Cedar trees don't make the soil acid. At least not appreciably so.

Be cautious about your planting process. You don't want to damage a large portion of the cedar roots.

Thanks for the info- a couple of different garden centers told me about the acidity problem: I did a soil test and it wasn't overly acidic, but I trusted them.
I am thinking of building raised beds back there, or working some containers in: do you think covering the ground there will harm the trees?