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 the removal 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 re-direct the energy of the plant into other areas you desire more growth from, most of the pruning should be performed in the growing phase of the plants life cycle.
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, ‘Lollipopping’ is actually just pruning.
Defoliation is widely considered a very controversial topic as there is no hard science on exact best practices to achieving beneficial results, the best answer here from our perspective is do what you feel works for you and your environment or what you feel is best for the plant, huge bushes with droopy overgrown leaves that have exhausted themselves hide a lot of the younger nodal growth waiting to emerge so logic tells us it might be a good idea to defoliate in instances like these.
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 prune or defoliate or not?
Unfortunately there is no clear and reproducible 'best' answer, and the truth lies somewhere in the middle.
There is a common link with the community agreeing that if defoliation in flower were to go ahead then days 21 & 42 are the days you could remove the major leaf mass to allow more light in, but again this is not fact, more observer effect.
“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.”
“I’d agree with that, it’s always worth pruning and training throughout the growth cycle to help the plant along. We also have a small window within the first few weeks of flowering (up to approx. day 18-21) where we can apply small amounts of pruning and defoliation to the under-canopy the redirect energy to the most important branches so they develop and yield much heavier.”
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.