I hate to be flipant but it seems like theres a lot of hipe over a simple 2 foot retaining wall going on here. I have bult many retaining walls up to 8 feet high with everything from rock to timbers and 2 feet just isnt that big. You dont need engeneers or anything. The Keystone type blocks that are designed for such a thing would work great. 6X6 tibers would also be great with "Deadmen" every 6 or 8 feet. A deadman is a timber layed under the actual load bearing surface that ties into the wall. Like a T in the wall. You lay down the first course of wall on well compacted gravel atleast 6 inches or more deep with a good drainage direction. Then you rebar that,or the next course with it, in to the ground with 3 or 4 foot rebar.You lay the deadmen perpandicular to the wall and 6 or 8 feet long. You spike rebar them in at the wall and under the parking pad. Add a course and offset the next set of deadmen. Rinse and repeat. Make sure its all well compacted. IF you want you can set each course of the wall bacl a half inch to create a backward lean into the load area. Make sure it drains and your in buisness. Railroad ties are lame and environmentally unsound. If you want to use 3/16 steel put Upright pipes in concrete every 2 feet and 4 to 5 feet deep. You can also create steel or wood deadmen to weld or bolt to the retaining wall. I would think 6x6 treated timbers would be better but if steel is cheaper for you and yop can weld then just make it bomb proof with 2 or 3" Posts in concrete and deadmen to prevent flex. Good luck, hope all goes well.

So the overgrown bushes, and especially their roots, must have soaked up and slowed down the water so that your patio stayed dry before, huh? Sorry to be a downer, but I'd be surprised if there is anything you could do with bricks and plants that would stop the water from coming down any time soon. Maybe eventually the plants might develop enough roots to do the job, but if it's going to be a veggie garden it doesn't seem to me that you would get enough. Installing drainage tile behind the base of the wall would work, but that's a ton of work, and would probably mean rebuilding the wall. I get tired just thinking about it. You could try digging down a foot like you were thinking and then lay the drain tile in that trench, covering it with small stones and landscape fabric. That might intercept enough surface water to do what you need. Good luck. ThinMan

You will need to dig down so that the bottom of the wall (which is the bottom of the footing) is below the frost line. Maybe a regional forum could help you find out what frost depth is. A footing is like a nice thick sidewalk that is created for the wall to sit on. (8" thickness depth would be good. 6" might be OK.) You're building a retaining wall so keep in mind that it needs to be sturdier than a free-standing wall. A footing ought to protrude beyond the footprint of the wall itself, by about 8" all the way around. So that's a total width of 24". If the present excavation only allows for the wall, you would need to excavate farther into the hill, also allowing for the space occupied by the form work. The wall will not look good if the block slopes. Instead, it should be level and to control it's height, step it down with level changes as needed. The footing would step down, too, as needed, in 8" increments (or multiples thereof) to accommodate the block courses. You'll need to use wire mesh in between courses of block. For heft and strength, I would fill the cells of the block solid with concrete as it's built. (Retaining walls that are under built tip over with time. Also, you will need to embed rebar into the footing which turns upward into the wall itself, locking the two together and helping the wall to last. Search Google images for "CMU wall" and you'll be able to see all manner of examples and details. My instructions are general and you must reconcile them with local conditions.

I was considering the cleared area at the top of the wall for Lewisia; some Lewisia plants will slowly form a mat via the hen-and-chick process, other Lewisia plants may remain a single rosette of leaves. If you want to put them in a more vertical part of the wall, you would need a quite wide pocket or crevice to transplant the size of plants typically found for sale. If you can get seeds, those could be started in quite narrow crevices; the seedlings often bloom in year 3. Lewisias would take a very long time to disguise large rocks. If planted on a horizontal surface, place a shallow layer of small gravel just below the leaves; otherwise soil, weeds or grass might contribute to the plants rotting out.