Defoliation, a scientific approach...

[manti]

Hello rollitup community!

I was just doing some research on defoliation and got no reliable answers from the growers forums as everyone is following either the "pro" side or the "contra" side. The thing is, that very few scientific facts from current studies is involved in those discussions.

I would very much love to get the people to the point at that they start to compare scientific evidence and not their personal attitude. So it would be great to start a scientific discussion here, where the facts count more than opinions. If you have any additions, more scientific literature, conducted comparable experiments by your own or just want to add some newer scientific sources please take part in this discussion. I hope this doesn't become "yet another defoliating thread" but more like a base for real information exchange. Please notice, that when discussing the effects of defoliation the location of the grow (indoor/outdoor), the type of light source and the training of the plants (tree like/flat canopy) are very important factor as they alter the light availability, light penetration, and light distribution.

There have been done some experiments on cannabis, but sadly most of them lack the most important things:

1) A control group which isn't defoliated
2) A large enough sample size, should be ideally 30 plants in each group
3) Same environmental influences for all plants (light, water, nutrients)
4) Genetically identical plants such as clones.

One of those experiments was documented by Keef Treez "The Defoliator", you can find his article at growweedeasy. Sadly there is no control group involved, but at the first glance it seems to work. However this were not the kind studies I was out for. I digged a little bit deeper and found some more or less recent scientific work focussing on the topic of defoliation and the effects. First of all it is important to notice that none of the studies was done with cannabis, in fact much of them are covering defoliation through grazing but I found a lot of other studies as well. I think there are a some similarities between all those different plants and cannabis, which can be helpful for a better understanding of the processes.

 

[manti]

So lets get to the literature work...

"The reduction in whole plant photosynthesis following defoliation is not necessarily proportional to leaf area or biomass removal because of associated modification in canopy microclimate, the unequal photosynthetic contributions of leaves
of various age and, in some cases, compensatory photosynthesis. For example, when mature, previously shaded leaves remain on the plant following defoliation, canopy photosynthesis is reduced to a greater extent than the proportion of leaf area removed because of the low photosynthetic capacity of the remaining leaves (Ludlow and Charles Edwards 1980, Gold and Caldwell 1989b). A large decrease in thephotosynthesis/transpiration ratio of the canopy (i.e., water use efficiency) is also associated with this pattern of plant defoliation (Caldwell et al. 1983, Gold and Caldwell 1989b). Conversely, if a high proportion of relatively young leaves remain on the plant following defoliation, the reduction in canopy photosynthesis is more directly related to amount of leaf area removed. Consequently, canopy measurements of photosynthesis are more strongly correlated with the potential for regrowth than are measurements of single leaf photosynthesis (Ludlow and Charles Edwards 1980, Parsons et al. 1983a, 1983b, King et al. 1984, 1988, Nowak and Caldwell 1984, Gold and Caldwell 1989b)."
...
"Rates of leaf and tiller growth on defoliated plants may occasionally exceed those of undefoliated plants and can increase the rate of canopy reestablishment. More rapid leaf expansion on defoliated plants than on undefoliated plants has been
observed in a number of species, including crested wheatgrass, tall fescue, Kyllinga nervosa , and kleingrass (Panicum
coloratum) (Wallace 1981, Wolf and Parrish 1982, Wallace et al. 1985, Gold and Caldwell 1989a). In crested wheatgrass, grazed tillers had higher relative growth rates than tillers of ungrazed plants when grazing occurred prior to internode elongation in the spring (Olson and Richards 1988c)."
...
"Defoliation may also increase leaf initiation by increasing irradiance on the remaining portions of the canopy thereby potentially increasing photosynthetic efficiency and increasing carbon availability for leaf replacement (e.g., Gold and Caldwell 1989b). An increase in leaf initiation rate with increasing irradiance (Anslow 1966) and leaf area per tiller (Grant et al. 1983) is well documented."

-- Briske, David D., and James H. Richards. "Plant responses to defoliation: a physiological, morphological and demographic evaluation." Wildland plants: physiological ecology and developmental morphology. Society for Range Management, Denver, CO (1995): 635-710.

