All you ever wanted to know about cuttings
Propagating the San Pedro from cuttings is also quite easy. All you need is a sharp knife and some soil. First, be sure that your cactus is big enough. 10" or more above the soil is a good starting point, as you want at least a 6" cutting and a 4" base. As to width, it really doesn't matter, but remember, the thinner the cacti, the quicker it will lose water. If you keep your cacti indoors, you can make a more straight cut. If you leave your cacti where they can get rained on, be sure to cut at a slant, so the rain water doesn't pool in the cut. After you have made the cut, you'll want to let both the base and the cutting heal and callous over. This should take about 2 weeks. In that time, you'll want to keep the cutting out of sunlight, and the base in lower light. After that, you can slowly reacclimate the cactus to the level of light it was previously at. As for the cutting, it's now time to plant. You should have a pot of dry soil ready. If you wish, you can dust the callous and the bottom inch or so of t he plant LIGHTLY with rooting hormone. Put the cutting about 2"deep in the soil. Wait about a week or so until you water the cutting, and then do so as normal. Soon they will put out roots, and voila, you now have two healthy, happy San Pedros.