When we make a compost tea, we are using either worm castings, thermal compost, or both as the starter to culture the tea from.
When we refer to compost as “thermal” it means that the materials in the compost pile have been broken down and digested by microbes that created heat in the process. This is natural and particularly dramatic with compost that is turned and aerated frequently. It is very important that we use well aerated compost for our compost tea brews because the type of bacteria we want in our teas are aerobic–oxygen loving bacteria. Thermal compost piles also may have high populations of fungi, which is good for most types of compost teas.
How to compost?
There are many good books on the subject. In Compost Tea Making by Marc Remillard we outline the basics of how to make compost specifically for compost teas. It may not be rocket science, but it is soil microbiology, focusing on compost tea production. We do down-play the use of manures but that is honestly a very conservative approach. If you use manure from a known source that is free of antibiotics your compost will certainly benefit.
The standard ingredients like grass clippings, leaves, sawdust, manure, and kitchen scraps will make great compost as long as it is turned and aerated often. Just make sure it contains enough “brown” carbon source materials like leaves, sawdust, and clean cardboard. If you add a little forest soil to the blend it will introduce beneficial fungi as well.
How to compost?
Worm castings make great compost teas that are bacterial dominated. Worm castings have a lot of good benefits for the soil. In Compost Tea Making by Marc Remillard we have a fairly long chapter discussing the latest, most current techniques involving the growing of composting worms. Depending on the climate where you live, specific species of worms are used for composting. Eisenia fetida, or Red Wigglers, are the best composting worms for temperate climates. Red wigglers are heavy feeders, shallow dwellers, and reproduce rapidly.
The common earthworm may be beneficial for soils in our environment but unfortunately they do not behave well in shallow worm growing systems. They are deep burrowers, and like to travel the world (escape from enclosed systems).
In warm climates where soil temperatures never drop below 50 degrees F. many worm growers swear by Indian Blue worms, which have many common names and may be of least two species; Perionyx spenceriella, and Perionyx excavitus. various worm species can be purchased from online sources. Use the species names to ensure you get the exact worms you need. Common names are confusing.