Tiered garden beds are great for adding visual interest to a garden while also helping segregate different plants. This instructable goes through the step by step creation of my garden bed, but please take the basic ideas and expand. The design I used is fairly simple and symmetric but the same steps could be used to make an intricate abstract masterpiece. I didn't need a back to the boxes since it was up against a fence, but it would be easy enough to add those if needed.

While I have a decent amount of tools, there are certainly tools that would make this easier (a bandsaw could notch the ends with 10% of the work). Again, modify these directions to work best for you.

One last note is if you could get your hands on some old railroad ties, they would work great for this project as well. They'd add a nice green touch while slashing the costs of the project. Unfortunately, I couldn't get my hands on any.

The materials I used are:
11x Pressure treating landscape logs ($4 each at Lowes)
2x 10ft pieces of 3/8" rebar ($4.50 each)
Lots of dirt.

Tools:
Miter saw
Table saw
Reciprocating saw (with metal and wood blades)
Hammer
Chisel
Tamper
Shovel
Drill with 1/2" Spade bit

Step 1: Cutting the Wood to Size

Each of the 4 main boxes is 28" long, 40" wide, and two logs high. I chose these because each 8 ft log cuts into exactly two 28" and one 40" section. I recommend waiting until you have the larger boxes set before cutting the connecting logs as this allows for minor changes in placement later on.

Step 2: Notching the Ends

Rather than butting the logs up against each other, notching the ends lets you stack them on top of each other and drive a single support through 4 logs at once. Given that the logs are 4" x 2.5", each notch should be 4" x 1 3/8." Making it slightly deeper than half of the log height will give more freedom when placing them. If you have a band saw you can ignore these details and just use that, otherwise I made due without.

You need to cut each each 40" piece on both ends and each 28" piece only one end. To set the blade depth of the saw take a scrap piece of wood and mark it at 13/8." Run each log through 4" from the end. Then set the table saw to max height and 1 3/8" from the fence. Run each log through vertically. You should have about 1" left that you will need to finish off with a reciprocating saw.

Step 3: Notching the Middle

Each of the bottom 28" logs (except for the two outermost) needs to have a second notch for the connecting logs. I did this by setting the table saw again to 1 3/8" high and cutting two slits slightly more than 4" apart. If you cut them exactly 4" you will have a really tight fit. Once the two slits are cut I set the table saw to 45 degrees and cut V's in between the slits. Finally, a chisel and hammer were the best bet to remove the rest of the notch.

I made the notches exactly halfway down the beams because I originally planned on planting the ground level. After getting everything finished I'm just going to let the grass grow right up to it, so if I had to do it again I would make the notches close to the end of the logs.

Step 4: Test Fit the Pieces

It's not a bad idea to test fit the pieces at this point. Once everything is all set you should have:

8x 40" pieces with notches at either end
6x 28" pieces with end and middle notches
10x 28" pieces with just an end notch

I actually mis-counted and put a middle notch in one two many logs, so I just screwed an extra block of wood back into the space.

Step 5: Cut the Rebar

The rebar needs to be cut into smaller pieces. You'll need 16 pieces and I made them about 14" each. You can also buy smaller pieces, but it's cheaper to just cut down large ones

Step 6: Prepping the Site

Two two boxes on either end get set first. You may need to roughly level the whole area if it's not already. You should also tamp down the dirt directly underneath the logs. It's easy enough to do the tamping as you go along.

Step 7: Setting Up the Boxes

Lay all the pieces on top of each other as they'll wind up. With all the logs in place drill a 1/2" hole in each front corner and on each side over the middle notch. Drill deep enough that the bit marks the lower level of logs, remove the top logs, and finish the rest of the hole. Set the rebar into the holes, but don't hammer it in yet.

Step 8: Set the Spacing for the Inner Boxes

Rather than measuring from the beginning, I just measured the proper spacing of the inner boxes once the outer ones were set. This is why I hadn't cut the connecting logs yet. Once you've got the placement set, setup the boxes just as in the previous step.

Step 9: Adding the Connecting Logs

Cut the 8' logs to the proper length and notch either end as before. Place the upper pieces back in place and use the existing hole as a guide to drill through the ends. Set everything back in place, insert all the rebar, and hammer it flush with the logs.

Step 10: Finishing Up

The only thing left now is to fill the tiers with dirt. If you need to buy dirt, ripped bags at Lowes are 50% off. It took 20+ 40lb bags to fill everything in as a frame of reference. It's still a little early to plant here in Buffalo, but hopefully I should get things going within a couple weeks.