What nutrient content does worm castings contain (roughly)?
Worm castings’ nutrient content depends on the diet the worms have been fed with. To answer with a quote: “Analysis of earthworm casting reveals that they are richer in plant nutrients than the soil, about three times more calcium and several times more nitrogen, phosphorus and potassium.” (K.P. Barley, Advances in Agronomy, Vol. 13, 1961, p. 251) Usually plain worm castings made from variety of organic waste will support plant growth without additional nutrients for some weeks (3 to 5 weeks), although my experience is nitrogen and magnesium supplement doesnt hurt (with a N & Mg greedy plant). The worms will consume nutrients from the waste, naturally, into their bodies. This is not lost however, as the worms themselves make an excellent fertilizer (NPK 10-1-1 with high calcium and magnesium). Worm casting NPK numbers found on the internet range from NPK 3-2-2 to 0.5-0.1-0.1. Worm castings also usually contains high levels of other macronutrients and micronutrients, and while the three
