Answer: To some extent the answer to your question depends on the quality of the existing soil. The first thing to do is to run some basic soil tests and find out how good (or bad) the soil already is. Your County Extension (599-6162) can help you with the tests and interpreting the results in terms of what you need to add -- or don't need to add. Then, before you actually build the beds you need to loosen and fluff the soil beneath in order to avoid creating an impenetrable layer between the native soil and the bottom of the raised bed. Once you have done that it will already be raised a bit from the original level. It is always a good idea to add as much organic matter as possible (a twelve inch layer is not too much), so use compost, rotted leaves, aged stable manure and bedding etc. and incorporate that into the soil. The best specific material is usually determined by availability and price and varies from area to area. This will raise the soil even further but if it is still not high enough, the best addition is soil from somewhere else on your property. The reason for this is that imported top soil is often of questionable quality and may be a bad match to the existing soil. This can cause more problems down the road in terms of soil structure and drainage incompatibilities. Finally, remember to leave some clearance at the top of the bed to accommodate a layer of organic mulch. This, along with regular additions of still more organic matter, will help to replenish the soil on an ongoing basis.
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