Instructions
Find a flat strip of land that is seven blocks long and three blocks wide. Build a wall three blocks high around it.
Place water in the back corner of the room.
Place three sand blocks in the middle row. There needs to be one block of space between the sand blocks so the water current travels between them.
Place cactus on each of the sand blocks.
Place a row of blocks along the side of the wall. When the cactus grows, it will come in contact with the side of these blocks, which will cause it to fall off.
Stand where the water flow ends, and the cactus will be delivered straight to you.