"In the current study we observed substantial compensation in defoliated plants growing at low density, despite losing 75% of leaf area prior to the onset of flowering. Plant responses associated with compensation included (1) increased reproductive efficiency, which may in turn may have resulted from increased canopy light penetration and transient increases in leaf-level photosynthetic rates; (2) greater allocation to reproduction (RA); (3) changes in biomass allocation from roots to shoots; (4) lower leaf longevity, and (5) increased percent fruit set. Although some of these responses were also observed in defoliated plants grown at high density, the inability of high-density plants to compensate appeared to result from competition for light; these plants delayed reproduction and continued to produce new leaves late in the growing season after low-density, defoliated plants had shifted allocation of resources to reproduction."

-- Oecologia July 1997, Volume 111, Issue 2, pp 225-232 Defoliation of the annual herb Abutilon theophrasti: mechanisms underlying reproductive compensation

 

[manti]

"After defoliation, which removed all leaf tissue above the ligule of leaf 3, the rate of photosynthesis of the remaining two older leaves fell to 90–95 per cent of that of control leaves, but they exported more of their assimilated carbon to meristems elsewhere in the plant during the first 48 h after the defoliation. The level of export from the two older leaves began to decline when new leaf tissue regrew from the shoot apex, and fell below that of the control leaves 4 days after defoliation. The two older leaves supplied the assimilate used in the regrowth of new leaf tissue immediately after defoliation: previously they had exported most of their assimilate to root. There was no evidence that ‘reserves’ were mobilized to meet the needs of regrowth at leaf meristems or, indeed, of the growth in stem and root; current photosynthesis supplied sufficient assimilate to account for all observed growth. In general, the plants responded to defoliation with a rapid and marked re-allocation of assimilate from root to leaf meristems, with the result that root growth was severely retarded but new leaf tissue grew at 70–100 per cent of the rate observed in control plants."

-- Annals of Botany Volume 39 Issue 2 Pp. 297-31. Defoliation and Regrowth in the Graminaceous Plant: The Role of Current Assimilate.

"When the external nutrient supply was high, removal of the laminae of fully expanded leaves, which comprised about two-thirds of the total leaf area, did not reduce leaf expansion. When the nutrient status was low, these leaves were of primary importance, presumably because of their role as a source of labile nutrients."

-- Annals of Botany Volume 30 Issue 2 Pp. 173-184. Leaf Growth in Dactylis glomerate following Defoliation.

"Partial defoliation always induced rejuvenation in photosynthetic rate of remaining leaves. Young and middle-aged leaves rejuvenated to rates comparable to those of recently expanded leaves but old leaves only partially rejuvenated. Time after defoliation to attain peak rates increased as leaves aged; values were 5, 9 and 12 days for plants partially defoliated on days 16, 30 and 65 of regrowth respectively. Peak rates were maintained for only 3 or 4 days before declining. Rates of photorespiration and photosynthesis were closely coupled. Transpiration rates varied over time in a similar but more erratic pattern to net photosynthetic rates.
Changes in net photosynthetic rates associated with senescence, defoliation treatments and irradiance levels were largely attributable to changes in intracellular resistance to CO2 transfer. Intracellular resistances ranged from 2.6 to 30 s cm-1, constituting 67-95 % of the total resistance to photosynthesis. Stomatal resistance to CO2 diffusion remained low, 0.2 - 1.0 s cm-1, for all but very old leaves.
Partial defoliation followed by continual removal of new crown and stubble shoots induced very high net photosynthetic rates, c. 15 days later. Highest net photosynthetic rate was 238 ng CO2 cm-2 s-1."

-- Australian Journal of Plant Physiology 1(4) 561 - 578. Influence of Partial Defoliation on Photosynthesis, Photorespiration and Transpiration by Lucerne Leaves of Different Ages.


So it seems to be important which leaves you remove, if you do it correctly you can expect more "above the earth" growth afterwards. Interestingly older Leaves may be able to rejuvenate and take the role of the removed leaves. Nevertheless defoliation seems to slow down the root growth, because assimilates are reallocated to the new growth and not longer to the roots. This retardation lasts for the recovery time, until the plant has re established a new balance. Those are some basic things which will be mostly important in the vegetative state. Additionally it seems to be important how much nutrients are available for the plant to work with. If soil nutrient levels are low, defoliation hits the plant more.

