A few choices of building materials for the structure of a raised garden bed include pressure treated lumber, cement blocks, or simply a perimeter of rocks, stone, or even logs.
PT Lumber for raised garden bedsMost all raised garden beds are built from lumber, that is, pressure treated lumber (PT). PT wood is ideal in any high moisture and/or ground contact installations. Why use pressure treated lumber for raised garden beds? It prevents rot and insects from prematurely destroying the wood. What is pressure treated lumber? Pressure treating is a process that forces a chemical preservative deep into the wood. The PT process starts with the wood being placed into a large cylindrical holding tank where much of the air is removed. Then the tank is filled with the preservative under high pressure, which forces it deep into the wood. The tank is then drained and the leftover preservative is reused. Prior to 2003, the type of wood preservative that was used in residential and commercial structures included ‘arsenate’. It typically had a green hue to it. Due to health concerns, during 2003 the industry switched to a preservative with either copper or chromium. It typically has a dark brown hue to it. The ‘stuff’ comes off readily, so you will want to wear gloves… Of importance to note is that this newer type of PT lumber requires the use of hot-dip galvanized or stainless steel hardware. Anything else will quickly corrode. A good size PT lumber for garden beds is 2 in. x 12 in., the 12 inch height is plenty for the soil. Don’t be tempted to use 2 in. x 6 in. even though it costs less and may seem easier to deal with – it’s not tall enough to accommodate the amount of soil you will need. Other typical sizes include 2 x 8 or 2 x 10, which should be Okay for the depth of soil. Typical PT lumber for garden beds (data from Home Depot) 2 in. x 12 in. x 8 ft. PT Hem-Fir Lumber, copper azole coating 55 lbs each $19.97 Materials cost, 3 x 8 foot raised garden bed using PT lumber (about $50) (2) 2 in. x 12 in. x 8 ft. = $40 Hot-dipped galvanized screws = $5 Tax man = ~$4
Concrete Block for raised garden bedsAlthough pressure treated lumber will last many years, a raised garden framed with cement blocks will essentially last forever. It will be a bit more difficult to ensure a nice level top flat surface plane while placing the blocks to form a perimeter, and some people may not find the look as appealing as lumber, but it will last, and is a good alternative. One difference is that the typical concrete block is 8 inches tall, so the bed height will be a bit shorter than the wood framed example. Typical Concrete Block (data from Home Depot) 16 in. x 8 in. x 6 in. Concrete Block 24 lbs each $1.38 Materials cost, 3 x 8 foot raised garden bed using cement block (about $24) (slightly less than 3 x 8 foot inner dimension) (16) 16 in. x 8 in. x 6 in. = $22 Tax man = ~$2
Rocks/Stone/Logs Okay, the rest is up to your imagination. Depending on the ‘look’ of your yard and surrounding geography, any of the above may suit you just fine, and may cost you nothing to build.
The point of the article is to hopefully encourage some of you to start thinking about your garden plans, to consider a raised garden bed and the materials that you will frame it with.
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