In nature, earthworms consume decomposing plant matter, and if a compost pile is constructed, they will often move into it on their own when the plant material is broken down and the compost is completed.
When compost materials are piled up, or a compost bin is filled, bacteria will begin the breakdown process, which can generate lots of heat in the early stages. Compost piles can heat up to more than 65 °C (149 °F), effectively cooking everything inside.
Earthworms don’t have teeth, and can’t chew through tough plant materials, so they have to wait until the bacteria have broken their food down sufficiently for them to be able to crawl through and swallow. For this reason, earthworms will only move into finished compost, and that is only after it has cooled down.
Please don’t dump earthworms or compost worms from a worm farm into a compost bin, they will just get cooked, which isn’t very nice! Worm farms are used for compost worms (not earthworms) and are used to process fruit and vegetable scraps which break down quickly. In contrast, compost systems are used to break down garden waste, plant clippings and similar materials, which break down very slowly.
If compost bins are placed on the soil, earthworms will migrate into the bottom layers nearest to the soil surface where the compost becomes ready first. Earthworms will even find their way into compost bins placed on concrete surfaces. If conditions become unfavorable in the compost bin in any way, they make a quick escape to save themselves. Unfortunately, they have no means of escaping if they’re placed in a compost tumbler bins, which sits off the ground and spins to mix the contents. The aggressive mixing action of tumbling compost bins is great for aerating compost and producing finished compost faster, but it’s likely to crush any earthworms in there, so never place earthworms in a tumbling compost bin!
When gardening sustainably, it’s important to be able to read nature’s signs to be able to work more closely with nature. When you see earthworms in your compost, that’s how you know its ready, and that’s the time to put it in your garden.
Dig compost into the soil, or lay it under the mulch on the soil surface in no-dig gardens to prevent the loss of nutrients and beneficial bacteria. The earthworms in the ground will dig the compost deeper into the soil, and break it down further, making it more accessible to plants.
If you’d like to use the earthworms in the soil to do some vermicomposting, then you can build an in-ground worm farm!