The best and most efficient cactus farm design for Minecraft would be an automatic farm. Here's a simplified step-by-step guide: 1. Build a sand platform: Set up a grid with sand blocks. Each block should be with a gap of one block between each other. This is where the cactus will be planted. 2. Plant the Cactus: On top of each sand block, plant a cactus. Be careful not to touch it as it might hurt you. 3. Building the frame: Above the first sand block, build a frame with any block of choice leaving two blocks for the cactus to grow. This frame will allow the cactus to drop once grown. 4. Water current: Place water at one end of the channel to generate a current that will lead to the collecting point. 5. Collection point: Use hoppers at the end of the channel to collect the cactus and direct them into a chest. Remember that cactuses break when a block is placed next to them hence this automatic design, where the frame block forces the cactus piece to drop off when it grows. Also keep in mind that cactus can only be planted on sand. The bigger you make your farm, the more output you'll have. Happy farming!