70x70answered grow question 2y ago Defoliation is a tricky word, but the reason is the most important. Always defoliate when humidity is too high; if it's not coming from outside, it's probably due to the combined transpiration of all the leaves or if visible moisture and shade form on the buds due to overlapping. Removing a few poorly positioned leaves or entire side branches here and there isn't so bad, but it does delay growth by a few days, which for me is part of the plant training, so in that case, from about week 2, selectively removing a few well-chosen leaves. However, this requires a little plan on how you want to fill your growing area, keyword mainlining. Additionally, you can lollipop, meaning removing about the lower third of the leaves; the timing is a bit tricky since it causes stress for the plant, so energy goes into healing instead of growth for 2-4 days. Despite the delay, it makes sense because very little light reaches that low down to derive real benefit from it, and there have been earlier quantitative experiments where an increase in yield was found. This only applies to indoor growing where effective space utilization is important; outdoors, I believe it's just about preventing mold when defoliating.