A couple of things I think are worth mentioning when growers bring up "defoliation". No amount of nutrients will help the plant grow, unless they are first processed through the leaves. Only then, may mobile nutrients, commonly called "plant food" continue to the buds, for growth. The real name for plant food is called "photosynthate", but for the purpose and ease of this post, let’s use the term "plant food".
Leaves" have two main purposes:
1st, You can thank the leaves themselves for 99% of all the uptake of water and nutrients. Plants have a very small chain of water molecules that stretch from root to leaf, within the "xylem" (the woody center part). This ionic chain phenomenon is referred to as cohesion, whereas the entire uptake, from root to leaf, is called "transpiration". Water is basically the blood of the plant. If you cut any leaves off, you limit the plants resources of water.
2nd, Leaves make all the "plant food" that the plants use to grow, while managing waste (O2), through the stomata. The stomata are very small pore-like openings in the bottom of the leaf, that exchanges new CO2 and O2, and water evaporation. "Plant food" is made through a process called photosynthesis, with in the chloroplast. Leaves are like a big food engine, but instead of 2 fuels like a car (gas & O2), leaves have 3 fuels (CO2 & Nutrients & PAR).
So, why remove them?
I've never liked the term of "defoliation" as it means "to strip (a tree, bush, etc.) of leaves", implying all of them. I prefer to use their relative nick-names, "lollipopping", "schwazzing" or even "pruning", to limit confusion. These methods are not something I would promote anyone who desires larger yield, especially outside in full sun or if using auto-flowering seeds. Realistically, removing "any" healthy mature leaf will hinder growth & yield. A good rule of thumb would be to let the plant itself decide naturally what she wants to keep.
Distinguishing the different terms of training, or pruning growth is also a factor. Pruning a branch off the main stem, to manipulate growth direction, is not defoliation. Defoliation includes only leaf matter.
Growth "time span", is also something that plays a roll. Depending on the cannabis grower's view, any plant manipulation while in vegetation cycle may not be viewed as playing a role in final yield, while referring to defoliation. As an example, a farmer could prune half the vegetation off in veg cycle, but gives enough time for the vegetation to grow back, before entering into flower. If the factor of "time" itself is removed, the outcome of yield could be viewed differently.
Buds, do NOT require any light. No amount of light that's exposed to the bud 'itself' will help it grow, or yield more. There is, however, redistribution of sugars through "sink" manipulation.
Where/what is this sink?
"Sinks cells" are areas of new growth with low osmotic pressure. Leaves are areas of high pressure, hence why "plant food" or post-photosynthetic nutrients, flow from high pressure leaves, to low pressure sinks; commonly called "osmosis". Sinks can be in the roots or the shoots of the plant (new growth). After the plant food has been manufactured in the leaves, it enters into the phloem, starting at an area in the leaf called "source cells". From here, osmosis carries "plant food" to its destination and use.
Younger leaves always use more processed nutrient (plant food) than they can make through their own photosynthetic actions, and must draw from other leaves. If they are removed (in flower) the plant food that would have gone to them for maturing, would be redirected to the remaining areas of "sinks". This works for buds too. Any buds removed, allows plant food to flow towards remaining sinks.
Finally, there's one more thing to consider, called "relative osmotic location". Basically, the closer the mature, healthy leaves are to the sink location, the faster the plant food arrives, and the more efficient the growth process is. Leaf location matters. It’s also worthy to note that all leaves work as a collective, with light PAR. Nothing changes 'how' the plant food is manufactured because of location of leaf removed.
There are two main defoliation methods that cannabis growers can choose from.
1) They can focus on upper colas by removing under developed, lower growth (leaves & buds alike). Generally speaking, this is the method that will yield the most, with very large colas on top, but you may be victim of a larf (popcorn) sized buds below. This method is often referred to as "lollipopping".
2) They can focus on a more consistent size bud throughout the plant, by removing larger leaves above. This method forcing the plant to mature lower leaves evenly, thus causing "relative osmotic location" to enhance lower growth and size of the sinks directly around them. This method generally yield much less because the younger leaves are sinks as well, and compete directly with the bud's sink strength, on the available plant food. The lower buds will ripen with a larger, consistent size, but the upper colas will suffer and yield less. This method is often referred to as "Schwazzing".
Now for an overall recap. Nutrients use the water to hitchhike a ride, up the xylem, to the chloroplast in the leaf. The leaf processes the raw nutrient into plant food. Then, plant food, enters into the phloem, and high pressure pushes it throughout the plant to areas of low pressure and use.
As standard rules while in veg cycle go:
Any healthy, mature leaf removed "will not" effect over all yield size.
Any healthy, mature leaf removed "will" hinder overall growth speed.
As standard rules while in flower cycle go:
Any healthy, mature leaf removed "will" effect over all yield size.
Any healthy, mature leaf removed "will" hinder overall growth speed.
