Are your indoor office plants hardi cacti or tropical cacti?
There is a big difference between the two if you want to water them correctly.
Hardi cacti like the opuntia species humifusa (-45 degrees F) is native to the eastern United States; its pads ( upper photo) are bright green and its flowers are vivid yellow.
Similarly widespread but found in the West is Opuntia polyacantha ( plains prickly pear, hardy to – 25 F) . Opuntia fragilis ( to -35 F) grows throughout Canada and the West into Mexico.
You must water their sandy soil lightly.
Tropical cacti ( lower photo) are native to the rain forest regions. These prefer high humidity, warmth and rich soil. Most are epiphytes ( air plants that use trees for support but do not derive nourishment from them). You must water these foliage office plants more frequently.
Epiphyllums ( orchid cacti) produce impressive flowers in late spring.
Flowers of popular Schlumbergera truncata, from Brazil, appear in mid winter, hence the common name Christmas ( or holiday) cactus.
PDI uses both these species of cacti in our interior and exterior green foliage designs in the Andover, MA office buildings.