I'll never forget the first time I saw a plant completely defoliated by human hands, it wasn't a pretty site and it reminded me of my childhood days of plucking chickens. In my later childhood I witnessed the difference between naturally grown plants and those disturbed by rumnant types of foraging animals. The plants that were stripped of leaves never developed and always lagged behind the others.
In no way am I against pruning or some removal of excessive shade leaf while trimming sucker branches better known as "lolipoping" admist other growers. I do it with some plants and with some plants I'd be a fool to trim lowers. Same with removal of the shade leafs, it definitely depends upon the overall plants size and the sheer amount of leaf to stem ratio. Many of today's hybrids and a good amount of the Narrow Leaf Drug types produce a very limited amount of foilage in comparison with the Broad Leafed Types. Diesels and OG Kush would be examples of plants that often have very long internode spacing with a much lower ratio of Leaf-Stem and defoliated these are often robbed almost completely of their photosynthesis production upon removal of their leaf through complete defoliation.
I suppose I'll close my comments with one last thought, and this being "moderation within all" for I believe it's the key to success and actually gaining an increased yield in both weight and potential.
Good references @drphoton thanks. I have a deep interest in cannabis botany. Here's my takeaways from a bit of reading them
In Taiz Physiology, he defines these
-- "The light compensation point is reached when photosynthetic CO2 assimilation equals the amount of CO2 evolved by respiration. "
-- "Sinks include any nonphotosynthetic organs of the plant and organs that do not produce enough photosynthetic products to support their own growth or storage needs "
To me that says a leaf without enough light is a sink, by definition. Perhaps I am missing something.
He does not define (require) a sink as an endpoint in translocation, but he mentions (without detail)
"the transition from import to export is to some extent reversible".
That whole section is about the sink to source transition, which is why it is called "The transition of a leaf from sink to source is gradual". Where it is explained how the transition occurs during the initial juvenile phase and is completed by its matured stage. The transition is accompanied by a set of anatomical and functional changes that are permanent, where import cessation is independent of the leaves developmental status. Meaning that even if the leaf cannot provide any sufficient quantity of photosynthate for export or for its own respiration, the leaves will still stop any phloem unloading from occurring once a certain developmental stage is reached . This is referenced by the studies done on tobacco that compared green leaves with albino leaves (lack of chlorophyll), showing that phloem import stops at the same developmental status, regardless of the photosynthetic capacity of the leaf. So even though the albino leaves were not able to provide anything to photosynthate production and phloem loading, or for its own needs. The leaf was still removed of its access to phloem imports (acting like a sink). And left to the natural processes of PCD and senescence.
So when the book mentions that "sinks include any nonphotosynthetic organs of the plant and organs that do not produce enough photosynthetic products to support their own growth or storage needs". It is only applicable to organs which poses the anatomical capabilities to support phloem unloading.
In reference to the part about the "transition is to some extent reversible", you must have gotten that from a much older version of the book. Which now does not contain that segment and is entirely removed. Probably to avoid confusion of the intentions of that particulate section. But to answer it, this only occurs is certain species that retain the symplastic route for phloem unloading, for example with the coleus that has variegated leaves with both green and albino segments. Where the albino regions of the leaf act as sinks towards the green areas on the same leaf structure (not independent leaves). When the green segments are removed, the albino regions can work through the still remaining symplastic pathways to unload sugars from other mature leaves. Again, this is rare and does not follow the typical process of the sink-source transition in most plants, which is why it was likely removed with the most recent additions of the book.
The articles were good, but the "Age effects on photosynthesis” was most excellent. As I read it, its a pretty good case in favor of deleafing during the first half of the plant life.
I've read older leaves lose efficiency by I didn't recall reading how dramatic it is:
"the photosynthetic capacity declined logarithmically to values of 50% and 25% of the maximum 9 and 25 days later, respectively "
And they mention
"sink effects that can correlate with decreases in photosynthetic productivity. "
Yes the age aspect of the photosynthetic capacity of leaves is a major contributing factor for senescing activation in cannabis, which is connected to the entire whole plant senescing process with annual reproduction species. This aging aspect has already been brought up here before and has no relevance due to the nature of the geometry of new and old leaves, where the youngest leaves are almost always situated at the top of the canopy, where it consumes the majority of the light captured.
The mentioned "sink effects that can correlate with decreases in photosynthetic productivity" refers to the impact that sink demand and strength has on the photosynthetic production that leaves have, as there is a relationship between sink strength and the photosynthetic output by leaves. And its contribution towards the senescing process, as the photosynthetic characteristics are correlated with how the senescing process occurs. Again, not a relevant factor.
