Sorting through a pile of scraggly tree roots in early June, Brian Mayell conducted a quick autopsy.

“On none of these, to me, does it look like the root system was the culprit,” he said.

That’s good news for the general manager of Casey Tree Farm, who, among other duties, is charged with growing better trees for the nonprofit charged with restoring, enhancing and protecting the tree canopy of the nation’s capital, a goal it has been working toward for nearly 15 years.

“I want to make sure I send out a good root system, so the tree has a good chance of survival,” he said.

The longer the tree lives, the greater impact it has on the District of Columbia’s urban tree canopy, which Casey Trees aims to grow to cover 40 percent of the city by 2032. The nonprofit plants many of the trees in DC’s neighborhoods, schoolyards, church lawns and open spaces, while the District government concentrates on street trees.

The pioneering nonprofit is establishing best practices for planting long-lived trees that are fit for the rigors of city living — and healthy enough to do their part to filter, slow and clean rainwater that’s headed to the Chesapeake Bay.

“There’s been a heightened awareness in our urban areas (that) what we do at home is going to eventually impact the water,” said Mark Buscaino, executive director of Casey Trees, adding, “Trees play a big part in ameliorating the impacts.”

So, when the Casey family, who started the nonprofit, also donated a 730-acre farm in Virginia’s Clarke County to the cause, the nonprofit began growing something “a bit atypical for such a rural site”: city trees. Since taking over the farm in 2008, Casey Trees has transformed the property into part nursery and part experiment station, a place where the many variables that affect an urban tree’s survival can be figured out.

“A lot of times, in the toughest urban environments, there may be 10 species (of trees) that will work,” Mayell said during a tour of the farm that hugs three miles of the Shenandoah River’s shoreline near Berryville, VA. Choosing hardy species and ensuring their roots get a healthy start makes the trees more resilient against the added heat and pollution of the city.

The Casey family purchased the property, known locally as Springsbury Farm, in 1958, leaving much of its landscape in forest and leasing portions to farmers who graze animals or grow crops like corn, soybeans or hay.

Though Casey Trees now runs the entire property, it grows nursery trees on just 15 acres, separated from the rest by tall deer fences, and maintains the existing leases with farmers. Besides the nursery, the farm is home to several historic outbuildings, unoccupied horse stables and a sprawling mansion built in the mid-1790s.

“I don’t raise cows or hay,” Mayell said of the continued relationships with those farmers. He also is not keen on giving tours of the mansion. “I grow trees.”

From river bottom to city streets

If there is a problem with using this farm as an experiment station for the city, it’s this: “Everything does great here,” Mayell said.

“Underneath, there is smooth, river bottom soil,” he said, pointing down the sloping hill where hundreds of trees leafed bright shades of green from plenty of rain in early June.

In the city, these trees will face all sorts of obstacles. In that environment, “if you could make 80 percent of your trees grow for 15 years, that would be a huge success,” Mayell said.

To that end, Mayell considers having an in-house nursery to be an advantage. Growing its own trees allows the organization to hone in on the best practices for every stage of the tree’s life. The farm also focuses on growing trees that are rarely found at commercial nurseries or are more cost-effective to grow themselves.

Casey Trees planted its first nursery trees in 2011, allowing two to five years for most species to grow before transplanting them to the city. The nursery currently grows about half of the 2,500 trees that Casey Trees plants each year in and around the city — the rest is purchased from other nurseries.

Casey Tree Farm doesn’t grow the trees from seed but purchases “liner” trees from companies that do, saving the nonprofit about three years of growing time on the front end. At the nursery, Mayell and his crew of four watch them closely, taking notes on the planting and growing methods that appear to work best.

When a tree dies in the city, Casey Trees’ crews send its root system back to the farm so Mayell can take a closer look. A lack of water is still a main cause of death for trees —though likely not this summer, which saw record rainfall in June — but sometimes a knobby set of stunted roots from a restrictive burlap bag could be to blame.

Anna Mische John, a gardener from the U.S. Botanical Gardens, who was interested in the farm’s work and also visited the farm, talked shop with Mayell about best practices for tree planting — balled-and-burlapped or bare root?

About two-thirds of what Casey Trees plants is sent to the field in fabric bags rather than balled-and-burlapped. Mayell said that’s because the “B-and-B” trees can weigh four times as much as the bagged trees and be too difficult for volunteers to plant.

He noted that Casey Trees is also interested in restoration work, like a project they did in Rock Creek Park with the National Park Service. He showed Mische John 200 or so trees left on a tarp, leftovers from a batch of 1,500 that were part of restoration work, and held up a small shrub with a cone-shaped root ball that mirrored the container it was grown in, and which, unlike other containers, directed the roots vertically rather than horizontally.

“Maybe it’s an advantage in a place where you’re not going to go back and water,” he said of the unnaturally deep roots. But “I don’t think this container works well for us.”

Other experiments have worked out well, and could slowly change the way the organization — and perhaps the broader industry — plants trees.

Mayell is currently working to grow bare-rooted trees in widely available mulch rather than gravel, which can be more costly and too acidic for some trees if it comes from the Shenandoah Valley.

His personal goal is to grow trees that aren’t as high-maintenance; they can be planted along a highway or in a yard and “not be taped or need to be protected from deer browsing.”

Sometimes the way to get more trees into the city is to grow smaller ones.

“We are focused on growing the urban tree canopy, but there is a need for small trees,” Mayell said. “People don’t have the space for an oak or elm, we’ll do a redbud or a dogwood instead.”

In the end, every tree counts.