Encouraging native oaks

Encouraging native oaks

Few trees can claim the calm elegance of the mature black oak (Quercus kelloggii), its branches undulating at almost impossible angles from a solid base.

Equally important to the landscape and animals that share it are Oregon white oaks (Q. garryanna), which have lighter bark and more compact crowns. Beyond their beauty, the valley's oaks support a surprising number of animals, plants and bugs: grey squirrels, acorn woodpeckers, pigeons, wood ducks and deer, to name just a few.

For centuries these trees grew naturally from acorns produced each autumn, sometimes planted at a distance by birds and squirrels. Fires set by local Indian tribes, who harvested acorns for food, reduced plant competition for the fire-resistant white oak. Today, although the climate is right for oak seedlings, other factors interfere with the replacement of oak stands. But with a little effort and a regime of benign neglect, landowners can help replace our aging trees.

The Rogue Valley's oak stands often are unhealthy because people don't know their needs, says Tal Blankenship, former parks superintendent in Grants Pass. Grass, other ornamentals and extra water or fertilizer can invite disease to these trees, he says. Other problems include parked cars or other equipment that compact the soil, rototilling under the canopy and removing fallen leaves, which act as insulators from temperature spikes and return nutrients to the soil.

"They've been surviving on their own for eons," says Blankenship. "If you have natives, read up about them before you take any action."

Katie Mallams, plant pathologist with the U.S. Forest Service, is encouraging oaks to grow on her property, and she's got some help.

"If we disturb the soil, the birds will plant untold numbers of seedlings," she says. All she provides is "light, water and root space," and her efforts are being rewarded.

"They stay very small for a long time" but then growth seems to "take off," she reports. "Some of ours grow 2 feet in a year."

Mallams says she believes the early growth happens underground, when the tree sends a taproot to the water table, triggering that big growth spurt later.

According to the Oregon Oak Communities Working Group, white-oak acorns need steady moisture to germinate, and acorns probably do well under their own mulch of oak leaves, which generally fall after the acorns do.

To plant oaks, gather a good number of acorns and soak them in water for 24 hours. Discard the ones that float, which are probably host to worms. Plant the ones that sink, says Mallams.

For more advice, get on the list for the upcoming book, "Oaks in the Urban Landscape: Selection, Care and Preservation," by Larry Costello, soon to be published by the University of California. Go to http://anrcatalog.ucdavis.edu, select "join mailing list," enter your e-mail address and then select the option to be notified about oaks.

The Oregon Oaks group has an oak-care guide available for free download at www.oregonoaks.org/documents/landguide.pdf. The guide includes instructions on how to prune and thin white-oak stands.

A mature oak will reach about 70 feet here in Southern Oregon, and they can live a long time. Mallams says she visited an oak in Germany reputed to be more than a thousand years old. She says it was rotten in places and held together by bars, but it was still alive.

"Here they might not live so long."

That's all the more reason to plant them or encourage their growth, says Mallams.

"It's faith in the future. I think that is why people plant trees."

Share This Story