The home I moved into almost 4 years ago in Shoreline belongs to folks who loved cement and asphalt. When I took the cement out of the front yard, it was laying on top of sandy loam (mostly sand) and of course, construction rubble. Took out all the rubble and added some 20 yards of booster blend--didn't see the point of buying anything with sand it it. We mixed the BB into the sand. Planted in a mix of small fruits, veggies, perennials, shrubs. Everything is quite happy.

I figured I would do the same with the back yard cement removal. Just removed 250 sq. ft. of patio. At some point they resculpted the natural slope of the back yard to create a split level with a retaining wall. The lower level is completely cemented. The new bed is in the lower level, where they did the most scooping. However, what is underneath the 5 inch slab of cement is a couple inches of extremely compacted reddish sand/subsoil and below that is god-knows-what. Alderwood till? We are removing it with a pickax. It's almost like cement. Nothing like the front yard.

Here's my new plan: take it out so there is a total of 12", loosen up what is below that with a fork as much as possible, then ill with good soil. Once I pony up the delivery fee, I figure I should get as much of whatever is needed.

Here's my questions:
1) since there is no 'native' topsoil in place here or even good sand that I can mix in with the bought soil, what would you suggest I add? Should I order a split load from Cedar Grove of part veggie garden mix or one of their sandy loam mixes and part booster blend? The only time I ever bought a 'planting mix' was from pacific topsoil and it got cement-like very quickly. So since then I've stuck with compost and booster blend and mixed it in to what is already there.

2) I had intended on putting a mix of shrubs and perennials in here--hadn't quite figured it all out yet. I'm wondering if that will work with a nearly impermeable layer that they won't be able to sink their roots into. Or will they? I cannot fathom anything growing through that stuff. Maybe I should decorate that retaining wall behind the bed rather than hide it with foundation plantings? : )

Thank you for any advice you can send my way!