Regular cacti grow best in alkaline soil, according to the University of Rhode Island. If necessary, add lime to raise the pH of the soil.
Christmas cactus (Schlumbergera bridgesi), Easter cactus (S. gaertneri) and Thanksgiving cactus (S. truncatus) are all plants that grow in tropical tree crotches. These plants need fertile, acidic soil, with a pH of 5.5 to 6.2, according to Texas A&M.
You can buy easy-to-use pH meters at hardware stores and garden centers. In addition, your local state or county extension service may offer inexpensive soil analyses.
If the stems or leaves on your plant turn yellow, or the plant fails to thrive despite adequate care, test the soil pH. PH that's too high or low affects the plant's ability to absorb nutrients from the soil.