leaves don't hold nutrient reserves, stems do. buds are able to produce up to 30% of their own carbohydrates through photosynthesis.
Effect of Pruning on the Yield and Quality of Kinnow Fruit
The Photosynthetic Activity of Cox's Orange Pippin Apple Flowers in Relation to Fruit Setting
the above links to peer reviewed scientific journal articles aren't the most comparable to cannabis, but there isn't much peer reviewed content out there as far as MJ goes. the concept is relatively simple and so is the physiology behind it, so when you consider the following testimonies, the evidence is pretty conclusive:
"I SCROG for an even canopy and remove energy wasting leaves; IMO defoliating/pruning/de-leafing is more about energy management than light penetration. Plants aren't aware we're there to manage their canopy for them, and so use vital energy to branch out and produce those big fan leaves. "
"I'll be honest. I used to think it sacrelige to remove beautiful looking leaves. Not to mention there seems to be a blank spot when you first do it. It is common practice in many species to remove leaves to promote fruit/flower growth. (another thing I didn't know....until i started growing vegetables) One of the more extreme cases I can think of off hand is brussel sprouts. In some climates you will not get sprouts without topping the plant and removing nearly all of the leaves. Even in zones where this is not necessary, gardeners remove nearly all of the leaves to "promote fruit growth." By removing the large leaves that take an enormous amount of energy to support the plant is able to "concentrate" on the smaller leaves it takes to make the sprout.
Now none of that has a damn thing to do with MJ, but once tested it is hard to argue with. Now some stretchier strains have plenty of room for buds to get light and ventilation. I agree that there is no need to remove leaves from these strains. Other strains that grow very dense do not only benefit from the extra light they receive, but also benefit from the increased circulation."
"If a top or branch is running away (getting too tall) I cut it. Once my space is full, I switch the lights. Once a week, I remove each plant so that it can be cleaned up. At this point I remove any leaves that are 50% dead. Next I place the plant in its home, give it a quarter turn, and remove any big leaves that are shading buds. I also look for leaves that are lying directly on top of other leaves, as leaves left in direct contact with each other do not do so well. If a leaf is lying on a bud, I do not tuck it, I pull it because it usually seems to pin itself against another bud. (another thing I don't want)
Sometimes in a weeks time, so many smaller leaves will become shade leaves that I do not pull them all. I like to remove shade leaves but not to the point of causing major stress. This is why I prune each week. It allows me to pull a couple of leaves and give the plant time to recharge."
"I consider de-leafing an advanced technique, and should be left to the pro's. If you are new to growing, use the K.I.S.S. ( keep it simple stoner) method, until you feel comfortable with pruning and de-leafing. Its all in the eyes of the beholder, it takes many many years of cultivating to get an eye for the plant. You need to read your plants, they will tell you what the want.
If your leaves are dying or yellowing, that tells me that you have a deficiency, and your plant is eating itself. Do not remove it. Let the leaf fall off by itself, it needs the nutrients stored up in the leaf. Larger leaves take more energy to maintain themselves, and will rob nutrients from the buds. By removing the large fan/ shade leaves, it forces the feeder leaves to grow larger. Larger feeder leaves = larger buds. I do most of my pruning and de leafing in veg, to allow the plant to recoup. before Bud. I also prune and de-leaf at week 3 Bud, and again when I start my flush. That opens up the plant to give maximum light to the bud sites. The more light the more sugar. Think of the sugar as sunscreen, the more light hitting the bud the more trichome will be produced. If leaves are blocking the light the less trichome the bud will produce. "
"With the wisdom of over 30 indoor crops of the same strain, in the same environment...
After several mistakes with indoor watering schedules, I have had plants (about half way through flowering) lose the Majority of their leaves!! In the end, the flowers were almost as fat and tight as the plants which survived the drought..
In a super intensely lit indoor environment, with no cloudy days, plants receive ample light. Heck, there is practically enough photosynthesis going on in the green buds alone!! Big shady fan leaves are redundant, and not necessary in a properly lit indoor environment!!
Yes, I prune fan leaves, especially those closest to the bulbs, mercilessly!!
Be strategic though! You don't want to remove them in such a way as to allow light to pass right through a plant and hit something that isn't green (ie: pots, soil, floor, wall). As long as all of the light is hitting some part of the plant, what's the problem?? Even distribution of light, throughout the plant, is the aim...."
