Question
Five years ago my night blooming cercus had one bloom and it opened fine and was beautiful. Last year it had one bud but it went limp before opening. This year I had two large buds, but just before they were ready to open, they went limp and did not open. What is causing this plant to produce buds that do not open. Thank you so much.

Answer
Carol,
Did you mean cereus? A type of cacti...

Nightblooming Cereus is the common name referring to a large number of flowering cereus cacti that bloom at night. Because of the short life of the flowers, the nightblooming cereus has a romanticized reputation and has given rise to erroneous beliefs, such as that the plants bloom only once a year, or only on nights when the moon is full...

If yes...You are probably letting the plant go too dry for too long when it is ready to flower...Plants drop flowers if allowed too dry out too much when flowering...

This is how I pretty much water all my plants in containers. Water your plant based on how much it weighs when thoroughly watered VS when they are ready to be watered again. Plants die from too frequent waterings, not from how much water you give them at one time. Pick the pot up and feel how heavy it is after watering it thoroughly. Don't water it again until it feels considerably lighter and the top of the soil is light in color. Some plants tolerate wet soils and others need more drying time in between...Cacti rot easily if kept too wet...

Direct sunlight (especially morning sun) is good for most plants. Cacti/succulents love light.
Clean the dead plant parts out as the appear...Hope this helps.
Rick in southern NJ