Pruning and Defoliation
Pruning and defoliation are two very different things but often confused with one another.
Pruning is the removal of any plant matter, usually with the intentions of manipulating growth and development of the plant. Pruning can be as simple as removing old branches, removing undesired growth or cutting back a plant to reduce its overall size.
Defoliation is technically a type of pruning, except it specifically refers to removing of leaves, generally fan leaves, with the intention of allowing more light and air flow around and through the plant.
How to further distinguish the differences between pruning and defoliation?
Pruning is utilised to remove entire sections of the plant to prevent it from continuing to grow and direct the energy of the plant into other areas you desire more growth from. When a section of a plant is removed, the plant notices the change of mass and will redirect its energy supply across its remaining mass.
Defoliation targeting specifically leaves can cause some major problems, if over-done.
Defoliation is widely considered a very controversial topic as their is no hard science on exact best practices to achieving beneficial results. Some growers swear by heavy defoliation for increased yields and high efficiency growth, while others choose to do little to no defoliation and let the plant take its natural course.
What's the best decision? To defoliate or not? Unfortunately there is no clear and reproducible 'best' answer, and the truth lies somewhere in the middle. Personally I tend to do minimal defoliation and only when I feel it must be done to prevent mould or humidity issues in dense foliage scenarios where dew may form or to prevent the shade avoidance response from the plant.
The risks of defoliations during flowering/fruiting
Defoliation done during a vegetative growth cycle is a non-issue as the plant is only producing mass and leaves. The risks open up when defoliating during flowering/fruiting, where the plant has generally stopped producing vegetative growth.
Defoliation done correctly, will open up your plant to allow more light and air to flow freely between your branches, generally improving environmental conditions around the plant itself, such as better humidity levels, air (CO2) flow and light penetrating down to the lower canopy.
Defoliation done incorrectly usually occurs when the grower strips crucial leaves or too many leaves from a plant, effectively removing the energy stores and ability to absorb energy (photosynthesis) from those areas of the plant that the leaves were removed from. This often results in aborted or under-developed flowers/fruits from the regions that the leaves were removed.
As a general rule of thumb: if you are going to remove leaves during flower/fruiting cycles, its best to never remove a leaf from an area that does not have additional supporting leaves nearby to take over the role of the leaf you just removed.