The cactus called good luck cactus is also known as Euphorbia trigona. Its name may originate from its easy-to-care-for requirements, or its green color often associated with luck and fortune. It is a succulent plant and has few care needs. It is also known as African milk tree, for its milky sap.
Make sure your good luck cactus is in a good location for it to thrive. It likes plenty of indirect sun, but not full direct sun, as it has a tendency to burn when overexposed.
Check its soil. Good luck cacti like soil that drains water away quickly, with mostly sand, possibly mixed with smooth stones, pumice or grit. A dense or moist soil will result in the cactus rotting.
Add a small amount of fertilizer diluted in water in the spring to jump-start new growth, but do not add it any other time of year. Good luck cactus is slow-growing and can easily be over-fertilized.
Water infrequently. Once every two to three weeks should be sufficient during its growth cycle, and during its dormant phase it does not need watering at all. When in doubt, don't water. The soil should be completely dry before watering.
Keep the cactus warm. Its optimal temperature is about 55 degrees Fahrenheit. It is a desert plant and does not survive in lengthy cold conditions. Keep it in a place where the temperature is not going to dip below 40 degrees Fahrenheit or so. Even a few hours with freezing temperatures will kill Euphorbia trigona.
You can root new good luck cacti easily in the spring. Cut pieces of the original cactus and place them in loose sand. Wear gloves and take care, as the sap is poisonous and irritating to the skin.