Maintaining George Washington's Historic Trees
By Anne Galer
Trees planted by George Washington at Mount Vernon and by his family at River Farm in Alexandria, Virginia, are now more than 200 years old. How do the arborists entrusted with the care of these historic giants maintain them in the 21st Century?
In 1783, after eight years as Commander in Chief of the Continental Army, George Washington resigned his military commission and headed back to Mount Vernon to resume his life as a farmer and landowner of more than 8,000 acres in Virginia. As part of a major redesign of the mansion's landscape in 1785, he planted trees to line the Serpentine Walk leading to the house.
Visiting today, you can still see the legacy of Washington's arboriculturall efforts. Native tulip poplars (Liriodendron tulipifera) planted by Washington stand more than 140 feet high along the green as you approach the house from the west. A tall old pecan tree (Carya illinoinensis), thought by historians to be one of the pecans given to Washington by Thomas Jefferson, provides a striking backdrop to the mansion and its view of the Potomac River. Midway down the steep slope to the river, a native chinquapin oak (Quercus muhlenbergii) breaks the descent with its massive trunk and craggy shape.
Four miles north of Mount Vernon along the George Washington Parkway is another historic site on land from one of George Washington's original five farms. River Farm is now home to the American Horticultural Society and its grounds are open to the public to enjoy the Washington-era trees and contemporary plantings that flow down to the river.
An ancient Osage orange (Maclura pomifera), believed to be a gift from Thomas Jefferson to the Washington family, adjoins the house and a large native burr oak (or bur oak, Quercus macrocarpa) and lower-standing Franklinia (Franklinia alatamaha) have provided welcome shade for generations. Foxes have made a home burrowing near the decaying trunk of one of two majestic walnuts (Juglans) dating from the time Washington owned River Farm.
More than a million visitors each year enjoy the shade and the beauty of Mount Vernon and River Farm trees, but few realize the role of arborists in preserving them. Caring for these trees, as well as helping to protect the visiting public and historic buildings from the potential dangers of any structural weakness in them, is the task of Bartlett Tree Experts at Mount Vernon and The Care of Trees at River Farm.
Each firm has a slightly different approach and a different arborist-to-client relationship, but arborists for both firms are committed to, and successful in, prolonging the lives of the historic trees that are George Washington's legacy.
Working for Mount Vernon's horticultural staff, Bartlett has responsibility for trees known to have been planted by Washington himself and uses all its resources - including its own research labs and special equipment - in the maintenance. According to Stewart Bunn, Bartlett's chief arborist for Mount Vernon, the computerized tree inventory developed by Bartlett Labs is the mainstay for managing the care and maintenance of the Mount Vernon trees. Each tree is mapped to its exact location by GPS and details of the tree's size, condition and recommendations for care are entered in the computerized database of the inventory to form the basic maintenance strategy for each tree.
The inventory not only provides an easily accessible record for all the individual specialists working on the trees, but also can produce overlays of the locations of similar trees, conditions and disease patterns for diagnostic work. For instance, when the emerald ash borer was found across the river in Maryland, the GPS tree inventory made it possible to call up not only the old ash trees near the mansion, but to locate all the ash trees on the property so that preventative imidicloprid treatments could be initiated.
Each of Washington's trees is subject to continuing visual analysis by Mount Vernon staff, using binoculars for the higher limbs. A climber-arborist inspects each tree in detail on an annual basis. To avoid unnecessary drilling that could introduce disease or weaken structure, the arborist first makes mallet soundings. Resistograph drilling is performed only for suspect areas of decay located by soundings.
Additional, sophisticated new technology that minimizes risk to the tree is also available to the Bartlett arborists. The non-invasive picus sonar can map out decay without harming the tree. Expensive and time consuming, this MRI-like technique is available for use on very valuable trees - such as Washington's 1785 tulip poplar - when it is necessary to assess condition without any risk to the tree.
During the annual inspection, according to Bunn, the arborist's findings are entered into the tree inventory and form the basis for analysis of the tree's condition and recommendations for care in the year ahead. A recent "check-up" found the need for cabling of limbs in the upper reaches of the 1785 tulip poplar, which towers above the area where visitors line up to enter the mansion. Bartlett will use lag bolts, nuts and washers to fix custom-fitted cable between the limbs.
The most important trees surrounding Mount Vernon are fitted with lightning protection. Based on new specifications developed by Bartlett researcher Dr. Tom Smiley, lightning systems are being updated to place spacers for the lightning cable farther from the trunk, install blunt tips that better attract the charge to run down the cable and, in some cases, to install fuse/breaker-like devices to document lightning strikes.
