The bed’s 4 sides each need 3 courses of timbers to rise more than a foot above ground, for a total of 12 timbers. Because it’s best to have full pieces on each side, buy stock lengths at least as long as the dimensions of your bed. Make sure each timber is straight and clear of knots on at least one side.

to make a railing to cap the bed’s walls

to secure the first course of timbers to the ground. These are usually sold in 18- to 24-inch lengths. Both are long enough to secure 6x6 timbers at least a foot into the ground.

such as Timberlok and Timbrex brands, to fasten the sides together.

to fasten the railing to the timbers

for drainage under the walls and at the base of the bed. Most home centers carry either 1/2- or 1-cubic-foot bags. To determine the cubic footage you’ll need for 3 inches of fill at the base, divide the square footage of your bed by 4. To figure out how much you’ll need for 2 inches of fill under the timbers, add the length and width of the bed (in feet) and divide that number by 6.

Most home centers carry 2- or 3-cubic-foot bags of properly amended soil. Because the bed is just about 1 foot deep (with the gravel layer at the bottom), the square footage of the bed roughly equals the cubic footage of soil you’ll need to fill it. Throw in an extra bag to account for settling.

For fastening 2x8 cap rails.