1) with red wigglers, the castings are everywhere (species check: Canadian nightcrawlers can't live in a bin). To harvest them in a flat bin, you have a few options. I am lazy and have 4 bins or so, 3 of them small. In my small bins (almost trays), I turn on the lights, take off the lid, and after a bit I use my bare hand to scrape off some castings. Those have many cocoons and I tend to add them to containers. In my big flat bin, I move the whole mass to one side, and I start filling the other side. Eventually the worms completely process the old side and mostly move to the other.
My favorite bin is my worm bin bag from instructables dot com. Great project to do with someone who can run a sowing machine.. I'll edit with a pic. With the bag I just open the bottom and harvest the casting that fall out. I feed at the top. Easy as pie. Actually, I often use "unfinished" castings from a plastic bin as bedding in the bin bag. Hey, alliteration!
2)worms are predators. Ever see or read Dune? To microbes, the worms are just like sandworms. Well, some actually live in the worm I'm told, but that's the basic idea. At the same time, they don't eat all the microbes, and they grind up microbe food so they can eat it faster. Microbe food is what? Plant and animal waste and flesh and
matter. So why do worms help plants? They have evolved to ensure their own survival. More plants, more microbes. They help plants in so many ways it is too much for a forum. If teaching a three year old, wigglers are a great non-emotional intro to the benefits of natural predation. Just like wolves ensure the health of the elk population, worms ensure the health of the microbe population.
3)I cringed when I saw the video clip of Martha turning a worm bin. Bad move. If your bins need air, drill more holes or make a bin bag, and change your feedings. Try drying out the scraps a bit or using different bedding. Ambient humidity and temperature are factors aMing others.
The easiest way to mess up early on is over feeding. Remember they can live on the bacteria in your bedding, so it's almost impossible to starve them. If you have 30 worms, that's maybe the peels from one potato per day, not more. Be patient.
Important tip: Healthy soil and plant matter from various ecosystems outside are very important. For one, the grit is useful, for two, you are introducing local soil biology - the best kind.
I got a million tips, as do others on this site, but especially for a 3 year old, an intro to microbiology from a well informed parent is a powerful gift.
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