Students always call them soil brownies, and they do look tasty!
Soil blocking, which was developed in Europe and largely popularized in the US by legendary organic farmer, Elliot Coleman, is a practice of starting seedlings in cubes of compressed soil. While Rural Studio Farm still makes use of plastic flats for starting seeds of certain crops, soil blocks eliminate the waste and expense of using plastic containers.
The blocks are made in metal molds from a mixture of soil made here on site at Rural Studio Farm, which makes them more labor-intensive to begin with—and thus might not be suitable for larger scale farms.
However, farm manager Eric has found that, overall, seeds tend to germinate and grow better in blocks, and transplanting soil blocks into the field is faster and easier than having to remove each individual seedling from its tray.
Throughout the past two weeks, tomatoes, eggplants, and peppers that were started in 2-inch soil blocks were upgraded to 4-inch blocks to allow the roots to continue to develop before being transplanted to the field once the soil has warmed up more. The 4-inch mold is made with a 2-inch cavity to accommodate such an upgrade.
There are other advantages to soil blocks. As the growing roots reach the edge of a block, they stop growing in what is called “air pruning,” as opposed to wrapping themselves about as they would in a conventional pot or cell. Indeed, as the blocks are transplanted directly into the ground, root disturbance is almost entirely eliminated, meaning that more delicate plants that cannot tolerate root disturbance can be started this way.