To Defoliate Or Not To Defoliate
Interesting topic. I have tried both as probably most growers have I suspect. Based on my experience, I did not see a real difference when performing aggressive defoliation versus not, but each grow is different no? Different strains, maybe a slightly different nutrient mixture, different challenges (pests, temps, humidity, etc) so unless all things are equal it's hard to draw a real conclusion. I have never practiced any defoliation when doing an outdoor grow other than some lower branches that might be laying on the ground.
Where I have landed is to defoliate just enough to facilitate easy watering and that's about it. Since I normally do a SOG style grow, when I move into flower I might take off a few lower branches that are not seeing any light since doing the SOG creates a thicker canopy for the light to penetrate. However, based on the information from the article I might stop doing that too. Seems logical that the more leaves you have to process any available light the better. I mean if they are green they are contributing something to the overall health of the plant right?
Also, I used to pull off leaves when they started to yellow, but stopped doing that too. My thought is the plant is taking nutrients from that leaf for a reason so if I pluck it, won't the plant just adjust and start taking nutrients from another leaf...and so on. Now I wait until the leaf it slightly brown and about ready to fall off before I remove it.
One thing that was not clear to me from the article though. As you progress through the flowering stage and buds start to appear on lower branches, I will take a leaf or two to allow the light to get to buds that are being shaded. Not a lot, just one here and there and it does seem to have helped those buds get a little fatter. Is there any real value in doing this or not? Other than it make me feel like I helped that little bud 😎
I don;t defoliate per se but rather prune. I grow in Greenhouses and we always lollipop lowest 1/3 or 1/4 of the plant (depending on their size) in order to help control pests. Often with mite or aphid infestations, they tend to start lower down so we don't give them a foothold. The only other time leaves may be removed is if a particular leaf displays any sign of mould or rotting.
When I was growing outside, the only pruning of leaves I would do would be a few days before the end of the grow, when I would start removing yellow fan leaves. This was to improve airflow and try to help cope with mold problems (humid continental climate here). It also made the trimming job easier!
This is my first grow indoors with good climate control, but I am still absolutely paranoid about mold. So, I'm looking at the jungle of leaves in my tent, I'm concerned that even with exhaust fan, intake fan, and two circulation fans, I'm going to end up with insufficient airflow and mold. I remove any leaves that are too close to the growing medium and any leaves that are wilting, to reduce the spread of pests and pathogens.
I did prune a number of leaves and took cuttings for clones near the end of veg, mostly out of paranoia.
I am doing a scrog, and have been removing some leaves that shade the growing tips that I am tucking. I assume that this will reduce total growth of the plant, but if it allows the outer growing tips to catch up a bit to the rest of the canopy, I'm willing to take a little reduction in total growth for better growth on those distal tips. For the same reason, I am planning on scropping a few runaway stems this week to bring them down to the level of the rest of the canopy. With limited space and artificial light, I want to give every bud in the canopy a decent chance.
Interesting article. There are a few conclusions that I question. Specifically the assertion that relative yield of quality buds can not be increased. And the second that light doesn't affect inflorescence morphology. I used to push back against recommendations of defoliation very hard. I don’t anymore. My thinking went, fan leaves should be evolutionarily optimized for photosynthesis; then the sugar is translocated wherever the plant needs it. However, while there is still a lack of legitimate research, watching MiamiMango's results made me reconsider a blanket rejection of deleafing. It should also be noted that even he stresses his techniques are strain and grow-system dependent.
Even if it is true you end up with the same "total photosynthetic yield" when you defoliate leaves, that concept only holds in reference to potential biological yield (total plant biomass). Economic yield (yield of desired plant product or part - in our case mature inflorescences), could be improved by forcing plants to partition yield to marketable plant parts, rather than leaves, thereby raising the harvest index. Cannabis stems and buds are green and photosynthetic too, not just its leaves. Perhaps in a cultivated state, under some circumstances, it’s more efficient to have a flower-only canopy with deeper light penetration than to use the leaves. Leaves are fast and easy to grow compared to flower and stem. In the wild a plant needs to compete for light to survive, which means quickly claiming light resources before it is crowded out. If competition is removed, maybe it is more productive for a farmer to eliminate leaves and force production of (the still photosynthetic) inflorescences.
The 'flowers' of Cannabis that people refer to as buds are actually inflorescenses and comprise mostly non-flower material. Cannabis flowers are extremely reduced, with the only obvious part being the receptive stigmas (visible part of the pistil). Nearly all of a Cannabis 'bud' is leaf and stem material, consisting mostly of bracts and bracteoles. The calyx is reduced to a membraneous ring, if it persists in cultivated Cannabis. Second, the morphology that is claimed to be altered (increased bud density, increased resin production, higher potency) occurs not among the floral parts, but among stem and leaf tissue: reduced stem elongation between flowers along the stem of the inflorescence, increased resin on leaf tissue, increased cannabinoids within that resin. Therefore, whether there are or are not photoreceptor proteins inside the flower tissue is moot. Light intensity definitely can affect phenotypic plasticity of Cannabis inflorescences (even if reduced density of lowers may only occur secondarily as a result of less light recieved by their directly subtending source leaves).
