Yesterday I made a few pallet planters for Dear Wife...
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The first one was too big (24X24 inches), so I made a second planter (16X16 inches), and that was too small. 
 
So, I'll be making another planter, maybe this time 12X24 inches rectangular, and hope that passes her inspection.
What I liked about the bigger 24X24 inch planter is that I was able to find some dark pallet wood and alternate that with lighter pallet wood. I did that on all 4 sides and I think it looked good. Just too big, I guess.
I then made the smaller 16X16 planter, but learned a valuable lesson. The pallet 2X4's in the smaller planter were not all the same size. So, my planter got out of square. I had to cut the final wall piece on each side on a taper, and finish it off with a planer to fit. Not a huge problem to overcome, but the top of the planter was a good 1/4" wider than the bottom. Does anybody care? Probably not. But having to cut the wood on a taper and plane it down to fit burned up extra time. Lesson learned - next time make sure the 2X4's are all the same size.
Benefits to this design is that the 2X4's inside the planter are hidden, so I was able to use the parts of the stretcher that had the cut-outs for the forklift. No waste on those 2X4's with this design. Also, on each wall side, I added the wood from the outside, left and right, and worked my way to the middle. The last piece of wall board will probably have to be cut down to size, but that was easy. Even on the smaller planter that got out of square, the last wall piece just had to be cut down on a slight taper, and planed to fit.
I topped off the planter with 45 degree cut 1X4 planks. I simply took the measurement of the side (24 inches, for example) and added 1 inch for hangover to each side = 26 inches on the long cut. Then I used my miter saw to cut 1 board with the 45 degree cuts, and used that board as a template to cut 3 more exact sized boards. That saved some time and energy as no measuring was required on subsequent cuts.
I don't plan on staining or painting these planters. But would ask for some feedback on that issue. If they only last 3-4 years, that will be good enough for me. I might line the inside of the planter with a plastic garbage bag before filling up with soil, that should help preserve the wood a bit longer.

 Any feedback appreciated. Thanks.