Debbie Arrington

Seeds: Harvesting acorns for a future urban forest

So many different species of oaks inhabit our urban forest, finding pure-bred acorns can be difficult. That’s one of the complications that face Sacramento acorn harvesters.

“We don’t want to plant all sorts of interesting hybrids,” said restoration ecologist Zarah Wyly, who leads the Sacramento Tree Foundation’s annual acorn harvest. “Our biggest obstacle is finding trees that are far enough away from non-native oaks. ... It’s very hard to get perfect acorns.”

What they want are true Central Valley natives: valley, blue and interior live oaks. They’ll also harvest an occasional black oak or oracle hybrid (a desirable black/interior live oak cross).

Since oaks have a habit of pollinating with other oaks of other species, mother trees may not produce acorns that grow up to be just like them, Wyly explained.

“Oaks are very complicated – and fascinating,” she said.

During October, the foundation’s acorn gathering efforts are in full swing. Now in its fifth year, the harvester program will train about 60 new volunteers this fall. More than 200 volunteers have gone through the program and are expected to pitch in by picking up more acorns.

“We’ll have three refrigerators full of acorns,” Wyly said of her annual goal. “It’s a big effort, but we won’t take acorns we don’t use.”

The collected acorns will become oak trees for county and city parks and other open spaces, as well as along the American River Parkway and area freeways. In addition, many acorns will be part of the foundation’s Seed to Seedling education program to teach local third-graders about trees. So far, the foundation has planted about 20,000 oaks in its reforestation program, Wyly said.

Oaks – particularly the centuries-old valley oaks – are Sacramento’s most recognizable tree, but much more than symbolism motivates this reforestation drive. Oaks provide food and habitat for native wildlife. They form the backbone of our urban forest.

Despite the drought, California oaks are having a pretty good acorn year. Several local examples are keeping the squirrel population busy.

“I have a large oak tree in my backyard, which I have been told is about 300 years old,” said Joanne Mertens of Orangevale. “It provides lovely shade in the summer months, but drops something nearly year round. I have lived in my home for 10 summers now, and have gotten used to the regular droppings. But this year, it has been shedding acorns nearly nonstop.

“In past years, there were a few, but never like this,” Mertens added. “I literally have to be careful when I am out there because I may be hit on the head when one falls to the ground. The squirrels love it, but I do not.”

Depending on species, some oaks (such as valley and blue) bear acorns every autumn; others (such as the interior live oak) take two years to produce a crop. That explains part of the fluctuation.

Last year qualified as a “mast year,” an exceptionally large acorn crop. Although acorns are bountiful this fall, it’s not quite as heavy a load.

“We’re having a pretty good ‘average’ year or slightly better, but no where near as wild as a mast year,” Wyly said.

Not much is known about drought’s effects on acorn production, she noted. “There’s no scientific information because acorns aren’t considered a ‘food’ crop, so (agricultural experts) aren’t really studying it. Most of our oaks have been around a long time, so we know they’ve been through droughts before.”

According to UC Davis Arboretum superintendent emeritus Warren Roberts, oaks are being stressed by the drought.

With its 10-acre Shields Oak Grove, the arboretum is home to one of the nation’s largest oak collections with more than 100 species and about 275 individual trees.

“A lot of trees are suffering from drought basically because lawns aren’t being watered,” Roberts said. “Even though they might be drought-tolerant, oaks may be having to shift their source of water. A lot of trees are in trouble now, including some oaks.”

A tree suffering from drought stress is likely to cut down on its acorn production, Wyly added. “It takes a lot of energy to create an acorn.”

There are other hurdles to harvesting acorns.

Last week, I gathered some perfect black oak acorns that were uniformly smooth and shiny. I put them in a tin pie plate and left them on the kitchen table overnight.

The next morning, the pie plate seemed to shimmy on its own. Inside, large grubs the size of peanuts wiggled around next to the acorns, which all had newly bored holes. I screamed – and flung the pie plate’s contents to the blue jays waiting outdoors.

“Acorn weevils,” Wyly said. “They’re very common. The weevil bores into the nut and lays an egg while the acorn is still forming. The grub then eats the nut before boring its way out.

“They’re one of the main pests (of oaks). Even perfect-looking acorns can have them inside,” she added. “That’s why I always dry my acorns in the garage.”


•  The Sacramento Tree Foundation plans to harvest acorns from 9 a.m. to noon Oct. 18 and 25 at sites to be determined. If you’d like to help out, contact Zarah Wyly ( or watch for more details at


Where: Arboretum Gazebo, UC Davis campus

When: 11 a.m. Oct. 19

Admission: Free

Details: (530) 752-4880,

Take a guided tour of the arboretum’s Shields Oak Grove and learn about the many different types of oaks and acorns.