How to fertalize with worm castings
Worm castings are not classed as "fertilizer". Their contents are far from being equal to the chemical / petro chemical fertilizers available on the market today. When all is said and done however, worm castings are better for the soil, better for the plants, better for the rivers and lakes, better for the planet, better for your health and better for sustainable agriculture!
Castings do not have 30% nitrogen content but they do not kill every living thing in the ground either. There, I feel a bit better having gotten that off my chest...
Casts or 'castings' are what the worms excrete, ergo, what went into the worm is what is in the cast. Worms change, in their digestive tract, the organic materials, minerals and gases as well as compounds and organisums which would be otherwise detrimental to plant growth, into soluable (plant usable) forms. They use very little of what they consume volume wise, digesting for nutritional use mainly microbes like bacteria and passing the rest as casts.
Almost all of what the worm eats is concentrated, reduced in volume and weight without loosing it's mineral, good microbal, or nutritional value or content and all that is neatly wrapped up by the worm in a semi-permiable mucosa which is itself valuable nutritionally to plants. Studies have shown that worm castings are ruffly 5 times as rich as the soil or medium in which they were created. Casts are made up of what is available to the worm so nothing will magicly appear in the cast which was not present to some degree in the consumed medium prior to ingestion.
The above mentioned studies were of worms in feral or 'in the ground' states and not of worms held in boxes or bins (or such is my understanding). Boxed, food scrap and rich compost eating worms obviously enhance the structure of what they are fed as well and, I am sure, manage to concentrate those nutrients in their casts. How concentrated these sorts of castings are, I can not say for sure but, if you take horse manure as an example feed, at 25C/3N and weighing in at say one ton, then being reduced by the worms to about 200 lbs. of castings, it would seem, at least on the face of it, that those 200 lbs. would be some pretty nifty organic plant food.
Well, if it sounds like hype, so be it... but it's not some fantastic fabrication! Check it out: Worms eat your garbage, excreting casts. The process binds the nutrients consumed into plant usable form, reducing the volume of the original materials and adding good soil building micro and macrobiotics to the mix. The worm casts are covered by the worms with a slow dissolving, semi-permeable mucus which is both a time release mechanism for the cast's nutritional value and the source of it's extraordenary water retention capabilities. What is fed into the worms then, is converted into a mild, topsoil or humus like pseudo-fertilizer which will not "burn" plants, cause oxygen starvation or other unwanted problems when mixed with the soil of your garden or placed as a mulch layer on potted plants etc. Additionally, assuming that what you fed the worms was solely organic and environmentally stable, the casts are perfect to go on food crops which are to be grown and sold as "Organicly Grown". To really get a grip on that one, go on down to the local 'organic' grocery store and see what one of the tomatoes costs. Castings can be mixed with potting soil (1/3 casts to 2/3 potting soil) to make fantastic seedling starter.