Safety for the million-plus visitors to Mount Vernon and preventing damage to historic buildings must be balanced with the great historic value of many of the trees. Although still structurally sound, nonetheless, the giant pecan has been pruned to reduce its spread on the mansion side. An old ash damaged by hurricane winds had a major section removed to save the tree and those treading beneath it.
At a recent tree-care seminar, Dean Norton, Mount Vernon's chief horticulturalist, described with great emotion the decision to remove one of the Washington-planted ash trees whose advanced decay endangered the main approach of visitors to the house. For these venerable specimens, multiple specialists may be called in to confirm the need to remove such an important part of American history.
River Farm is only a few miles away from Mount Vernon, but far removed from the throngs of tourists and extensive grounds and tree groves of Washington's mansion. Home to the nonprofit American Horticultural Society (AHS), there is a shift in both philosophy and budget evident in the approach to tree care on the 25-acre plot, but the same abiding respect for the history marked by their many old trees.
Phil Snyder is The Care of Trees' chief arborist for River Farm. He says the AHS philosophy of collaboration and building partnerships to provide learning opportunities for gardeners and horticulturalists drives a practical, less formal working relationship. The Care of Trees donates thousands of dollars a year in its work at River Farm, and finds it benefits from the exposure to expand its clientele in the neighboring area that is a significant market for the firm.
"Our basic approach is a fairly straight-forward one, acknowledging that as trees reach maturity or maximum age they slow in their overall growth and they become more vulnerable to insects, disease, wind and other physical challenges. So with that basic premise, our management of mature trees at River Farm focuses on creating as stable an environment and structures as possible."
"It's not dramatic. It involves basic care fundamentals. The key for mature trees is in maintaining as complete a canopy as possible, removing deadwood throughout the crown and canopy, supplementing available nutrients depending on the site, structural support and, as much as possible, avoiding any disruption in the critical root zone."
The Care of Trees does a visual check of the historic trees and adjacent property every several months. They scout for disease, scales, mites and a whole host of other chewing and sucking insects, says Snyder. If there are issues, they decide whether the damage threshold or health impact makes it necessary to treat. "The goal is to maintain issues at tolerable levels so that there is more impact from natural processes than our own," he says.
Part of their observation is looking for physical signs of structural challenges. The 200-plus year old Osage orange is an example of a tree with structural weakness that has benefitted from proper pruning and the addition of structural support. Thought to be grown from Osage orange seeds brought back to Thomas Jefferson from the Lewis and Clark expedition, it sits within a few feet of the historic house. The Care of Trees has installed extensive cabling and bracing to hold the tree together and protect people walking on the garden path under its limbs.
But what you see above ground is only half the story, according to Snyder. The Care of Trees places a major emphasis on root system and soil health as part of its care philosophy. "We work from the belief that urban soils typically lack organic matter that the biology of woody plants and trees need."
Because the walnuts, Osage orange and other historic trees are in an environment where they are competing with the root systems of surrounding turf, The Care of Trees' goal is to drive the fungal components that are needed to break down the organic matter, which allows a more natural nutrient recycling to occur for the woody plants. A primary part of this process, according to Snyder, is the selective use of "compost tea" to introduce biological elements to the soil to help make nutrients more available to the tree. The compost tea is applied over the trees' root systems several times a year in place of direct fertilization of nitrogen or other chemicals.
The compost tea used has been adapted to The Care of Trees' requirements by researcher Dr. Rex Bastian. It starts with selecting the right kind of compost, compost that has been carefully developed so it is dominated by the sorts of fungal and biological organisms that are suitable for a woodland-type environment. The compost is heated and aerated to multiply the living organisms and then brewed like tea. The liquid is applied directly to the soil along with some pre-treatment with fungal foods to help jumpstart the natural life cycles in the soil.
Snyder points out that because River Farm runoff drains into the Potomac and the Chesapeake Bay, the leaching of phosphates and nitrogen into the watercourses is of particular concern. "We're aware of the impact, our footprint. This is behind our using compost tea as opposed to traditional fertilization." And this philosophy fits nicely with the environmental awareness and teaching of their American Horticultural Society partners.
Two different tree companies, two somewhat different approaches for different clients, yet examples of providing long-term good needed for some of America's most historically valuable trees. Bartlett's Stuart Bunn sums up the attitudes of the arborists in both historic properties when he says, "To me, George Washington's trees are as important as the house."