I have a small backyard with very little level ground and plenty of shade. I wanted to expand my garden, but the prime real-estate was up a six foot incline to my back fence. It took a lot of digging and what seemed like endless root cutting from a former maple tree to tame this hillside. I ended up with: four 4x8 beds, one 8x8 bed, four 2x4 beds and some additional areas for shade plants at the top.
Per 4x8 bed
6 4x3/4''x8' (pressure treated fence boards)
1 cu yds of generic garden soil
1/2 bag sphagnum peat moss
2 bags compost manure
2 bags quality garden soil (miracle grow, etc.)
Step 1: Building the frames
I decided to make the first beds using mortise and tenon joints because I liked the look. It looks similar to a bed frame when assembled. I used my router with a guide attached and a 3/4'' spiral cut bit. This made the 3/4'' side fit tightly in the mortises. I made several passes, gradually plunging deeper each time to achieve the desired depth of the mortise to prevent overheating the bit.
Dry fit everything to make sure you haven't made any mistakes before digging your footings. Because these beds are set into a hillside, it is best to anchor your 4x4 posts in the ground.
Tip: Make a Story Stick to mark the position of every cut and mortise. Use your Story Stick to mark each board, rather than your tape measure. This makes marking your wood much faster and will ensure uniform cuts on each piece.