Total cost about $80. Total time about 1 hour.
Tools: Cordless drill and a miter saw (but easy enough with a circular saw or even a hand saw.)
Materials: two 5 step stringers, and five 8-foot x 5 1/2-inch cedar boards. A box of 1 5/8-inch cedar color deck screws.
Step 1: Use a Pair of Outdoor Stair Stringers
The key is to turn them the wrong way to make them steeper than as used for stairs.
Create boxes out of cedar boards- drill pilot holes (to prevent the boards from splitting) and use deck screws to screw the boxes together.
Cut the boards to length, (we used 28 inches) and cut end pieces at 4 3/4 inches. The ends will fit inside the sides (you can build your boxes however you want, this is just how we did it, its all an aesthetic thing)
The cedar boards have a smooth side and a rough side, we built ours with the rough side out- again its just an aesthetic thing.
Step 2: Attach Two Boxes to the Stringers
We screwed the bottom box and the second-to-the-top box to the stringers. This holds it together, but leave the other boxes removable, this makes it easier to move around.
Fill the boxes with good soil and plant whatever.