Slopes are a natural for raised gardens, since you have to create terraced beds anyway to level the ground. The benefits of raised gardens include more control over the soil and better drainage, and more oxygen, for the plants. Building raised garden beds on a slope can be accomplished without much digging, and the results can be quite compelling.
Measure your slope and draw it, to scale, on graph paper. Plot your raised garden beds, figuring each one to be 4 feet from front to back. Divide the length of the slope (from the lowest point to the highest) by four; this is now many raised beds you can build, each stretching from one side of the slope to the other.
Start at the very back of the slope and lay down a layer of bricks or blocks, first using your shovel to cut into the slope and create a small level trench, about 2 or 3 inches deep, for the bricks or blocks to sit in. Once you have the initial layer installed, add three or four additional layers, depending on how deep you want your raised bed to be.
Now measure out 4 feet down the slope. Hammer in stakes at the 4-foot mark. Then take your 4-foot-long 2-by-4 inch board and lay it on the back brick extending out to a stake. Place your level on the board and raise the board until the little bubble is in the middle; with a pencil, mark the point where the board meets the stake. This is how high your next block or brick wall should be.
Again, create a level trench, 2 or 3 inches deep, to act as a foundation for the first layer of blocks or bricks, and then start layering until you reach the desired height.
Measure out another 4 feet down the slope and pound in your stakes. Bring out your 2-by-4 inch board and butt one end against the bottom of the wall you've just built. Once again, raise the other end until it is level and mark the spot on your stake. Build another wall, and repeat, if necessary, until you are all the way down your slope.
When finished, you should have several rows of blocks or bricks stretching all the way across your slope. Now comes the fun part: filling in the dirt. Use good-quality topsoil, available at any home improvement store or garden center, and fill to a depth of 3 inches below the top of the front wall.
Your final step is to plant away. Raised gardens on slopes are great for vegetables, but they also can be beautiful additions to your landscaping. Try roses, or put leafy perennials in the back beds and annuals in the front beds.