A Christmas cactus can be propagated in soil by taking a leaf cuttings or a branch cutting and inserting it into a pot of potting soil. The cutting should be at least 2 inches long and have at least 2 sets of leaves. Place the cutting in the pot and cover with soil, making sure the cutting is secure in the soil. Water the cutting generously and then keep it in a warm, humid environment with plenty of bright, indirect light. After a few weeks, you should see roots starting to form. Once the roots are well-established, you can transplant the cutting into a larger pot.