Interesting points, @growinghigher. If I can improve my cloning technique sufficiently to be able to reliably get similar=sized clones, I would love to do a common greenhouse experiment to test for at least one strain. I really need a larger tent than my little 120x60 to get adequate replication, but if I grow as a sea of green in smaller pots with frequent fertigation and do no other training, I should be able to squeeze in enough replicates.
I keep going back and forth on the experimental design. My initial thought was to randomly assign each location in the tent to either the no-defoliation "control" or defoliation treatment, but then I realized that shading from neighboring plants could well impact the defoliated plants more than the no-defoliated. Then I considered splitting the tent in half, however I know that my light has a non-symmetrical radiation pattern. Then I considered dividing the tent into 4 quadrants by placing both longitudinal and transverse reflective dividers, and then randomly assigning two of the quadrants to each condition.
All that sent me down the rabbit hole of looking at the most recent studies on common greenhouse experiment design, including https://plantmethods.biomedcentral.com/articles/10.1186/s13007-019-0527-4 and https://www.researchgate.net/publication/321382388_Incomplete_block_designs_for_plant_breeding_experiments and I decided I'll let someone else do the study.
Hi growing higher. Thanks for your thoughtful input.
Even if it is true you end up with the same "total photosynthetic yield" when you defoliate leaves, that concept only holds in reference to potential biological yield (total plant biomass). Economic yield (yield of desired plant product or part - in our case mature inflorescences), could be improved by forcing plants to partition yield to marketable plant parts, rather than leaves, thereby raising the harvest index.
You are suggesting that leaves are sinks and influence the partitioning of photosynthates in plants. Which is not the case. Leaves are sources and are always sources once they reach maturity. This is not a hypothetical concept. But a theoretically proven and visually observed property of leaves when they transition from low photosynthetic organ sinks to high efficiency photosynthetic sources. Once leaves reach maturity and have transitioned to a fully self sustaining source (produce energy in excess of their own demands), they remain sources for the extent of their life. When they reach a stage where they can no longer continue to support their own resource demands. They begin senescing and breaking down left over potential resources for transocation. There is no relative partitioning effect with leaves and so no potential gain from a proposed leaf sink hypothesis.
Cannabis stems and buds are green and photosynthetic too, not just its leaves. Perhaps in a cultivated state, under some circumstances, it’s more efficient to have a flower-only canopy with deeper light penetration than to use the leaves. Leaves are fast and easy to grow compared to flower and stem. In the wild a plant needs to compete for light to survive, which means quickly claiming light resources before it is crowded out. If competition is removed, maybe it is more productive for a farmer to eliminate leaves and force production of (the still photosynthetic) inflorescences.
Color is not indicative of photosynthetic ability. Some plant species can carry out photosynthesis in their stem or floral components. But their primary function is of nutrient/fluid transport and structural integrity with stems. And reproduction in flowers. They are not very good at all at providing significant photosynthate resources. And when in the absent of leaves, they lack the potential to continue development, let alone stay alive. This is why cannabis cannot revegetate when all leaves have been lost, including bracts (sugar leaves). Its also worth noting that the primary function of bracts (sugar leaves), are not for photosynthesis. But reproductive enhancement purposes. Such as protection, shelter and attraction. Where many plant species show poor photosynthetic potential in bract leaves. So we have to expect the possibility that cannabis bracts are not as effective at photosynthesis as primary leaves. But even if they were, this show no obvious advantage.
The 'flowers' of Cannabis that people refer to as buds are actually inflorescenses and comprise mostly non-flower material. Cannabis flowers are extremely reduced, with the only obvious part being the receptive stigmas (visible part of the pistil). Nearly all of a Cannabis 'bud' is leaf and stem material, consisting mostly of bracts and bracteoles. The calyx is reduced to a membraneous ring, if it persists in cultivated Cannabis.
Yes this is my understanding in floral anatomy also. I have tried to educate other growers about the correct anatomical descriptions of cannabis flowers. But the traditional terms have stuck. But we at least all mostly know what we are referring to when talking about floral components. So it does not worry me much.
Second, the morphology that is claimed to be altered (increased bud density, increased resin production, higher potency) occurs not among the floral parts, but among stem and leaf tissue: reduced stem elongation between flowers along the stem of the inflorescence, increased resin on leaf tissue, increased cannabinoids within that resin. Therefore, whether there are or are not photoreceptor proteins inside the flower tissue is moot. Light intensity definitely can affect phenotypic plasticity of Cannabis inflorescences (even if reduced density of lowers may only occur secondarily as a result of less light recieved by their directly subtending source leaves).