 

[manti]

Let's move on to the "budding" facts...

"Floral development in emerging shoots of unrooted hardwood Chinese gooseberry (Actinidia chinensis Planch.) cuttings was enhanced by continuous defoliation, inhibited by total shading, and unaffected by tipping. Leaf production and growth, shoot elongation and thickening, and new bud development were similarly affected by such treatments. These effects were generally related to severity of treatment and length of time treatments were applied."

-- New Zealand Journal of Agricultural Research Volume 18, Issue 4, 1975. Effect of defoliation, shading, and tipping of shoots on flower bud development and vegetative growth of Chinese gooseberry (Actinidia chinensis Planch.).

"Three experiments were done in an open-sided glasshouse during the normal winter growing season. In experiment 1, swards of the Dwalganup strain which were severely defoliated, either after flower initiation or at early flowering, had 17% more flowers per unit ground area than uncut controls. Swards which were defoliated at both stages had 28% more flowers than the controls."

-- Australian Journal of Agricultural Research 23(3) 427 - 435. The effect of defoliation on flower production in subterranean clover (T. subterraneum L.).

"Swards of three strains of subterranean clover (Seaton Park, Yarloop, Midland B) were subjected to a range of defoliation treatments.
In all strains, cutting at weekly intervals at a height of 1.5–2 cm from 1 month after sowing until the onset of flowering led to a slight delay in flower initiation but the time of flowering was little affected. The rate of inflorescence production, however, was always increased, as was the total number of inflorescences produced by the end of flowering. In particular, seed yields were increased by at least 30% compared with uncut controls."

-- Australian Journal of Agricultural Research 29(4) 789 - 801. The effect of defoliation on inflorescence production, seed yield and hard-seededness in swards of subterranean clover.

"The effects of various defoliation treatments on flower initiation were studied in the strawberry var. Talisman, which is a facultative short-day plant, with particular reference to differences in the inductive capacity of leaves of differing maturity.
Plants from which all mature leaves had been removed to leave only two immature leaves flowered in longer photoperiods than intact controls, and conversely plants bearing only three fully mature and no immature leaves required a shorter photoperiod for flower initiation than intact plants.
Intact plants in constant darkness and totally defoliated plants in continuous light both initiated flowers, but intact plants in continuous light failed to flower.
It is submitted that these results provide evidence that the photoperiodic control of flowering in this plant operates through a flower inhibitor produced in the leaves.
They also show that although leaves of any maturity are able to inhibit flower initiation, under some conditions mature leaves are more inhibitory than immature, and that the inhibitory activity of any leaf decreases with decreasing photoperiod."

-- Annals of Botany Volume 24 Issue 4 Pp. 482-490. The Role of Leaves as Inhibitors of Flower Induction in Strawberry: With one Figure in the Text.

"Experiments were performed in order to prevent the abortion of the first inflorescence of tomatoes (Lycopersicon esculentum Mill.) grown in insufficient light conditions."
Defoliation experiments showed that there was a flowering-inhibition by young leaves. Removal of these young leaves, especially those which were produced just before inflorescence initiation, promoted flowering. It is assumed that defoliation acted by removing the primary sinks for assimilates.
Applying growth substances directly on the inflorescence stimulated the development of this inflorescence. Benzyladenine was active but a mixture of this cytokinin with gibberellic acid was the most effective. It is suggested that the promotive effect of benzyladenine was mainly by redirecting the flow of assimilates, while gibberellic acid would stimulate, specifically, the development of floral parts."

-- J.M. Kinet 1976. Effect of defoliation and growth substances on the development of the inflorescence in tomato.

"Defoliation of the panicle of Rumex crispus L. (curled dock) at anthesis had little effect on the number of seeds (nuts) produced but lead to a very severe reduction in total seed weight per panicle and in the size of individual seeds. In particular the proportion of larger seeds was reduced drastically. The seeds from defoliated plants germinated more rapidly and had less precise requirements for germination than those from untreated plants. They did not suffer any loss of viability. A microscopic examination of cross sections of seeds revealed that seeds from defoliated plants had thinner walls (investing structures). They also exhibited a higher absorptive capacity for water. This information provides an important basis for further studies on the biological control of this weedy species."

