Bottlebrush plants (Callistemon spp.) get their name from the spikes of flowers that bloom at the ends of the stems, bearing a strong resemblance to a bottle brush. Grow them as shrubs or small trees that grow up to 15 feet. Most bottlebrush varieties bloom over a long summer season in shades of red or crimson. One exception is C. sieberi, which has light yellow flower spikes. Bottlebrush plants need a very mild climate. If you live in an area cooler than USDA plant hardiness zones 8b through 11, grow bottlebrush in pots that you can move to a protected area for winter. Use a rich, peaty potting soil with a few handfuls of sand added to improve the drainage. If pruned hard every year, the plants will grow in pots as small as 6 to 8 inches in diameter. If you plan to let the shrub grow, you’ll need a large tub.