This seems to be primarily focused towards trichome morphology. Which is not what this article is intended to be about. We are talking about the primary yield influences. Not the qualitative characteristics of trichomes, which we are all for and understand about. Its well known about trichomes photomorphological responses towards light, and so is not up for discussion in this topic. But at the end of the day. Light morphology has no influence on floral development. And trichomes are not part of this. Which is what the articles point of floral morphogenesis was about. Floral morphogensis is primarily determined by internal processes (genetics) and is not influenced by environmental factors, such as light. As such you will not find any material or subjects on the matter of floral responses to photomorphogenesis. It doesn't exist.
"The significance of these changes in relation to soil nutrient dynamics and plant nutrient uptake during regrowth require further exploration." https://link.springer.com/article/10.1023/A:1004787710886
I also enjoyed reading this
It makes for an interesting topic daily, especially in the cultivation of cannabis. Cultivating Cannabis sativa L. (Cannabaceae) differs from other horticultural plants by the end product that is harvested. The total yield cannot be rated only by the weight of the flowers; the chemical composition of the end product is also in the interest of the producers and end users.
Different cannabis chemotypes contain numerous chemical compounds, such as cannabinoids, which are known to exert various pharmacological effects. Morphology and cannabinoid profile are dependent on genetic and environmental factors.
For a medicinal cannabis producer, a continuous and uniform yield and production of a specific cannabinoid compound or a ratio between the different cannabinoids throughout the canopy and between growth cycles is important.
I love your explanations and how informative you are @drphoton. At the end of the day, I've been much happier leaving the leaves on, my yields are more significant. Especially since I use pretty much all biomass in some shape or form.
I only prune leaves away to control environment or produce more potential potency on lower flowers. I've noticed anything that is heavily shaded will take longer to develop and quality is diminished. The Springer article was kind of cool though, I'm going to look into more about the soil biology.
Maybe we are talking around each other here. But to me, trichome development on the inflorescences (not flowers) across the entire plant determines the marketable yield (economic yield) from that plant. Trichome development therefore is germane. I don't think the claim about defoliation was ever that it yields more plant material, (or even necessarily flower like I suggest with the partitioning of inflorescence vs leaf); it is that it yields more marketable product (high density, high resin, high potency).
Defoliation and yield with cannabis has been primarily associated with each other in almost all material and discussions i have been in. Anything else of interest has been of secondary focus. Most arguments i have brought up are what the general public use for their reasons on using this method. The use of defoliation for improving the "marketable" yield is not what would be considered the ideal or most effective way for managing the translocation patterns in plants. If you are growing plants that produce wasteful material that does not meet the standards for usable produce. Then you are not practicing the best methods of pruning and plant training to maximize "marketable yield". If done right, you should have little to no waste from your harvests.
Maybe. Maybe not. This one I need to see data on. There definitely is some photosynthetic capabilities in the stems, but more importantly the leaves on the inflorescence. The leaves on the inflorescence are likely as efficient at photosynthesis as the large fan leaves. Defoliation is often focused on "water leaves" and the largest fan leaves. Cannabis has a near continuous variation from these leaves to single leaflet bracts or the highly resinous and specialized "calyx" bracteoles around the flower.
Although i agree that the reduced leaf bracts do photosynthesize a significant amount. Its best not to assume that they are "likely" as efficient, when research on other plant species show that they typically are less effective at photosynthesis than regular leaves. For example cotton and poinsettia bract leaves, although can look like regular leaves. Only produce a fraction of the photosynthetic capacity of regular leaves. Bracts are modified leaves with at times, much different anatomical and physiological structures, which usually completely differentiate itself from a primary photosynthetic leaf. With its main evolutionary purpose for being supportive to the reproductive process. With the observation from other species on photosynthesis, it is best to assume the possibility, that it cannot compare to a primary photosynthetic leaf. To extend on this, observation on perigonal bracts (not to confuse people with reduced leaf bracts) have indicated to have very little to no photosynthesis capabilities. This has been observable by not only myself, but others who have experimented with total defoliation, including reduced leaf bracts (sugar leaves). Where only the reproductive organs (pistillate and perigonal bracts) are left behind. Where the result was the total inhibition of growth and the gradual senescence of the plant. Showing a poor response of perigonal photosynthesis to continue floral development and or even the sustenance of itself.
The total leaf area probably stays similar, even when defoliation techniques are used, it is just shifted to the smaller leaves. Some varieties are so shaded by their own fan leaves, only the top few inches of a cola produces material marketable as smokeable flower.
Yes this is the natural characteristics of the translocation patterns in plants. Which are governed by factors such as proximity, vascular connections and development. Light can only really penetrate roughly 12 inches of canopy, depending on the anatomical and geometry of the leaf and genetics used. And so floral development below this point will naturally be lower compared to above this point. Proper management of plants by modifying the translocation pathways through pruning and training practices allows the grower to control the development of cannabis flowers to the growers demands.
I can understand your point of view with regards to marketable yield and photosynthate partitioning. However it fails to recognize key fundamentals with plant physiology and cultivation practices. Where we can already maximize marketable yield effectively with traditional pruning and plant training practices. With no limitation or restrictions on canopy light capture or photosynthetic efficiency. Interesting discussion however and appreciate the thoughts. 🙂