-- Canadian Journal of Botany, 1971, 49(7): 1123-1130, 10.1139/b71-162


As a conclusion from this sources it seems like defoliating -if done correctly- can increase the number of buds on the plant. This could be because of the change of the chemical balance in the plants, it seems like the leaves may contain certain phytohomones which inhibit budding. Moreover young shoots seem to act more as sinks, therefore taking vital energy away from the buds. Regarding the seeds it seems like defoliating reduces the seed weight, which isn't much of a surprise at least the growth of fruits takes a lot more energy than growing buds. Well I guess the fruits won't be of big interest for most of the people here.

 

[manti]

Looking at those studies I think that defoliation may especially produce decent results in indoor environments with low power lights as CFL or FT, however I saw some people talking about using it with HPS or MH as well.

I hope this one wasn't to long, but I wanted to cover at least the basics with literature sources. There is a lot of additional stuff out there which I left out.

Please leave a comment what you think and take part in the discussion.


Regards

Dave

 

[chuck estevez]

my conclusion,


MORE B.S. UNTIL someone UNBIASED does an actual side x side with different strains, WITH cannabis. That is all.

 

[manti]

my conclusion,


MORE B.S. UNTIL someone UNBIASED does an actual side x side with different strains, WITH cannabis. That is all.

Well I think specific parameters in plant physiology have developed very early, that's why you can compare different species on a biochemical basis. There are definitely a lot of things we can learn from studies on other plant species. But you are right in that point, that the results will still differ between species and even stains.

 

[chuck estevez]

Well I think specific parameters in plant physiology have developed very early, that's why you can compare different species on a biochemical basis. There are definitely a lot of things we can learn from studies on other plant species. But you are right in that point, that the results will still differ between species and even stains.

different plants use nutrients at different rates, only a few plants are similar to cannabis, NONE of those where even used, so, ALL that you posted is really just hearsay. SHIT, I would be happy to see one person from this site actually finish a side x side grow, but, they always seem to fall off before the experiment is finished. HMMMMM?

 

[Aeroknow]

my conclusion,


MORE B.S. UNTIL someone UNBIASED does an actual side x side with different strains, WITH cannabis. That is all.

Exactly

 

[manti]

my conclusion,


MORE B.S. UNTIL someone UNBIASED does an actual side x side with different strains, WITH cannabis. That is all.

Well I think specific parameters in plant physiology have developed very early, that's why you can compare different species on a biochemical basis. There are definitely a lot of things we can learn from studies on other plant species. But you are right in that point, that the results will still differ between species and even stains.

different plants use nutrients at different rates, only a few plants are similar to cannabis, NONE of those where even used, so, ALL that you posted is really just hearsay. SHIT, I would be happy to see one person from this site actually finish a side x side grow, but, they always seem to fall off before the experiment is finished. HMMMMM?

It isn't about nutrients, it is about distribution and use of phytohomones in this case, you can learn a lot about this by looking into arabidobsis which is mostly used as model plant and it has been prooven that you can transfer those knowledge to other plants. So it really doesn't matter for this question if it is a rosales or a solanum, it is more about plant biochemistry and regulatory mechanisms.

I am waiting for this side by side experiment as well. Some time ago someone (I think on this forum) said he wanted a test with a larger number of plants. Sadly that was his last post on this topic as I read that one... Is there really no one who has tried anything compareable that you know of?

 

[lilroach]

I agree with Chuck.....I've followed several attempts and side-by-side comparisons on here and for some unknown reason the threads just ends mid-way through with no conclusions.

Even when there's been good side-by-side comparisons for such things and nutrients, it rarely converts or convinces those on either side of the debate.

And then those threads end up being 50 pages of creative name-calling and drivel.

So I'll start: You (fill in the name of someone you disagree with) know nothing about (whatever subject is at hand) and I know much more than you! I think you're a total waste of skin and you're robbing all of us of the air your breath!

I guess we can end this thread now as I saved us a lot of time.

