Answer: The depth of the soil in your garden plot will depend on what you're growing. Most annual vegetables and flowers would like a minimum of 8" of top soil to grow in. Any perennial planting would do better with at least 12" of soil to grow. To calculate the amount in cubic feet multiply 16 x 20= 320 feet square feet time the depth (say 8") at .8= 256 cubic feet of soil. One yard of soil is 27 cubic feet so you'll need a whopping 9 yards of soil to raise the 16 x 20 foot area 8" high. That's a ton ofsoil, so it would be better to create smaller riased beds in that area to sue less soil, but get as much benefit.
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