Maybe you don't just want a cactus that truly looks like a regular houseplant. Perhaps instead you want to crochet something with more character. Enter Sally the Cactus. Sally is a really simple crochet cactus pattern that comes alive thanks to the addition of cute eyes and blushing cheeks.
Of course, you could actually use the same pattern to crochet a very simple cactus without the face on it as well. The design includes a crochet pot (as opposed to "planting" your cactus in a store-bought pot). It is worked in single crochet and half double crochet stitches with some use of the back loop only technique.