 

[chuck estevez]

you messed up, you used "you're" properly in YOUR analogy,lol

 

[manti]

I agree with Chuck.....I've followed several attempts and side-by-side comparisons on here and for some unknown reason the threads just ends mid-way through with no conclusions.

Even when there's been good side-by-side comparisons for such things and nutrients, it rarely converts or convinces those on either side of the debate.

And then those threads end up being 50 pages of creative name-calling and drivel.

So I'll start: You (fill in the name of someone you disagree with) know nothing about (whatever subject is at hand) and I know much more than you! I think you're a total waste of skin and you're robbing all of us of the air your breath!

I guess we can end this thread now as I saved us a lot of time.

Sadly this is the thing when it comes to this topic. The people tend to bash each other instead of collecting scientific evidence. But I don't see any argument against collecting scientific work on different species to look at the mechanics behind it, as this mechanics apply to cannabis as well. In the end it should be possible to identify the important factors in defoliation and put those factors into practice in an experiment.

 

[chuck estevez]

Sadly this is the thing when it comes to this topic. The people tend to bash each other instead of collecting scientific evidence. But I don't see any argument against collecting scientific work on different species to look at the mechanics behind it, as this mechanics apply to cannabis as well. In the end it should be possible to identify the important factors in defoliation and put those factors into practice in an experiment.

what OTHER plants are grown indoors under artificial lights, forced flowered, forced to go un pollinated and smoked when finished? Were any plants like that used in these scientific studies? Because in my world, if not, then they are not the same mechanics. My 2 cents

 

[manti]

what OTHER plants are grown indoors under artificial lights, forced flowered, forced to go un pollinated and smoked when finished? Were any plants like that used in these scientific studies? Because in my world, if not, then they are not the same mechanics. My 2 cents

Other plants form resins on trichomes as well, and there are a couple of plants which are studied for essential oil production from the leaves. There are some studies on the influence of defoliation on trichome development in Euphorbia spp. for example, other studies focus on the content of essential oils in the leaves of defoliated plants. I think there might be some clues about what degree of defoliation leads to which results and if the location of the removed phytomass matters...

Edit: You don't smoke your kitchen herbs of course, but you are after the same thing...

 

[lilroach]

Sadly this is the thing when it comes to this topic. The people tend to bash each other instead of collecting scientific evidence. But I don't see any argument against collecting scientific work on different species to look at the mechanics behind it, as this mechanics apply to cannabis as well. In the end it should be possible to identify the important factors in defoliation and put those factors into practice in an experiment.

Yeah....we'd all like to think we'd strive for more conclusive knowledge but after several years reading threads on here it appears there's more chest-thumping than intellectual research.

I honestly hope that this thread is different.

 

[manti]

Yeah....we'd all like to think we'd strive for more conclusive knowledge but after several years reading threads on here it appears there's more chest-thumping than intellectual research.

I honestly hope that this thread is different.

I am new to this forum so maybe I am a little bit naive about that, but I hope the best. There must be people out there, who are interested in scientific exchange... ... I hope... :-/

 

[skunkd0c]

how many leaves do i need to remove before it is classed as "defoliating" ?
i only have one plant growing at the moment but its going to be a big one
i was wondering how many leaves a big plant could have, i find it difficult to even estimate 100 200 500 1000 or more ?
i guess ill have to just count them all if i really want to know lol

 

[manti]

You would classify any kind of leaf removal as defoliation, and in studies you count the percentage of removed leaf mass. In the papers I posted the ranges went from 20% to 90% removed leaves, producing different results.

 

[skunkd0c]

You would classify any kind of leaf removal as defoliation, and in studies you count the percentage of removed leaf mass. In the papers I posted the ranges went from 20% to 90% removed leaves, producing different results.

by that definition i always defoliate , it does vary a huge amount depending on pheno/strain
as a general rule i may remove many leaves from sativa types, but i am always cautious when removing leaves from indica types
another general rule i will always try to keep as many healthy leaves as possible, i mostly remove overlapping leaves
and lower unsightly leaves that regrow into nice new ones
i do not believe that removing leaves causes any kind of hormonal growth spurt or benefits
i see it as "giving them a tidy haircut" which helps concentrate the light around the most robust branches of all the plants
and allows the air to circulate more freely when they are very close together

peace