Raised Beds Over Poor Soil - Knowledgebase Question

Lillian, AL
Question by michey
May 26, 1998
My soil is 6" of sand overlaying a hard clay. How deep should I build raised beds for a variety of perennials, annuals, bulbs, and maybe a shrub or two? Should I mix purchased topsoil with the native soil to build the new beds?


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Answer from NGA
May 26, 1998

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It is a good idea to "transition" soil from one type to another. Plant roots will cross over into another soil type better if the interface is not so sudden. I would place about 4" of new topsoil in the bed area, rototill or spade it into the native soil to mix them a bit, and then add another 4-6" and repeat the mixing of the surface 8" or so. Mix some well decomposed compost (or composted bark) into the new topsoil you are adding if it doesn't already have some included. Your beds can be about 10-12" high for most annuals and perennials. If the lower clay layers are truly impervious, I would suggest 12-16" for the shrubs.

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