What Are Worm Castings?
Worm castings are the excrement (or poop) worms produce after ingesting organic matter. They are also referred to as "vermicast," "vermicompost," and "black gold."
Worm castings are distinct from traditional thermophilic compost. Though both processes begin with organic waste, worm composting is performed at lower temperatures and the waste passes through the microbially-rich lining of the worm's digestive tract. This results in a product that contains a greater diversity and abundance of microbes, as well as higher nitrogen levels.
Notably, worm castings have a neutral pH (6.5-7.0) and can be applied immediately to plants without the need for curing or fear it will burn plant roots. It has an earthy smell and should not stink.
Most worm castings contain a small amount of bedding or uneaten material. Due to this, producers run their castings through a 1/8" sieve to ensure a more consistent product without worms, worm cocoons, or visible feed stock. Some will also brew their worm castings to make a "compost tea" that can be used when watering.