Rainbow eucalyptus is one of nature's coolest trees showing off a rainbow of colors on the entire trunk and major branches above. Its growth rate is in the range of 5-8 feet per year to reach 220 ft. The trunk will get thick fast and may become 6-8 feet wide. The heartwood is red and is used as a timber and ornamental wood. It soaks up a lot of water, making the wood very dense.