Tree of the Week: The Blue Gum

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Always welcome after a week of dreary news on housing and the economy: Pieter Severynen’s ‘Tree of the Week.’ Enjoy.

The Blue Gum — Eucalyptus globulus

‘After the 1849 Gold Rush, transpacific shipping was booming. Seeds of the Australian Blue Gum Eucalyptus from Southern Victoria and Tasmania were imported in San Francisco in 1853; by 1860 the young Blue Gums had reached 50 feet. Californians started planting and hyping the incredibly fast-growing trees; thousands of newly planted acres were sold as investment property. In 1876, state Sen. Ellwood Cooper promoted their use in ‘Forest Culture and Eucalyptus Trees,’ in which he wrote about his experimental plantings near Santa Barbara. But the discovery of oil in Pennsylvania in 1859 led to the gradual replacement of wood with oil for industrial energy use. When it also became known that weed from young Blue Gum trees makes good firewood and pulp, but poor lumber because it is very difficult to cure, the instant-gratification plantation bubble burst. Still, we are left in Southern California with two thousand miles of Blue Gum hedges that protect citrus orchards from cold winds and we see thousands of older ornamental specimens in our cities.

‘The evergreen Blue Gum grows into a 50- to 160-foot-tall, 30- to 75-foot-wide tree with massive trunk and braches, impressive in stature but sloppy in foliage. Juvenile leaves are oval and silvery blue-gray; the 6- to 12-inch-long mature dark gray-green leaves hang down vertically. All leaves are so full of ethereal oils that you can actually smell the tree some distance away (but the crushed leaf smell test is fun). Small, creamy white flowers with numerous stamens appear during November–April, after the cap (Greek: eu –completely; kaluptos – cover) has fallen off the little cup that contains the flower; the subsequent almost inch-wide waxy fruit capsule is covered with a button-shaped top. Long brownish-gray strips peel off the smooth yellowish bark. Thick layers of messy leaves, seeds and bark strips congregate below the tree, prevent other plants from growing and easily catch fire. The tree has a nasty habit of occasionally dropping thick branches without any seeming provocation or warning.

‘Notoriously fire-prone because of its ethereal oils, the tree usually resprouts after a fire. It is aggressively invasive in coastal Northern California, but barely here in the Southland because our climate is too dry. Blue Gum is one of the most widely planted trees worldwide for the production of hardwood, pulp, firewood, honey, and the essential oils contained in the leaves. These are used in the manufacture of cleaners, deodorizers, food, insect repellents, and many medical purposes. For our urban forest we have far better choices available among the 600+ Eucalyptus species than the Blue Gum, although during the last 10 years many new Eucalyptus pests such as the sap-sucking, aphid-related psyllids have become established here. Thank UC for continuously introducing small predatory wasps to fight these pests the natural way.’

Thanks, Pieter.
E-mail Pieter: plseve@earthlink.net
Photo Credit: L.A. Times file photo from 2000 shows Jeff Zoumbaris, forestry services manager for Burbank, stretching his arms to show the relative diameter of a eucalyptus tree.