Original species have stood the test of time and still sell well, while new smaller columnar hybrids of Quercus are coming on strong

With fossils found as old as 55 million years, oaks have been entwined with human history since it began. Because of their longevity and massive proportions, the largest oak species in the Fagaceae family enjoy a near-epic reputation. Sayings like “strong as an oak” and “from tiny acorns mighty trees grow” hint at our awe for them.

Oaks remain popular across the United States today, from coast to coast.

In McMinnville, Tennessee, a grand white oak (Quercus alba) has welcomed passersby for over 250 years. A landmark since 2000, the so-named “Birthing Tree” stands 81 feet tall and has a crown over 130 feet wide. The tree gained stature as a meeting place and shelter for settlers on the Old Kentucky Trail. Some pioneer women, while waiting for their companions and supplies or a storm to clear, gave birth to the next generation under its branches. In 2015, American Heritage Trees collected seeds from the Birthing Tree to perpetuate its next generations.

Across the country, in McMinnville, Oregon, is Robinson Nursery. Adam McClanahan, Robinson’s national field representative, marvels how trees — oaks in particular — connect us to history.

“A mature white oak is my favorite oak overall,” McClanahan said. “My family knows I will slam on the brakes while driving if I see a mature white or bur oak.” He said he visits a Q. alba specimen, probably 50 feet tall and wide, that graces a local cemetery, where he thinks about what the tree may have seen in its time. “Wow, if that tree could talk, I’d sit and listen.”

McClanahan also cited the environmental benefits oaks offer when building natural landscapes. Native plants attract pollinators and need the filtered shade oaks provide. Oaks offer humans, birds, deer, squirrels and other wildlife protection and nourishment.

“Not only in woodlands for wildlife, larger oaks provide coverage for the understory plants that need to grow,” he said.

But what’s the appeal of oaks for nurseries? “Just the diversity in sizes and shapes, as well as where they can be used,” McClanahan said. “It’s a broad family of trees that can carry over from multiple soils and climates.”

Species appeal

“There are species applicable to every climate in North America,” said Marc McCormack, chief sales officer at Bailey Nurseries. Some hybrids eventually edge out the species in popularity, but oak species have staying power.

“I was counting the oaks we grow at Bailey, and it’s something like 20 or 25 total,” McCormack said. “But what I find interesting, unlike some other trees, like maples and ash, we still sell 12 different species.”
While there have been cultivars introduced from Q. alba or Q. rubra, market interest in true species remains solid. Bailey Nurseries grows oaks from bare root to 25-gallon containers and 2-inch calipers. “We rarely have years we don’t sell through our oak inventory,” McCormack said.

“Oak is the backdrop of the landscape,” said Alan Heinrich, vice president of horticulture for Everde Growers in Orange, California. With 15 farms across the country, Everde carries 11 oak species.

“Our most popular is the holly oak,” Heinrich said. “That’s the one landscapers’ plant.” Other bestsellers include Q. agrifolia, the California live oak; Q. suber, the famed “cork oak” which offers rugged bark and thrives in cool, wet springs and hot summers; and Q. virginiana, the live oak, an excellent hardwood that supplied the nation’s first publicly owned timber for Navy ships.

Oaks for smaller homes

Most people don’t have the space for a 50-foot-wide tree in their yard. But now oaks come in columnar, upright, compact varieties that have become wildly popular along with the market for smaller-profile trees and shrubs.

“The fastigiate ones, we cannot grow enough,” McClanahan said. With homeowners living in smaller lots these days, he said, “They are looking for something in that family of plants, but they don’t have room for a plant that gets 40 feet wide.”

Wholesale grower J. Frank Schmidt & Son Co. (JFS) has bred several columnar oak hybrids. “Oaks are very promiscuous,” said Guy Meacham, JFS product development manager. “There are thousands of oak hybrids from species from different parts of the world that hybridize together, and you get very good plants from those. Even though you’re starting with parents from different parts of the world, they often bring the best character of both.”

