Earth Worm Castings: Natural Manure Fertilizer
Earthworm castings, basically worm manure, have become a popular natural fertilizer among gardeners who want to be eco-friendly. Harvested by worm growers who practice vermiculture (raising worms scientifically and according to professional standards), worm castings are either bagged as they are straight from the worm or made into a tea (liquid form of castings) for use in the garden or on the lawn.
Worm castings provide a completely natural, organic, slow release of nitrogen and phosphorous to garden soil. Unlike synthetic chemical fertilizers, worm castings contain living microbials, bacteria and minerals beneficial to plants and lawns. Worm castings are fairly odor-free and safe for child and pet contact. The actual ratio of nitrogen:phosphorous and bacteria/microbials varies according to what the worm is fed and other environmental factors (soil, water, compost, temperature) in which the worms are raised.
The earthworm’s digestive tract processes the nutrients, trace minerals available in the soil (in which the worms are raised), and reduces them into chemically simple molecules, which are then easily available for plants to feed upon. This is a very important point to remember: Earthworm manure makes a great lawn fertilizer because the nutrients are readily availble, meaning RIGHT AWAY! This means a quicker green up when compared to other slow releasing natural fertilizers. But there still is no concern with burning the lawn either… it is a win-win situation!
In addition to naturally occurring nitrogen, worm castings contain small amounts of phosphorus and potassium and the trace minerals iron, calcium, magnesium, sulfur, boron, copper, zinc and manganese. Like other organic fertilizers, worm castings also naturally contain auxins and cytokinins, which are plant growth hormones that encourage root development and more fibrous roots.
Given the slow release of nitrogen and other plant nutrients in worm castings, there is no danger of over-fertilizing or burning the fertilized plants. A related benefit is that worm castings are cylindrically shaped and will not compact into solid, airless masses under normal conditions, something synthetic chemical fertilizers are prone to do with run-off and puddling after watering in. This characteristic of worm castings creates a fertile, healthy and highly aerated growing environment for plants.
The nutrients in worm castings are enclosed in mucus membranes secreted by the earthworms, which dissolve very slowly and have good water retention capability. If applied heavily to the soil, the castings can protect plant roots from extreme temperatures, minimize surface erosion and even help to control weeds to a small degree.
Worm castings would have great benefit to lawns as a natural organic fertilizer, but the relative expense of worm castings compared to other organic fertilizers such as Milorganite and Ringer is a significant drawback to their widespread use on lawns. The normal recommended application of worm castings for both established and new lawns is 10 pounds per 100 square feet. (Milorganite fertilizer is 18 lbs per 1,000 sq feet for a comparison) This means that if you use worm castings on your lawn, you will feel like you are literally shoveling the stuff into the turf. 
With worm castings at retail outlets usually selling for a dollar or more a pound, application of worm castings to even a small lawn is expensive compared to the other organic options currently available. However, even applied at a lower rate, the worm manure can have a nice summer greening effect that does not push growth. I also want you to think of worm castings more like a general soil conditioner, rather than an overall full-on fertilizer.