponents of defoliation generally cite higher yields as a benefit of defoliation, and it is this particular claim that is most in contention.
Opponents often invoke reduced photosynthetic activity as their reason against defoliation. The argument goes: more light, more leaves, more energy, more nutrient reserves, more yield.
Opponents are correct in their belief that photosynthetic activity is generally reduced by medium to heavy defoliation. Experiments involving defoliation and its effect on yield in many diverse plants have shown a consistent, causal link between defoliation and reduced yield in field-grown plants (outdoors.) This decrease is attributed to plant stress and decreased photosynthetic activity.
An exception in which yields increase is when the leaves removed have begun to senesce and have become sinks on the plant, rather than sources.
Typically, these older, larger fan leaves have lost efficiency with age. Opponents of defoliation often use the solar panel analogy. More and bigger solar panels mean more food for the plant. However, just as solar panels from 10 years ago are less efficient than those produced more recently, leaves also lose efficiency as they age. Leaves can begin to require more energy to stay alive than they produce. At this point, they are energy sinks, just as buds are. Unfortunately, buds as sinks produce a desired product; leaves do not. So at this point for the leaf, it is ALWAYS beneficial to remove them."
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Beyond Yield :
Release of Volatiles as a Defense against Herbivory
"Terpenes are present in varying degrees in many healthy plants. However, when plants are damaged or defoliated through herbivory, particularly from insects and mites, the levels of terpenes and other volatiles are substantially increased in response to the damage.
This increase in volatile production, including terpenes, is most often used as a signal to repel pest insects, or more commonly, to attract the enemies of pest insects.
This effect appears to be systemic, meaning; infestation on an individual branch will elicit terpene production in distal, undamaged branches. "
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