That is an excellent question, I’ve wondered that myself. I believe that it’s probably best to harvest a little bit here and there during the growing season. Last Fall I picked off nearly all of the leaves just before I brought them in for the winter. I also severely pruned several of them just so they would fit through the door. I lost several large kratom plants during the winter, and that’s never happened before. The surviving plants didn’t thrive last summer like they usually do. However, I also opened the air vents in the room that I overwinter my plants, so it was a little warmer and drier. I typically do neglect my plants in the winter, but I never lose very many, and certainly no large plants. Also, I just had way too any plants in that room, I couldn’t even walk around in there. I have since thinned out my plants by nearly 50%. So it’s hard for me to say if it was the neglect or the extreme harvest/pruning that was so detrimental to my plants. Either way, I do not recommend doing a massive end of the year harvest, even though most of your leaves will probably dry up and fall off during the winter. Maybe taking 50% is OK, but don’t pick them nearly clean like I did. BTW, it was the good old Bumble Bee variety (and one Green Malay) that survived. Even though they are all (except GM) very similar, Bumble Bee is the best for us in the Northern Hemisphere. It grows the fastest, is easiest to root cuttings, and tolerates adverse conditions the best. Keep an eye out for spider mites this winter, I get them every winter like clockwork. I’m going to overwinter mine in the garage this year where it’s colder. I’ve done it successfully with a large Bumblebee before, it went dormant quickly and completely, it never got spider mites, and it bounced back next Spring.