What you'll need:
cactus mix or potting soil/sand
Since I live in Tucson, both the cactus and the soil came from my own yard. But if you live outside of the desert you will need to buy either cactus mix, which is a speciality soil or mix potting soil and sand in a 3/2 ratio.
- Pour an inch of gravel into the bottom of your cup. This will provide drainage for your cactus. You do not need to drill holes.
- Cover with a dense layer of soil. Carve out a space for the cactus sit in the soil.
- Using tongs (most people recommend gloves, but tongs have not failed me yet and once you get a spine in your gloves they are hard to get out) place your cactus into the soil.
- Use a spoon to fill in soil around cactus.
- Cover with 1/2 " of gravel.
- Water gently and ignore. Okay, not really, but cactus grow very well on their own in sun and with little water.