The San Pedro cactus propagates easily from cuttings with a simple sand medium. Any succulent must be allowed to form a callous on the wound (cut edge) before attempting to root. The callous forms in just a few days for smaller cuttings, while large or thick cactus cuttings may take months to properly callous over and be ready to root.
Put on protective gloves. Choose a healthy San Pedro cactus to propagate to ensure the quality of the cutting. Remove a section of the cactus with a knife or hand saw. Make the cut at an angle so rain water does not collect and rot the existing cactus.
Set the San Pedro cactus cutting in a dry, cool area away from direct sunlight. If possible, keep the cutting in a vertical position to keep roots from growing out the sides of the stalk and to keep the stalk straight while drying. Wait for the cactus cutting to form a callous on the wound. Planting now would just cause the cutting to rot in the ground.
Fill the growing pot with clean sand when the San Pedro cactus cutting has a thick callous formed. Place the cutting at least 2 inches into the sand if the cutting is small (less than 6 inches) and 3 to 4 inches deep if the cutting is larger. Support the cactus cutting between two wooden stakes with twine to keep the cutting erect. Water thoroughly and set in a bright location away from the direct light of the sun. Wait at least a month before checking for roots.
Maintain a water regimen of saturating the sand when it becomes dry but not beforehand or the cutting will rot from too much moisture. During warm weather, the watering schedule is more frequent than cooler weather.
Check for root development, after one month, by gently tugging on the San Pedro cactus cutting. Resistance means new roots are forming. Another way to know roots have formed is when the stalk begins to swell. This indicates there are roots gathering water and feeding the cactus.
Remove the wooden stakes and continue growing the San Pedro cactus until it reaches the desired height for transplanting into the garden. If you choose to keep the San Pedro cactus in a container, transplant the new cactus into your growing medium of choice and set in the house or on the patio.