When making selections, Meacham said, breeders look for new and improved benefits. In the case of Crimson Spire™ oak (Q. × bimundorum ‘Crimschmidt’), the original hybrid of North American Q. alba and European Q. robur bred by JFS, its benefit was having foliage “that looks good all year long in the city rather than getting covered in mildew.”

Launched more than 30 years ago, Crimson Spire has become a classic. Its leaves turn rusty red in fall and hold color well; they also stay on the tree until new ones emerge in spring, which is great for screening.
For those who prefer a clean look in winter, there’s Streetspire® oak (Q. × bimundorum ‘JFS-KW1QX’), which drops its leaves in fall. Both Crimson Spire and Streetspire average about 45–50 feet high and spread about 15 feet.

The narrowest of JFS’s English white oak hybrids, the aptly named Skinny Genes® (Q. × bimundorum ‘JFS-KW2QX’ PP 24442), has glossy green leaves that persist after turning yellow in fall.

“The bicolor, swamp white oaks are very useful in the industry, especially for planting in cities,” Meacham said. He recommended American® Dream for a traditional spreading silhouette at 50 feet high by 40 feet wide or Beacon® oak for an upright form that only reaches 15 feet wide.

For even tighter spaces, Kindred Spirit® hybrid oak (Quercus × warei ‘Nadler’ PP17604) is a cross between upright English and swamp white oak that grows 35 feet tall and only 6 feet across. “That is my hands-down favorite,” McClanahan said. “I like the color, size, everything about it. It has a nice orange fall color because of the English oak parentage.” Depending on the alkalinity of the soil, he said, it can vary in color from maroon to more yellow.

No pressure

When it comes to pest and disease pressure, oaks are relatively easy on the grower compared to some species.

“Quercus is pretty bulletproof,” Heinrich said. “Some oaks are susceptible to twig or leaf galls, but with proper timing of our insecticide we can control those. There are some borers, like clear ring borers, from time to time but we scout for them.”

However, oaks do have a habit of growing sideways. “One of the problems with oaks is their root systems,” said Shawn Nerison, vice preseident of Surface Nursery. “They like to run a big taproot, and it’s not uncommon for the root to take off sideways right off the bat and that’s not good.”

To keep the plant’s roots growing on the straight and narrow, Nerison said each plant seed is grow in a tube in the greenhouse for its first year, and that’s not all. “After they’ve been underground a year, we undercut them.” In this process, a machine cuts off about a third of the root system to encourage more fibrous roots for easier transplanting.

Sometimes, a tree will grow its own, unbalanced way. “Some can be difficult to get to branch evenly so we do special pruning,” Nerison said.

Everde also takes preventative measures to head off issues. “We take a lot of pride in our root pruning process,” Heinrich said. Any kinked or spiraling roots are pruned before planting in a new container.
“It might take 30 to 50 years to girdle the trunk, possibly felling the tree,” Heinrich said, “but it’s an investment in the future for our customers.”

With all their upright trees, Everde prunes the canopies for strong dominant leaders, eliminating weak branch angles, ultimately saving time and money in pruning for the first 5­–10 years.

Next wave oaks

Looking ahead, Meacham at JFS foresees strong interest in two areas. “There’s probably more interest in fastigiate or narrow oak trees just because of space limitation, and there’s more interest in people in having more regional oaks, that are perhaps more specifically suited to their areas.”

For example, Gambel oak (Q. gambelii) and its hybrids are on the upswing, Meacham said, especially in places like the Southwest, where “it’s adapted to that xeric climate.”

There may also be a greater need for dry-adapted trees elsewhere overall. “We will be looking for tougher oaks that don’t require as much water and have good ornamental qualities,” Meacham said.

For the moment, Everde is sticking with species — but that may change. “We are looking at our own selections and own genetics, but we haven’t rolled it out yet,” Heinrich said.

Bailey Nurseries works with several breeders to create improved crosses and varieties with marketable attributes like compact form. “We’re always looking for disease resistance,” McCormack said. Others are selected for improved fall color, cold hardiness and alkaline tolerance.

“Certainly, if we could ask for anything it’s that they could grow a little faster,” McCormack joked. “But it’s certainly fun to watch them grow in popularity.”

From the April 2023 issue of Digger magazine | Download PDF