Outdoor windrows or beds, either in heaps or in beds with low simple walls, are
the most common type of process generally used. The size of such beds is flexible, but
the width of the beds should not exceed 8 ft (2.4 m), which allows the entire bed to be
inspected easily. Because there is no need to walk on the bed, many suitable surface
coverings and construction materials can be used. The length is less important and
depends on the ground area available. They should not be laid directly on soil because
soil particles would be picked up with the processed vermicompost. Concrete areas are
ideal for earthworm processing systems because they provide a firm surface for tractor
operations. However, it is essential for precautions to be taken to prevent too much water
from entering the beds and to allow excess water to drain away from the bed easily.
Often, the wastes on such floor beds are covered with some permeable material such as
canvas or bamboo sheets, which permit watering and need be only removed for addition
of new waste materials. Windrows and floor beds process organic wastes relatively
slowly, often taking 6 to 12 months for complete processing. During this period, there
may be significant losses of plant nutrients through volatilization or leaching. The major
drawback to windrows are the difficulties in harvesting the vermicompost and the need
for a trommels or other labor-intensive separation stages to recover earthworms from the
vermicompost before it is used. Although the initial capital outlay, other than land, is low,
large areas of land are needed, labor costs are high, and the rates of processing are slow.