How Deep Should a Raised Bed Be?

Usually, lumber (such as cedar) will come in a standard size that’s 6 inches in height.  In other words, the sizing is 2 inches x 6 inches x 8 feet. (Note that boards bought at a lumber yard are actually 1.5″ thick x 5.5” high.)

You could also stack the two boards. The height of two stacked “2 x 6″ boards is 12 inches (technically 11 inches).

You can certainly go taller (18 inches, 24 inches, 36 inches), but note that the weight of the added soil will add pressure to the sides. You’ll need to add cross-supports to any bed over 12 inches high.

Consider what you may grow. The depth of the soil itself is very important and depends on how much soil depth the crop needs belowground. For example:

• Deep-rooted crops such as carrots, parsnips, potatoes, tomatoes, and squash need a minimum soil depth of 12 to 18 inches. If plants don’t have loose soil to this depth, the roots will not be able to go down deep enough to access nutrients.
• Shallow-rooted crops (such as lettuce, greens, and onions) need a minimum soil depth of 6 inches.

To place it safely, you could just ensure your beds have a depth of 12 to 18 inches. Whatever height you choose for your frame, you’ll need to loosen the soil below the ground accordingly. For example, if you have a bed that’s 6 inches high, we recommend loosening the soil below the ground about 6 to 9 inches if you wish to grow root vegetables. If you are only growing shallow-rooted crops, there’s no need.

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