Vermicast, or worm castings, is the material earthworms excrete after digesting organic matter. It is a fine, stable, humus-rich soil amendment with high microbial activity. Worm tea is a liquid brewed from it.
1How it forms
As food passes through a worm's gut it is ground in the gizzard, mixed with mucus and enzymes, and inoculated with gut bacteria. The result is small, stable aggregates that hold water well and release nutrients slowly.
2Effect on plants
Its value lies less in the nutrient numbers, which are modest, than in its biology and humic substances. Trials report better germination, root growth and resistance to some pests when vermicast is mixed into growing media.
3Worm tea
Worm tea is made by steeping castings in aerated water for 24–36 hours, so the microbes multiply and soluble nutrients pass into the liquid. It is not the same as leachate, the liquid that drains out of a worm bin, which can be anaerobic and should only be used heavily diluted.