Minecraft wiki entry for Cactus_farming, associated text: Notice how each cactus is only next to 1 piston and each piston except on the edges is next to 4 cacti. When building, make sure it is same if you want to use the least pistons. The first time you build this, it may be helpful to place the sand and pistons first. You could do this on a level surface, digging an extra block lower for each piston. When you are satisfied that the placement of the pistons is correct, remove the sand and ground where the redstone goes.