The science behind defoliation?

No, you typically would -not- want to defoliate an already stressed plant (because you're adding a potential stressor on top of already existing stress.)
It mainly improves light distribution, airflow, and uniformity (this is the basic core concept of defoliation for cannabis.)
I'm still not clear if significant defoliation should be done to address a problem/stress (overly dense leaves causing poor ventilation and/or light penetration); or should be done particularly to healthy thriving plants to manage canopies.

What about growers who simply always do schwazzing, lollypopping and/or other very radical leaf removal? On AFN this is often done to exemplary thriving plants having good canopies, with way more defoliation than needed to address ventilation/light problems. Some remove all leaves with any stem multiple times during their grows. There are many examples on AFN of master growers achieving great success with such grows (e.g., 420 Method). Is this from skill/experience, green thumb/luck or is there supporting "science?"
 
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this has some referneces that might be useful: https://www.sciencedirectt.com/science/article/pii/S0926669025014645

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Concurrently, growers often prune, or mechanically damage, their plants (Danziger and Bernstein, 2021a). Mechanical damage to plant tissues has been shown to induce wounding responses akin to the herbivory response wherein the synthesis of secondary metabolites is increased (Ali et al., 2024). This can alter source-sink relationships, particularly the partitioning of carbohydrates (Verdonk et al., 2023), which can influence biomass allocation (Nie et al., 2021, Nie et al., 2023). When applied to C. sativa, pruning can take many forms (e.g., topping, lollipopping, defoliation etc.). While definitions do not appear to be uniform between studies, all approaches aim to increase flower yield and/or cannabinoid concentrations by affecting biomass partitioning and stimulating secondary metabolite synthesis, respectively.
Topping, lollipopping, and defoliation have distinct modes of action affecting cannabis growth and yield. By removing the shoot apical meristem, ‘topping’ encourages the growth of lateral branches due to relaxed apical dominance, thus achieving greater flower mass across the canopy (Folina et al., 2020, Crispim Massuela et al., 2022). This method can be paired with the ‘Screen of Green’ cultivation method, whereby fewer plants with highly branched canopies are maintained (Arora and Yun, 2023). ‘Lollipopping’ involves removing non-productive growth low in the canopy that is thought to have low flower mass or low cannabinoid yield, thereby directing carbon allocation towards floral production (Crispim Massuela et al., 2022). Indeed, it has been shown that the concentrations of most cannabinoids is higher in inflorescences closer to the apical meristem, and self-shaded branches lower in the canopy produce less floral biomass and have reduced cannabinoid content (Bernstein et al., 2019, Crispim Massuela et al., 2022, Stack et al., 2023). Finally, defoliation involves removing fan leaves (large palmately compound leaves that grow directly from the main stem and side branches, often made up of five to nine leaflets) from both the main stem and side branches to achieve an open canopy structure that is thought to allow better airflow (which helps mitigate disease risk) and light penetration to flowering sites. Light intensity (LI) correlates with floral biomass in cannabis (Holweg et al., 2024), so increasing the available photosynthetically active radiation at all flowering sites can theoretically increase dry floral biomass.
Defoliation is perhaps the most labour- and time-intensive of the described pruning methods as it involves carefully removing fan leaves across the entire plant canopy. Danziger and Berstein (2021a,b) show that defoliation increases the concentration and uniformity of certain cannabinoids across the canopy. However, cannabinoid yield was not increased by defoliation for all cultivars because dry flower weight sometimes decreased (Danziger and Bernstein, 2021a, Danziger and Bernstein, 2021b). The relatively low harvest indexes reported for each of their treatments may have come about due to low canopy LI. Further, Sandoval et al. (2024) show that damage to field-grown hemp with a flail (which they term ‘defoliation’) increases CBD, cannabidiolic acid (CBDA), cannabidivarinic acid (CBDVA), cannabigerol (CBG), Δ9-THC), tetrahydrocannabinolic acid (THCA), tetrahydrocannabivarin (THCV), and tetrahydrocannabivarinic acid (THCVA) concentration if performed during the early flowering stage. Toth et al. (2021), on the other hand, found that mechanical wounding of field-grown hemp did not cause significant changes to the cannabinoid potency of the flowers. Beyond this, there is a lack of research into the effects of proper defoliation on C. sativa growth and yield in indoor settings."
Bloody hell, I did hit the points button. This is the second time! Have yerself some pseudo points then, the thought was there. :pighug:
 
