Top soil is loaded with micro-organisms which will immediately begin to break down the organic matter. Top soil can be taken from your garden or purchased. Composted material can be used as a good source of desirable micro-organisms. This is all that is necessary, but you can hasten the process by taking some other steps. Some materials produce a slightly acid condition in the decomposition process.
Lime is basically calcium carbonate, and is usually in the form of ground limestone or marl.
It is sold at most farm and garden supply stores. Do not use lime in the compost if you plan to grow acid tolerant plants such as blueberries. Use of hydrated lime is not advisable. Commercial Fertilizer Bacteria use large amounts of nitrogen in the process of organic matter decomposition. Add fertilizer high in nitrogen to each layer to help feed the bacteria.