A question often comes up about putting composting worms in soil, perhaps in a garden bed. My personal experience says that worms will live quite well in a garden bed, provided there is a very thick layer of organic mulch. Composting worms live in the decaying mulch, not in the soil.
But is that really true? There are 2 schools of thought. One, which I have always advocated, is that composting worms only live in the decaying organic matter. The other is that composting worms will burrow into the soil if temperatures get too cold for them to survive in the mulch.
Last fall, after my vegetable garden succumbed to the first frost, I applied a very thick layer of organic mulch to my garden beds. The mulch was mainly shredded cardboard, but also included some leaves. I also put what I would call a poor man’s subpod into each garden bed. I bought plastic file boxes, the kind with holes on each side and the bottom, from Walmart, buried one about 2 inches into the soil in each garden bed and set each one up like a worm bin. I added a small handful of worms to each one. I piled the mulch up against the sides of this subpod to keep the bedding from drying out, and to encourage the worms to wander out into the mulch, if they wanted to.
the subpod thing had varying success. This spring half of them had a healthy worm population, and half did not. But then I got a surprise.
There are worms in the mulch in all of my garden beds, even the ones in which the subpods have no worms. But I got an even bigger surprise as I was planting my tomatoes.
When I planted my tomatoes, I started by trimming off the lowest side stems from the main stem. I then dug a hole much deeper than needed. I put a handful of worm castings in the hole, and planted the tomato plant up to just below the lowest remaining side stems. This causes the tomato plant to grow a stronger root system, since roots will grow out of any part of the main stem that is buried.
This also meant digging holes about 6 inches deep into the soil. And I found composting worms in the soil as I was digging each hole. These worms were adults, full size and very healthy. The soil has been amended with a lot of horse manure, so they had plenty to eat.
So, will composting worms live in soil? Under the right conditions, it looks like they will. But I wouldn’t count on it. I would still go for the thick layer of mulch, and let the worms decide if they also find the soil suitable.