After a worm ingests organic matter, the material undergoes a change that is nothing short of a miracle. As Thomas J. Barrett once put it, "they (the worms) literally serve as colloid mills to produce the intimate chemical and mechanical mixture of fine organic and inorganic matter which forms their castings (excretions). In the mixing which takes place in the alimentary canal of the worms , the ingested materials undergo chemical changes, deodorization and neutralization, so that the resultant castings are a practically neutral humus, rich in water-soluable plant food, immediately available for plant nutrition."-(Harnessing the Earthworm, 1976)

Humus is beneficial to plants in at least three very important ways:

By "capturing" toxins which are present in the soil. Humus (which is organic matter) has a high capacity to fix heavy metals in materials such as sewage sludge, farmyard manures, crop residues and peat, preventing plants from "taking up" more of these compounds than they need, then later releasing them when they are required. By acting as a "buffer". Humus can help plants overcome soil pH levels that are either too high, or to low. An acid loving plant can still do well in a somewhat alkaline soil (and vice-versa), if large enough quantities of humus are present. This is due to the way humus prevents extreme pH levels from rendering soil nutrients "unavailable" to the plants.

As a growth stimulator. "Experiments on wheat, barley, potatoes, grapes, tomatoes, beets, and other crops show that even in very low concentrations, humic acids (contained in humus) act to stimulate plant growth. Tests to determine just how humic acids work revealed that they are in an ionically dispersed state. In this form they are readily assimilated by the plants as a nutrient, over and above any normal mineral nutrition that plants get. "-(The Rodale Book of Composting, 1992)

All of these benefits to plants, and more, are obtained by the presence of humus in the soil, and worm castings simply put, are biologically-active mounds that often contain as much as 40% more humus than is normally found in the top six inches of soil.

Are Worm Castings more nutritious than regular compost?

Yes! As material in a compost heap decays (becoming humus), the various nutrients undergo chemical changes which make them more accessible to plants. In addition to this process, however, worms also reduce the overall volume of the material even further as they remove the ingredients necessary for their own survival, growth, and reproduction (mainly bacteria, rotifers, etc.) Thus, with the remaining substances compacted into less volume, the actual nutrient percentages rise accordingly. It had been noted by several researchers that earthworm castings usually contain more "total and nitrate nitrogen, organic matter, total and exchangeable magnesium, available phosphorus, base capacity, and moisture equivalent" than their surrounding environment."-(C. A. Edwards and J. R. Lofty, in "Biology of Earthworms", 1977)