About canopy management, the problem is worse in a crowded canopy
"as canopies become denser, crown-to-crown competition among neighboring plants further increases the spatial and temporal crown light interception asymmetry [2,3]. These heterogeneity effects on the within-canopy light environment can accelerate leaf aging and subsequently decrease photosynthetic performance "
They saw such promise in deleafing that they stated "removal of older leaves throughout the crop cycle may enhance canopy CO2 uptake and ultimately crop yield. "
And they are working the development of a model and further research into the topic. That will be an interesting paper.
They are referring to the partitioning effects of co2 assimilation, which is most applicable to hemp cultivation where plant management is not the same as typical cannabis cultivation. We use growing environments that replace air sufficiently enough to provide constant co2 concentrations that does not degrade due to assimilation and co2 diffusion limitations. The only situation this would occur with indoor cultivation, is when the cultivator has insufficiently configured the growing system to maintain adequate environmental variables.
If you had read further into the "making sense of senescence", you would have found the answer around the light compensation issue. Where it mentions the factor that triggers senescence and why leaves do not and have not been observed to act as sinks after the sink-source transition.
"In one general model of what triggers the senescence program, leaf senescence is initiated when the photosynthetic rate drops below a certain threshold. That threshold
may be at or near the compensation point at which the leaf no longer contributes fixed carbon to the rest of the plant"
The senescence process is a well structured and highly coordinated programmed cell death system. It is not a degenerative phase as a result of age and then simply dies out, it is more correctly defined as a recycling process. Where resources left over from the leaf, such as and especially nitrogen that is harvested primarily from chloroplasts. And is reused and becomes a more efficient source of nitrogen that does not need further energy to assimilate ( like with N absorbed by roots).
It is no coincidence that it has been observed that leaves will begin the senescence when a certain photosynthetic threshold has been reached, as it would be in the best interest of the plant to initiate it before it no longer has enough capacity to undergo this recycling process. As any later would limit its ability to effectively recycle any remaining resources in the leaf.
Again, the compensation point in most plants is very very low, with the majority landing somewhere between 1 and 50umols. I have personally tested cannabis by using low light therapy, where it has shown that the light compensation point of cannabis is in the single digits, somewhere below 10umols.
My time is limited to these responses, so please dont be offended if i do not respond any further. If you are genuinely willing to learn, i highly suggest picking up a hard copy of the latest book on plant physiology by taiz. And there are further books that extend on this such as the biochemistry of photosynthesis, senescing, photoperiodism etc that are available under our recommend books section. Which provide a more deeper aspect of different parts of plant related science.
All the best.
Always appreciate your insight and opinions.
Incidentally i had read the paper on senescence and the textbook section; and had bookmarked the same section cited above, since we were discussing pre senescence and carbon fixing, i didnt mention it.
Whew..i gotta say this is good shit.. But man its hard to comprehend for me. Ill read it a few more times first...but I do have a few questions lol thanks for takin time to put all this out here growmies.
I have to disagree with a common notion that we are facing nowadays when it comes to cannabis. Of course, I respect and admire the benefits for so many cancer patients and chronic disease-affected people. However, we have to look at the other side of the coin regarding excessive usage. It's still a very addictive substance similar to Xanax. The worst thing is when people combine marijuana and Xanax and smoke it. One of the main issues that my brother destroyed his life, and I had to find a rehabilitation center to deal with it. If you have someone close to you but face is such an issue, it's better to show them this article https://fherehab.com/learning/smoking-xanax/ where it is clearly explained how devastating it can be for your health to do such a thing!
I am a newer grower, but I did notice that my flowering plants that were getting hit with the most wind grew the biggest, weather that is because of the constant high level of CO2 that it receives or if it is a hormonal response, I don't know, but I am considering to remove excess under growth and add more floor fans to ventilate under the canopy to hopefully get more filled out and triched out lower buds. This only seemed to make sense to me because these larger buds I have are the furthest away from the light. My set up is in a 4x4 tent with tower fans hung in opposite corners. the 2 corners with tower fans have the bigger buds, where the corners with out the fans are noticeably smaller. The sample size is as small as it gets but I was wondering what you folks might think of wind inducing bud and trichome growth. Also, thinking about what would nature want to do to maximize reproduction, making sticky pollen catchers where ever there is airflow makes logical sense.
Cheers!
Remember — don't do too much trimming at once especially in flower, the stress could cause the plants to herm. I usually start around week 3 or 4 then will prune some and give it a week before pruning again. Twice is usually enough, but all strains grow differently.
It is perfectly safe to defoliate your cannabis plants and in fact, is encouraged as part of your standard plant care routine. It can be a nerve-racking experience the first time you cut anything off your babies but if you can face this fear, you may just end up with more bud! Let's go through the steps to defoliate your plant safely.
