Don,
I follow the soil scientist Dr Elaine Ingham, both on Youtube and on the “Compost Tea” Yahoo! user group. She speaks a lot about the importance of getting air to the root zone, to maintain aerobic conditions for all of the soil microbes that drive soil fertility. In one post, Elaine Ingham recommended punching holes in the sides of a tomato grow bag, to let in the air. So, when I came across soil blocks, open to the air on 5 sides, I thought they must be ideal. I tried soil blocks for the first time last year and had enough success that I’m doing it again this season.
Peter