Sonoma County landscaper discovers new species of blue oak along the Silverado Trail

Luke Dexter had driven the same stretch of the Silverado Trail for a decade, not noticing anything strange, until one day five years ago when a strange oak caught his eye.

After that, he couldn’t avert his eyes. He found himself turning his head to take a look every time he passed the tree on his way to and from his office in Calistoga.

It appeared to be a native blue oak, or Quercus douglasii, like the other oaks growing around it along the side of the road. But this tree was different. It was much smaller than the other blue oaks around it.

It is stubby and growing up like a bush. It has characteristics of a witch’s broom, which is a dense mass of shoots growing from a single point in a tree. It is an aberration, and looks much like a broom or bird’s nest. Dexter believes his tree is not a witch’s broom, but a genetic mutation that has dwarfed the tree.

“By 2016, I was convinced that its slow growth rate and exceptionally dense growth habit was something special,” he said.

Dexter works for Dexter Estate Landscapes, a high-end landscape installation company based in Calistoga founded by his father, Dave, in 1985. The company has installed many high-profile projects in Wine Country, including Stone Edge Farm Estate Vineyards and Rams Gate Winery, both in Sonoma.

One of his strengths is in siting and setting trees. His eye is trained to notice trees in a landscape. He figures that is why he was able to pick out a single tree as one-off, even in a quick drive-by.

But Dexter said his fascination with trees goes beyond his work. It started when he was a boy, growing up in Sebastopol. His father, Dave Dexter, who has a degree in botany from Sonoma State University, collects rare Japanese maples. The younger Dexter started taking cuttings and potting them. He now has an impressive collection of more than 100 rare Japanese maples growing on his 1½-acre property in Angwin. He also has magnolias and oaks . “This is my obsession,” he said.

Dexter might have just left it as a literal passing fancy. But by chance one day he stumbled on a documentary about “the miracle manzanita,” a variety thought to be extinct in the wild. Daniel Gluesenkamp, director of habitat protection and restoration for the Audubon Canyon Ranch in Marin County, noticed the elusive Franciscan manzanita as he was driving along Doyle Drive in The Presidio 10 years ago. Some trees and shrubs had recently been removed in preparation for a major road improvement project, bringing the rare lone tree out into full view. But it was in the path of the new road.

If Gluesenberg hadn’t spotted it and saved it, the tree would have been doomed. Since then the Arctostaphylos franciscana, known to grow only natively in San Francisco, has been removed and replanted. Botanists are now attempting to help it reproduce with others of its species that had been protected in parks and botanical gardens in the Bay Area.

That story of rescue inspired Dexter to take action about the mysterious tree in the Napa Valley that had captivated him for five years.

“My goal is to introduce this new and unique tree to the world,” he said.

Dexter joined a Facebook group called International Oaks. Almost immediately after posting a video of himself with the unusual dwarf oak growing on county property along the side of the road. He heard back from Ryan Russell, a member of the board of the International Oak Society, who is in charge of registering new cultivars. Russell responded that he had never seen anything like it.

“I’ve only seen it in photos. But from the photos it looks like a genetic dwarf, which is pretty rare in oaks,” said Russell, who now has some cuttings and is attempting to grow them at his home in Columbia, Missouri.

The one-of-a-kind oak tree has been named Quercus douglasii ‘Dexter’s Blue’ in recognition of the man who found it. Dexter is now attempting to select it out and cultivate it to share with other tree collectors and possibly for introduction into the market.

“My goal is not to have them at Home Depot and garden centers. My goal is to make them available to passionate collectors and other people who want to be able to obtain one.”

He has sent scions to Heritage Seedlings in Oregon, one of the nation’s largest growers of small tree starts, including oaks and conifer. Blue oak don’t do well planted directly. So the cuttings have been grafted onto Quercus macrocarpa rootstock. Heritage has 89 in their greenhouses. Dexter has also sent cuttings to Pat McCracken in North Carolina, one of the East Coast’s most respected grafters.

“We grafted them about two weeks ago. It will be quite awhile before we know what they’re doing and a month or so before we see if they’re putting out buds. But I could tell from the wood it sent it looks very dwarfed,” McCracken said.

“From the picture he sent, it is intriguing. It looks like it would make a nice small landscape plant.”

The out-of-state growers are somewhat challenged because Quercus douglassii is native only to California. The bark is light gray with medium-sized dark cracks that from a distance can make it appear almost white. The leaves have a dark blue-green tint, hence the popular name of blue oak.

Right now Dexter is in a waiting mode to see what happens to his baby trees. The International Oak Society needs to make sure that the trees that grow from the scions maintain the same habit. If they grow out, they should be a perfect clone to the parent tree near Calistoga, an attractive oak that would be nicely sized for smaller landscapes and yards.

“I had baby twins, a boy and girl, in February of last year,” Dexter said. “My grafts of this tree are the exact same age. They are part of something special to me. I’ll be able to plant them at our place and they will all be able to grow up together.”

You can reach Staff Writer Meg McConahey at meg.mcconahey@pressdemocrat.com or 707-521-5204.

Author Talk and Garden Pop-Up

Who: Lauri Kranz and Dean Kuiper, authors of “A Garden Can Be Anywhere.”

When: Noon Today

Highlights: Author talk, book signing and tea. Flatland Flower Farm of Sebastopol will create a pop-up garden in the courtyard of the shop for the weekend.

Where: The Miracle Plum in Railroad Square

Address: 208 Davis St., Santa Rosa

Information: miracleplum.com.