Here is a picture of a tomato plant in a soil block. A soil block is just what it sounds like; a block of soil. The reason we plant this way is for a smoother transplant. We find that when we grow seedlings in little containers the roots get all wound up. When they grow to the edge of the container they just start circling the inside and form a big clump of roots. With soil blocks the roots grow to the edge of the soil block and meet with the air. This causes them to stop growing outward and develop more root shoots rather than longer ones. Then when we do put them in the ground, all of the roots that grew to the edge of the block just start right back up again and continue into the soil. It's easy to loose a couple of weeks worth of growing to a bad transplant. We've found that using soil blocks can eliminate any transplant shock if it is done right. The trick is using the right recipe for the blocks though. If they are too hard the plants wont grow, if they are too soft they fall apart. We use about a 2:1 ratio of peat moss to compost plus some other ingredients. That seems to work pretty well. It's basically a slight variation of Eliot Coleman's formula.