FWIW, I remove limited #s of leaves in order to open air flow, but not for other reasons. So far, I have never had even a hint of bud rot on my indoor grows, but, OTOH, I have always kept my canopies flatter with topping, and open with trimming strategic fan leaves so I do not really know for sure if trimming was necessary, or the results would have been the same without it. I get decent yield, but so far, never a pound.

The coming grow, however... If my seeds arrive, I will be doing some Dutch Passion girls that have the potential. :cheers:
 
I happened to find "Heavyweight autoflower yields: from myth to reality," at the Dutch Passion Web site (https://dutch-passion.com/en/blog/heavyweight-autoflower-yields-from-myth-to-reality-n1234), about the 420 Method. The first sentences are:
'
"Recent advancements in autoflower seed genetics and cultivation practices have significantly enhanced the performance potential of these plants. When paired with refined hydroponic techniques, some growers have reported achieving dry yields of approximately 1kg under controlled conditions.
One approach involves multiple rounds of intensive defoliation (‘schwazzing’) during the life cycle, which may extend the plant's development period from an average of 75 days to approximately 110–120 days. This extended timeframe can support increased floral development and overall plant mass."


So radical defoliation "may" extend the plant's lifetime with continued growth and development in that added time. Seems similar to extending the veg period with photoperiods? This could a good reason to radically defoliate - get more out of each plant, maybe even better quality. But 110-120 days is 47%-60% more time vs. the cited average 75 days to harvest (and schwazzing takes a lot of manual effort/time). What does schwazzing provide that makes this ~50% longer time to harvest and added work worthwhile? Perhaps @Antonio_DutchPassion, the author of this article(?), can comment.

Is this schwazzing lifetime extension established 'fact,' backed by "science"/studies, consensus among expert growers, or just anecdotal grower reports? What are its benefits vs. well-executed mainstream growing - improved potency, high, yield (more per sq. ft., not per plant), bag appeal, etc.?
 
This might help.


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Is there any additional information from this study/article? Lab results are reported, but what about the high from each set of buds? And how many additional man-hours were devoted to the schwazzing tent?

Have any large commercial/legal growers published/presented about benefits (or not) from radical defoliation, perhaps comparison grows at larger scale?
 
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Yeah I understand where you coming from. For the record btw, I'm not the author of that blog, that's Tony, our main guy writing all the blogs/data for Dutch Passion. This particular blog and info was based upon things we have seen with @420autoflower SCROG method, growing on hydro and a direct effect for putting up such a blog. What he (and we as well) have seen so far is that when you either grow plants in massive containers, or when you grow them in hydro and do extreme defolation/schwazzing methods, it seems autoflowers are kind of 'stressed' and wait a bit longer with going into flowering and first go into a sort of repair-mode.

However, yes this is still a bit bro-science and not yet backed by doing this on a large scale, I think simply because autoflowers are not often used by professional growers to produce bud, simply because of the pheno differences (clones are always best to standardized bud of the same quality). Ofc. the flowering time also has to do with the genotype (and phenotype) of the seed, which can vary greatly ofc.

With the example 420 has given here above I'm not sure if it proves anything tbh, merely by the fact that doing this with autoflowers is never a fair comparison.. because every plants comes from a seed. To do a proper side by side grow and test 2 two different techniques you would need clones, thus photoperiods in this case. And otherwise do it with one (homegenous) autoflower strain on a farily large scale, set up a test with 100 vs 100 plants and take data to make a good comparison.
 
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