terracing & how to prep soil
New member here with a big garden project (for me). Not sure if this is the best forum, I picked 'Garden Design' on the main forum page but then it takes me to 'Landscape Design'.
I have an area about 40x40 between my barn and the fence line that I'd like to turn into a perennial (mostly) fruit & veggie garden. What I mean is blueberry, raspberry, blackberry, grapes, cherries, and some dwarf fruit trees. Along with some space for annuals and flowers too.
One problem is its sloped, about 7' vertical across the 40' span. Soil is mainly heavy clay and I dont want runoff to be a constant problem and thought I could terrace the whole thing into rows. I've went through about 5 designs and think I have a final. 6 Rows each about 6-7' wide and just a bit over a foot drop each. The two sides will be fenced with a gated arbor on each, and the row that connects them will just be a pathway. The top will be the barn and the bottom will be the property fence line. I'll do rainwater collection on the barn (1600+ sqft roof) each side into its own 330 gal container and rig up some sort of irrigation system.
So I have a couple question. First, how many years can I expect to get building the retaining walls for each row out of landscape timbers? Or is there a better material? I'd love to do it all out of rock or something more permanent but dont think I have that kind of money.
Second, the ground is clay and mostly dozed up when we built the barn... not sure how much if any is truly 'topsoil'. I was wondering for berry bushes & fruit trees how to prep the soil into something they will thrive in (or is my whole project just doomed)? I have access to unlimited amount of horse manure (a large amount already composted over the years) plus I try to compost everything I can (leaves, grass, veggies, etc). I have a tiller and could add stuff and till, just not sure how long will it take? Is it something I will have to work all year at to plant next year? Or just add the stuff, till, and be ready to plant this spring yet?
Thanks for any advice...