There are more than 500 species of eucalyptus plants, according to Cornell University. Some are little more than shrubs, while others are large, fast-growing trees. Eucalyptus trees are desirable for their strong, pleasing fragrance and medicinal properties. Some of the smaller or dwarf species are also used as landscape plants. In Australia, eucalyptus trees are famous for being the only source of food for koalas.
Geography and Climate
Eucalyptus trees are native to Australia. Today, they can be found in almost every tropical or subtropical climate in the world, according to Cornell University. These trees and plants can also be cultivated in other climates, depending on the cold-hardiness of the particular species or cultivar. In the United States, they grow best in U.S. Department of Agriculture (USDA) plant hardiness zones 7b through 10. Some species that can tolerate hot conditions will also grow in USDA zone 11.
Eucalyptus trees range widely in size and appearance. Some are small in stature, growing on multiple trunks like a shrub. Others are small trees, reaching an average height of 20 feet. Some species of eucalyptus, such as E. nitens, are among the largest trees in the world, according to California State University. Many of these trees can grow more than 300 feet tall in the wild.
Eucalyptus trees, regardless of size, have long, graceful branches. The leaves are greenish-gray or greenish-blue in color, can be round or long and slender, and are usually situated opposite each other. The wood varies from creamy white to deep brown, depending on species. All are evergreen in nature, which means they do not drop their leaves when autumn arrives.
Eucalyptus trees can grow in a wide variety of soils as long as the soil drains well, according to North Carolina State University. These trees prefer planting sites with full sun exposure and will grow quite rapidly if given enough sunlight and water. Some species, such as the red gum tree (E. camaldulensis) are tolerant of drought conditions.
Uses and Considerations
E. globulusis is a commercially important species of eucalyptus. The leaves, flowers and fruit contain essential oils that are widely used in everything from medicines to sedatives, pesticides and antibacterial ointments, according to Cornell University. E. citriodora contains citronella, which is widely used as an insect repellent. Note that while the koala has adapted to be able to consume eucalyptus leaves, most animals cannot do the same, and many species of eucalyptus are poisonous to animals, including livestock.