Soil & compost
How many boards do I need to build a raised bed?
Perimeter divided by board length, times the number of courses. A 4x8 bed one board high needs three 8-foot boards; two courses high needs six.
How this works
Boards per level = perimeter ÷ board length, stacked until the bed is tall enough. Near food, use untreated cedar, white oak, or black locust — never old treated wood.
Questions people ask
Is pressure-treated lumber safe for vegetable beds?
Modern treated lumber uses copper rather than the arsenic compounds banned in 2003, and most extension services now call it acceptable. If you would rather not, cedar, black locust and untreated douglas fir are the usual alternatives.
How wide should a raised bed be?
Length is free; width is not. Keep beds under four feet across so you can reach the middle from both sides without standing in them and compacting the soil.
How long will an untreated bed last?
Cedar and black locust run 10 to 20 years. Untreated pine or fir is closer to 4 to 7, which is fine if you accept rebuilding it.