A great thing about raised-bed gardens is the diversity of materials you can use to build them. Some gardeners opt to spend a mint for decay-and-insect-resistant cedar boards; others use whatever wood, concrete blocks or other building materials they have lying around. If you have some wood slats from an old pallet or some other source, you can use them to build a raised garden bed. Because slats tend to bend easily, you may need to provide some extra support to keep your soil and plants where they belong.
Cut each slat to 4 feet long, using a saw. If your slats are already a uniform length that is slightly longer or shorter than 4 feet, that's OK -- just so they're all the same length. You'll need 16 slats for this project.
Stack four slats on top of one another and measure the height with the horizontal edges touching. They will form the walls of your raised bed.
Cut 4-by-4-inch square posts into lengths that correspond to the height you measured in the previous step. Depending on the width of the slats, this could be anywhere from 8 to 16 inches. The posts will be set at the corners of the raised bed, acting as anchors to which you'll attach your slats.
Place one 4-foot-long slat against the bottom of a 4-by-4-inch post you just cut, with one end of the slat flush with the outside edge of the post. Attach the slat to the post with a 2-inch screw
Place another slat flush along the top of the first slat, and use a 2-inch screw to attach it. Repeat this process until all four slats are attached to the first post.
Attach four slats to the other outside face of the post, forming an "L" shape with the slats already attached to the post.
Repeat steps 4 through 6 with a second post, so that you have two posts, each with slats attached to form an "L" shape.
Arrange the two L-shaped constructions to form a square; place the remaining two posts at the corners that don't have posts. Drill screws through each slat and into the posts.
Place the frame you have built where you want your raised garden bed to be.