I actually always trim my buds fully before i hang, and in my opinion its the only way to harvest. And if your making bubble hash with your stems, have fun wasting your time, potentially ripping your bags, and making shitty bubble. Bubble really should only be made from your best sugar trim or any leaf with thrichs on it. I never would make bubble with fan leaves or stems cause there are no trichomes on them, and it will just add more plant material to your bubble. maybe some of your stems within the buds have trichs on them, but i wouldn't even waste my time with that. And the bottom bag isn't always the strongest, and it depends on what size bags you're running for your lowest. When trichomes break off, the break off right below the head generally and at the base of the stalk, leaving heads and stalks. The resin heads contain virtually all of the THC, with the stalk having a lot less THC if any. Indica resin heads are larger, so they get caught in the larger micron bags, and sativa heads are smaller and get caught in the smaller micron bags. Generally the best full melt bubble will come from either the 90µ or the 73µ bags. The small bags will get some good bubble as well, but the lowest bag (25µ) will contian a lot of the stalks of the trichomes, so I don't think it is the best.