In preparation for planting, I had already cleaned off a long bed and had removed lots of old vine and roots from between all the small chunks of lava. We used chainsaw to create 2-foot long segments of the old log as a border for one end.
Today, I thought I was ready to plant, but as I began to dig out holes for the one-gallon plants, I found there was yet another layer of lava about 6-8' down that had been covered by lots of small broken pieces left from the original clearing for the house and driveway. Anyway, I used the pickaxe to break through the "crust" that was about 3-4" thick. Below that was a wonderful mix of earthworms, and soil!!! What a great surprise for our new plants -- "Jock's Cairn" is the variety.