Use this ingenious gadget to turn your potting compost into little blocks in which to raise seedlings. The blocks are composed entirely of compost & have no walls as such. Instead of the plants' roots circling as they do upon reaching the wall of a container, they fill the block to the edges & grow no further, the narrow air spaces between the blocks keeping the roots from growing from one block to another. Large blocker makes 4 48mm (2) blocks at a time.