Taking the Cutting
To take a stem cutting from a night-blooming cereus, use a new razor blade to cut a stem at a natural joint. Most night-blooming cereus stems are fairly long, measuring up to 15 inches. A shorter segment of stem measuring 2 to 4 inches will also root, as long as the stem is cut at a joint. Make the cut at a slight slant to remind you which is the bottom of the stem, and to provide a larger rooting area.
Developing a Callus
Allowing the stem to develop a callus is critical; otherwise the stem may rot once planted in soil. Dip the cut end of the stem cutting in a powdered fungicide, which is an additional way to prevent rot. Place the stem in a dry place for seven to 10 days, or until the cut end forms a firm callus.
Preparing for Planting
Fill a container with a gritty potting mix that has been slightly moistened ahead of time. A commercial potting soil for cactus and succulents works well, but a handful of sand will improve drainage capacity. Roll the callused end of the stem in rooting hormone powder, then plant the stem in the soil. While rooting hormone powder isn't required, the hormones increase the chance of successful rooting.
Planting the Cutting
Plant the bottom 1/2 inch of the night-blooming cereus stem cutting in the container. Install a stick in the pot, then tie the stem to the stick to hold the stem upright. Water the stem cutting very sparingly whenever the potting mixture feels slightly dry. Never water excessively. The cutting should take root in four to six weeks. Give the plant ample time to develop a healthy root system, and don't transplant the cutting into a different container for at least four to six months.