One Big Pokey Cactus can be processed into 2 Big Pokey Cactus Seeds each without requiring any crafting recipe. These Seeds can then be planted on tilled land or on Dirt, Grass or Mud to grow into more Big Pokey Cactuses.
Grown Big Pokey Cactuses can be used in the Cooking Station to cook a wide range of Food. Food can be consumed by player characters to be granted many different buffs (positive effects) and also fed to Pets so that they can then be harvested from.
Seeds cannot be eaten by player characters or Pets directly.
You can grow Crops like Big Pokey Cactus from Big Pokey Cactus Seeds on tilled blocks of Dirt, Grass or Mud or on (non-tilled) Dirt, Grass or Mud. First place such natural blocks over a body of Water or Mineral Water, or alternatively place these liquids directly adjacent to each such block (like directly below for example, or at least corner to corner).
This can even be done underground in complete darkness and/or in a building, but not at too high altitudes, not in too cold nor too hot Biomes/layers, and not too close to Swamplands or pools of Bog Water. In these cases, Seeds will stay "fallow" and won't grow (they can be picked up again though).
Next place the Seeds on the suitable blocks next to the liquid (just like you'd place any block). If you want to use tilled land, you need to first craft a Plow and use it on the solid blocks to till them. You can, but you do not need to fertilize Seeds in order to make your Crops grow faster.
Crops can be harvested by being "pulled" with the gauntlet and left mouse button (by default) just like any other type of block, item, plant or liquid. If Big Pokey Cactuses stay "ripe" for 20 RL hours, they will turn into "grown" Crops. The harvest will become a little less then, but Crops won't wither.