Cut 3- to 5-inch-long shoots off the citronella for propagating new plants. Remove the leaves from the lower half of the shoot before sticking it into the rooting soil. This prevents the leaves from rotting in the soil. Citronella produces roots more quickly when you dip the cut end of the shoot in a powdered rooting hormone, available at garden supply stores.
Cover the propagation tray with a clear plastic to create a humid environment, similar to a greenhouse. Move the tray to a warm area that receives filtered sunlight. It is important to open the cover every day to check the soil moisture and refresh the air. Mist the shoots and soil with water as needed to keep the soil moist but not wet.
The citronella shoots will produce roots in approximately four weeks. Transplant the new citronella plants into 3-inch diameter pots once the roots are approximately 1 inch long. Grow the new plants indoors in an area that receives full sunlight until the weather is appropriate to move them outdoors.