Choose a stem that has several leaf or bud nodes from which the plant can produce future stems. The stem should also have a few leaves.
Cut the stem well below the bud node. Your cutting should be at least 6 inches long.
Place your cutting in a small clear container, such as a baby food jar. Fill with water. The plant will release rooting hormone and the less water in the container the stronger concentration of rooting hormone. You can also place more than one cutting per container.
Plant cuttings when they have produced roots that are least 1/2-inch long.
In the fall, or at least four months before you expect the last spring frost, fill growing containers with a sterile, well-drained soil.
Sprinkle the begonia seeds on top of the soil and gently press them into the growing medium but do not cover. Begonia seeds are extremely tiny; you may want to mix the seeds with sand to assure even distribution.
Mist the seeds enough that the soil around the begonia seeds is moist but not waterlogged. Place the growing containers on a large tray. Begonia seedlings must be watered from the bottom to prevent fungal disease.
Place your begonia seeds in front of a sunny window or under a grow lamp. Begonias need light to germinate.
Mist daily. Begonia seeds require high humidity. You could also place a piece of flat glass or plastic over the growing container to create a mini-greenhouse effect. Keep the soil temperature between 70 and 75 degrees F and your begonia plants should sprout in 14 to 20 days.