Tree of the Week: Holly oaks make good street trees

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The holly oak (holm oak) -- Quercus ilex

Holm is an old English word for holly. Leaves, especially young ones, of this evergreen tree may have spiny pointed lobes and resemble holly leaves. At first glance this tree looks like our coast live oak, but it is denser, more grayish green, and it lacks the open grace of our native tree. Holly oak is one of more than 500 species of oaks occurring in the Northern Hemisphere. It is native to the Mediterranean Sea basin, where different populations valued it for distinctive reasons: The Romans made cartwheels and tools from the hard dense wood, the Greeks used the leaves in predicting the future and creating honorary crowns for people of distinction, and the Spaniards fed the acorns to their pigs. The tree has become naturalized in several areas where it was introduced, including along the West Coast.

The holly oak is a moderate grower. Eventually it may reach 30 to 60 feet tall and wide, unless its round-headed shape is altered by pruning as in the accompanying photograph. Branches look somewhat stiff; the gray bark is rather smooth. Variable shape, shiny leathery, 1-to-3-inch-long leaves are usually oval to lance-shaped, smooth and darker green above, fuzzy and gray below. They may be spiky or smooth along the edge.

Green catkin flowers, with males and females on the same tree, eventually produce 1-to-1.5-inch-long gray-brown acorns, deep set in their cups. Long lived, resistant to pollution and drought, able to take hard pruning and grow in various soils, the holly oak makes a good street tree. It will tolerate salt air and semi-shade, but it prefers full sun. Occasional problems include caterpillars, powdery mildew, scale and oak root fungus.

The holly oak is a member of the Fagaceae (oak or beech family).

-- Pieter Severynen

Thoughts? Comments?