If you have a shaded spot on your property, a worm pit (or bed) can serve a number of helpful purposes (not to mention entertainment!). First off, the biodiversity they offer in the form of both micro organisms and fungi, will surpass that of castings from a normal worm bin. This is so because of beneficial constituents like leaf mold, bacteria, Mycorrhizal Fungi, and even certain mushroom mycelium.
This is the richest soil that “money can’t buy!” Another plus to a worm bed is that they offer a place to put your surplus worms should you not want to keep expanding your bins (just be aware of environmental impact on introducing some worms).
I started my pit by just adding yard debris, leaves, kitchen wastes, cardboard and paper, partially decomposed compost from the hot bin, and even pieces of log and wood chips. I then started mixing in bags of coffee grounds that are given away free at most coffee shops (Starbucks etc.).
As can be seen in the picture, I have done something a little different in mine by partially submerging a couple of varieties of logs inoculated with mushroom spawn. The ones that I have are the reishi mushroom and the elm oyster, and these have a symbiotic relationship with the micro organisms in the soil. However, it is not necessary at all (from a compost standpoint) to add mushrooms into your pile. In fact, native mushrooms to your area (probably inedible) will find your pit and start laying down mycelium in the soil. As mentioned, this is excellent for both the worms and the later soil. When I dig through my pit, I see this broad network of white, “cottony” stuff.
Because I have ample space, my pile is a little untidy and it would probably be a good idea to add something like cinder blocks around the border. You might also consider digging a bit of a sunken pit to help with temperature and moisture control. Just make sure that you don’t dig it down deep enough where it might flood! Also, depending on how close you are to neighbors, you might want to beware of certain ingredients that might attract varmints (though my pile never does smell). Be sure to place your pit away from large trees because they will love the soil and invade (though frequent digging therein discourages them).
Because worms basically utilize the microorganisms attaching themselves to the foods, it might take a few weeks before native worms will be drawn to the pile. However, the addition of nitrogen rich components like coffee grounds and even a little diluted urine, will greatly speed up the process. Adding some molasses or other sugars will help speed up microbial activity (thus enhancing worm activity etc.).
In my Florida area I have a native “super composter” worm called the blue worm (more generally called the Perionyx excavatus). It’s only drawback is that it will die in temperatures below 45 deg F and it likes to “explore” a little too much for some folks with indoor bins. However, I have a hunch that if it was introduced to a sunken pit in colder climates, it might fair okay due to the insulation and natural heat generated by aerobic activity. I also keep the P. Excavatus out of my normal red worm bin just in case it might out compete and deplete them. In a nutshell, if you live in climates where natural worm activity is not sufficient, you can just add the desirable redworms (red wigglers, Eisenia foetida, etc.) and other composting worms that are generally available. If you give these worms a good home in your pit, they will remain and become compost and casting factories for you.
When I want compost from the pit, I just scrap away the surface layer down to the seasoned compost and then shovel it into a wheel barrel or other desired container. If you wish for the worms to remain in the pit, just separate using any of several techniques. Stay tuned as I will be adding many pics and observances from the worm pit!