Building a raised garden bed on an incline can be tricky. If your garden area is on a hillside, you will need to have higher sides on the downhill side to retain the soil. If it’s only a slight incline, you may be able to level the box by placing the higher side into a slight trench to level it.
However, if your incline is too steep, or you don’t want to dig a trench, here is a simple way to make a level garden bed which sits on the ground and requires no digging.
This box is built with some leftover 6′ privacy fence *panels. We used uncut boards for the front and back, and cut a board in half to make the sides of a 3′ x 6′ box. The corner posts for our box are cut from a 2″x2″ cedar post. The lengths of the corner posts are determined by the desired box height, and the amount of slope you are working with. We had an 8′ post and cut it into (4) 2′ lengths.
A common size for a raised garden bed is 4’x8′. Anything wider than 4′ will make it hard to reach everything without stepping into the bed, which compacts the soil. The length of the box is determined by the available area, materials, or personal preference. The number of boards needed depends on the size of the boards and the width, length and height of your box. Pressure treated wood, which harbors toxic chemicals, is not recommended. Cedar is naturally insect and rot resistant.
Decide on the desired size for your box and cut a board for the front, back and 2 sides. If you are going with the common 4′ x 8′ size, cut (2) 4′ boards for the sides and (2) 8′ boards for the front and back. Attach the end of one corner post to the end of one side board at a right angle. You should have something that looks like the image above.
Place it on the hillside where you want your garden box to sit. Using a level, mark on the downhill post where the other end of the board will need to be attached to the post. Repeat for the other side. Be sure to hold the side boards level when marking.
The next step involves cutting and attaching the lower side boards to match the incline of your hillside. Place the 2 sides flat on the ground, and lay another board on top as shown in blue. Mark off and cut to match the incline, then attach to the side. Repeat for the second side.
Our box required just one board cut diagonally with the scrap fitting the other side. Depending on the amount of slope in your garden, you may need to use more than one board to fill the area.
Complete the box by attaching all four sides to the posts. At this point, the front (downhill side) of our box has 2 boards and the back has one board. The sides each have one full board and one diagonally cut board. Ours is off a little at the bottom post, but we figured it would be covered by dirt anyway. 🙂
The boards can be attached to the outside of the corner posts, or one outside and one inside. You can see in the photo below, we attached the short sides to the outside, and the long sides to the inside. We felt this would provide a little more support on the long sides once we filled it with soil. If needed, we will pound a 3′ rebar in the ground on the outside of the long boards, for additional support to keep them from bowing out.
After placing the box on our incline, we decided to add another row of boards around the top to make it taller and help keep the bunnies out. We were going to cut the posts even with the box, but decided to use them for a trellis / support system.
If you have moles or other digging creatures, you could line the bottom with wire cloth before filling with a quality compost and soil mixture.
This project used (8) 6″ cedar fence planks and (1) 8′ 2″x2″ cedar post.
*We had some leftover fence panels so decided to use them for this raised garden bed. They are thin wood and won’t last as long as thicker wood, but hopefully we will get several years’ use with them. 🙂