How to encourage composting worms to migrate upward

Question

I have an upwards migration worm composting bin that currently has three trays. In recent months, I had done a poor job ensuring that the moisture level in the top bin was reasonable, and it got out of control and got pretty wet for a while. The worms did not seem to like this.

After several weeks I was able to get the moisture under control. However, the majority of the worms are now in the bottom tray which is mostly already composted material. I don't imagine that there is a whole lot of food/resources in that bottom tray, so they must have been pretty unhappy to move down there and stay there. I also note the middle tray is pretty empty of worms as well.

Is there a good way to encourage the worms to leave the bottom tray and move back up to the top tray where the new food is?

Answer 1

Some of the worms could be reintroduced to the upper & middle trays manually, and a small amount of the tray material/ soil exchanged at the same time along with the manual worm transfer. In the short run, a small amount of nutrient suitable for the worms could be added to the bottom tray to maintain the worms' health. After the worms are somewhat reestablished in the middle & top trays, they may begin migrating more again. The prolonged wetness of the material in the top tray may have become more compacted/ otherwise reduced in suitability to the worms, so checking the top tray for that could be useful.

In addition to the lesser moisture content of the bottom tray, the temperature of the bottom tray may also be more optimal for them, so measuring & monitoring the daytime temperatures of each of the the three trays and measuring & monitoring the night time temperatures of each of the three trays, could be useful. If the bin is in direct sun during the day, that could increase daily temperature fluctuations, especially for the top tray.

If there were initial differences in the materials put in the trays could affect the worms' migration. Good question; if you could include an image of the bin, and its dimensions, could also be helpful.

Answer 2

I have had the stackable trays for over 4 years now and I think I can say that, empirically, the worms don't seem to want to move up, even with optimal conditions and food source, mine just won't do it in large enough numbers to matter. I now rotate the trays around. It's possible I am doing something wrong but just rotating the trays was my solution. To that end, I also placed a screen in the bottom of the last tray not under it as the destructions suggested. That is the tray that I empty onto the garden or top tray depending on winter/summer. This is still a Wip but so far so good.