A bottlebrush plant is any member of the Callistemon genus, which has 34 species. They are so-named for their narrow, cylindrical flowers that resemble brushes used to clean bottles. Most bottlebrush plants are native to the temperate areas of Australia and can only grow outdoors in USDA hardiness zones 8b and higher. These plants are typically slow-growing from seed, so cuttings are usually the best way to propagate them.
Fill a pot with a soilless medium. Prepare the medium froml a mixture of about 40 percent perlite and 60 percent peat. Add enough water to keep the medium moist but not wet. The precise mixture is not critical, as long as it's kept moist.
Take a cutting of a mature bottlebrush plant in the spring or summer. Cut a shoot from a half-ripe stem that's up to 3 inches long. Cut the shoot off at the stem to get the entire heel. This is the part of the shoot that widens out as it joins the stem.
Plant the bottlebrush cutting. Place the cutting in the pot with the cut end in the growing medium and cover it with a plastic bag. Secure the bag with a rubber band to keep the moisture from escaping. Put the pot in a spot with indirect sun or fluorescent lighting.
Repot the bottlebrush plant once it becomes established. Use a pot with a diameter that's large enough hold the mature plant. This can vary considerably, so you'll need to know the adult size of your particular species.
Mix a potting soil that consists of two parts humus, one part perlite and one part garden soil. Transfer the bottlebrush plant to the new pot and fill it in with your potting soil. Water the plant thoroughly and allow it to become fairly dry before you water it again.