The length can vary depending on the availability of gently sloping space, ease of material handling, or other factors. Longer windrows will cost a little more for supplies. To start a windrow, spread a 12 to 18 inch layer of manure solids, with or without bedding, along one end of your available space. For this first row, apply 1lb redworms per square foot of windrow surface area. Each windrow should be large enough to hadle these thin layers of material each week.
Larger volumes can help protect the worms from adverse conditions and predators.
Enclosed bins are still recommended for home or school-based vermicomposting. A hard or concrete surface is easier to work on, especially in wet weather, and may even be required to control runoff. This method does not generate high heat. This is acceptable for many types of dairy or horse manure. If heat treatment is needed to control pathogens or weeds, simply pre-compost the material before feeding to the worms.