So my mom has all this junk wood she's been collecting, and I think I found a good use for it: as above-ground planters or as a vertical planter "post" (say 2 x 2 x 6 feet). Basically, fill it with soil and have planters coming off the sides.
Would I some how need to compensate for gravity and more water accumulating on the lower plant roots? Would this attract termites if I didn't use redwood (or cedar) but emptied it every year?
It's not necessarily a bad idea, but I think you'll find construction and use to be much more straightforward if you use the wood to build several smaller, shallower beds.
If you don't get the drainage right, the bottom of your planter will get waterlogged.
It isn't clear how you plan to plant into it, but it seems like it could be awkward to plant into it. Plant roots generally grow downward, so if you plant them on the side of your planter, they won't really be able to take advantage of the full depth.
Emptying a 2x2x6 planter (nearly a cubic yard of soil) every fall to keep it from rotting/attracting termites seems like a real pain.
Building "standard" raised beds should be a straightforward exercise in comparison.