Our first soil blocks.

We couldn't use the organic compost we bought because even though it
was organic, the seller couldn't prove that they had kept it at the
right temperature for the necessary time. We used dirt from our greenhouse and sifted it down through a 1/4" screen. Eliot Coleman recommends using Greensand for soil blocks, but our dirt is already high in iron, potassium, and trace minerals so we didn't use it.