Vermicomposting, worm bin, composting with worms community and forums
Excellent to hear your worms are taking off.
I'd say the bedding ought to be touching the upper bin. It could take quite a while for the worms to get hungry enough to get all the bottom-dwelling worms to migrate up, depending on how rich the conditions are in the bottom bin.
At first I tried building up the compost in one corner of the bottom tray hoping that the worms would find this convenient ramp. It didn't happen.
I also had my top ramp setting on small blocks of wood because I was afraid that it would squash the worms in the bottom tray.
I've since changed everything. I threw away the blocks of wood and let the top tray sit directly on the bottom, and I clear one corner of the top tray of everything except garbage scraps. Yesterday when I lifted the top tray and looked at the bottom of it, there were a lot of worms hanging under the corner with the food scraps.
I don't know how much this helps, since you have multiple bins and I have just one. But we have the same problem, that we want the worms to migrate out of old compost into new compost. So, for what it's worth, here is a diagram of my bin (sorry, I'm no artist):
I made two bags out of this loose plastic mesh called "bird block". The bottom bag contains the older compost. There's a hole down the middle of that compost, that I filled with the cardboard tubes from toilet paper and paper towels, when I put that bag on the bottom. The tubes eventually disintegrate, but for a while I think they help prop it up and create an airway. The top bag has new compost, with an empty hole down the center that I just maintain by hand. Again, this is for aeration.
About every 3 months, I take out the bottom bag, empty it, and swap the bags. I loosely fill the hole in the new bottom bag's compost with tubes. The newly empty bag goes on top, and I continue to gradually add bedding and food as if nothing had happened. I have to hand-sort the contents of the bottom bag, using the "light" method. Clearly, this is the worst part of my strategy. But I expect it's at least no worse than stacking trays. I observe that after 3 months, around 90 to 95% of the worms have left the old compost for the new. There are always quite a few stragglers and bottom-dwellers that I have to manually return to the bin, as well as any unfinished material.
That's a great idea - thanks! I think one of the problems is, my trays are really deep. And if yours took 3 months to migrate maybe i'm doing ok. So I will give them a bit longer and when I can get them to move I may re-arrange my system as well.
So when you take out the top bag to change them over, the worms don't fall down or get squashed when you put it in the bottom?
Actually, I don't know how long it takes to get them to migrate. I imagine that after some time has passed, the old compost becomes less interesting because I'm not putting new food in it, and the old food has all been processed; then gradually more and more of them would gravitate towards where the action is. I'm sure it's a very fuzzy transition, analog not digital. :-) The three month cycle came up because that's when my bin starts looking full, and getting really heavy, which makes me realize I need to harvest the VC.
As for casualties during the operation... as far as I know, there have been very few. It's a messy job, and some fall out onto the concrete, and need to be rescued. If I've done them harm directly by moving the bag, I haven't seen it. Actually, I always fear that they could be caught between the net and the compost, and get sliced! But I have never seen any half-worms, so as far as I can tell, that hasn't happened. I try to move slowly as I pull the bag around, to give them a reason to get out of harm's way and time to do it. Also I don't put the bag immediately back in the bin. I left out the part where I lay it out temporarily, so I can hose out the bin and clear clogged drainage and ventilation holes. This may be an opportunity for them to retreat deeper into the compost.