Tutorials/Cactus farming

Cactus Farming is the systematic planting and subsequent harvesting of cacti. Cactus farms are useful for acquiring green dye, by smelting of the cactus blocks. Interesting, effective and large farming configurations can be achieved by using creative structuring of water source blocks and sand. Cactus growth is achieved on blocks of sand and with an absence of adjacent blocks next to the plants.

Tiered Cactus Rows
If there is space available above a 1 or 2 block high cactus, but there is a block next to where the new cactus block will be, then the cactus will grow and immediately break off, dropping a cactus resource around its base. Water flows can then be used to move the drops from many planted cacti to a single collection point. The trick is to place the "breaker" block along the same row as the cactus, so that it forces the dropped cactus block into the water. Highly efficient cactus farms can be generated using tiered rows and waterfalls, as seen below.

You may also put a Torch to prevent freezing in a snowy or freeze-prone biome. Keep in mind that some of the cactus drops can be destroyed by the cactus block.

Pedestal Cactus Farming
With this method of cactus farming, you can harvest cacti without taking damage by using a platform and a water canal for the cactus blocks. First, look for a 12x12 square and begin with a line of 7 sand blocks. After that, build a footing with Cobblestone or any other block you like and surround the sand line. Then, build another layer with Cobblestone so you can reach the second level of a grown cactus so you can hit them easily. Lastly, get a bucket with water and pour out the water in the middle of the sluice. Wait for the cactus to grow up and break the upper block while standing on the pedestal. With this method of farming you gain about 85% of the cactus blocks.

Piston pushing base block
Pistons can be set in a place where when they activate, the pushing end is adjacent to the base block of the cacti, causing it and the above blocks to break.

Piston pushing an adjacent block
This is a very simple design, with pistons below the gravel blocks. When the cactus has fully grown, activating the pistons will then push the gravel blocks up, which will break all the adjacent cacti blocks. This is very effective when it comes to harvesting it as cacti yield is 100% with no loss, though it requires you to replant them. This design is also very easily expandable.

And when you are done harvesting, contracting the piston blocks will also allow the gravel to fall. Hence this design does not require any sticky pistons.

Piston pushing middle block
Another method is to setup pistons to push the middle cactus block, breaking the top two blocks. This allows the third, bottom block to remain that replanting is not necessary. Note that cacti will not render as many blocks and is potentially less efficient due to losing blocks in the process, similar to stepping on tilled dirt with seeds growing and losing the seedlings.

Automatic Harvesting
The concept behind this is done with the setup outlined above, except when constructing your building you need to place blocks two spaces above the sand, adjacent to (but not touching the sand) so that they float in the air. The reason behind this is that when cactus comes in contact with an adjacent block it will auto-shed the segment of cactus touching it. This way, when the cactus grows to its 3rd segment high, your floating block will be adjacent to the cactus, so the top piece will break and fall into the water.

Some notes about this though:
 * When a collectable block touches a cactus it will be destroyed. So sometimes when it auto-sheds itself the collectable cactus block will fall onto living cactus and destroy itself.
 * It may be more beneficial to place the block high enough so that when the 2nd segment attempts to grow it harvests itself. This reduces the waiting period of growth in the initial planting.
 * You want to minimize the number of possible points of contact for a cactus block to make contact and fall back to the living cactus. Using the dense checkerboard pattern, consider using iron bars or glass panes and placing them with the bars/panes separated by 3 spaces on the cardinal direction and 1 space on the ordinal direction. This ceiling pattern ensures that all cactus are only being touched on one side, and minimally so (2 pixels), giving the block plenty of room to escape.
 * It is also possible to make a transport system for the cactus if you place a single water source in the corner of the 'box' you constructed for the farm. When placing the water block, you need to place it on the 2nd block above the ground to create a 'down fall' of water which then produces the required force to allow the water to reach the farthest corner away from the source block. With this setup it is possible to have the newly harvested cactus blocks float to a single collection point.
 * Try to experiment with wooden pressure plates at the collection point. Set up a redstone torch which stops burning when the pressure plate is pressed down by a cactus block.
 * The block adjacent to the top cactus can be a sign rather than a solid block.

Multilevel Farming
Automatic farms can be stacked on top of each other to increase yield.

Using a design like this, you can create insanely large and space efficient cactus farms. Also, with some water, hoppers, and a chest, you can make it fully autonomous leaving it, and collecting the cactus later.

Video
Ackerbau/Kaktusfarm Tutoriels/Cultiver des cactus Кактусовая ферма