Answer: If you place boxes over existing lawn and moss, there may be problems with drainage because the grass will act as a barrier. To be on the safe side, rototil or dig the area first. It isn't necessary to remove the grass, just break up the area so the new soil and the old soil will mix a little when you fill the boxes. You can use 1x12's but if your boxes will be three or more feet high, 2x12's will be more rigid and won't have a tendancy to bow outwards when filled with soil.
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