UPDATE on my planter(s) build for Dear Wife.
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As I said in an earlier post, my first attempt was the middle 24X24 inch planter, which was deemed too big. My second attempt, on the left, was the 16X16 inch planter, that was judged too small. My third attempt, on the right, is a 12X24 planter and I surely hope it hits the Goldilocks' zone and is just right for Dear Wife! I'll find out when she gets home from work today. Wish me luck! 
Let me add, that I have learned something on every one of these pallet builds. Nothing like experience to improve your production. My last planter was more square from the start, required less custom cuts to finish the fit, and it went together much faster because I am learning how to cut the boards more efficiently.
Although I am very happy with this planter design, I think I will be trying out a few other designs I have seen on YouTube. One of my ideas is having the planks mounted on the inside of the 2X4 frame. Since a 2X4 is 3 1/2 inches wide, that would give me about 7 inches of play when mounting the planks on the inside. That would mean I doubt if I would ever have to custom cut or taper that final board for the sides. I would just take up any difference(s) with the overlap on the inside 2X4.
Something like this google picture...
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