If a cactus breaks off, don't throw the broken piece away. Put it into cactus soil and start a new plant. Cacti, also known as succulents, are slow-growing plants native to the Americas, and grow well without needing water. By following a few steps, it is possible to plant the broken section of the cactus that will take root and grow for years to come.
Check the broken end of the cactus. If the break is crooked or uneven, make a fresh cut to even it out.
Set the cactus piece aside allowing the cut end to callous over. The end must be dry and sealed over. The length of time it takes for the end to be calloused over varies. It depends on the humidity in the air and the thickness of the cut.
Fill a pot with cactus mix. Leave the drainage holes uncovered -- because you want the water to drain through the soil quickly. The size of the pot depends on the type of cactus you are trying to root. If the cactus is tall, then you will need a bigger pot than if it is just a small button-type cactus.
Insert the calloused end into the soil approximately 1 to 2 inches deep. Firm the soil down with your fingers to hold the cutting in place.
Place the pot in a warm, sunny window.
Water the soil thoroughly, two to four weeks later. Wait another two to four weeks before watering again. It takes two to six weeks for the roots to form.