We know D.C. Get our free newsletter to stay in the know.

Having queried readers as to why the Inter-American Defense Board (IADB) at 16th and Euclid Streets NW paints its trees, I thought a simple phone call to IADB would reveal its motives, so I rang the department that appeared to be the most user-friendly of those offered in the phone book: the Executive of the Director. The phone was answered not by a secretary, as expected, but by a sort of Cmdr. Riker of the IADB, Col. Earl Hanson.

Still, if you got brass on the phone, you gotta be brassy and try and solve the mystery behind the mystery, namely: What is the Inter-American Defense Board? Hanson explained that IADB is a confederation of military officers that advises the Organization of American States on security issues—mostly the threat of encroaching communism.

“So whaddya do now?” I asked.

Silence. “We advise on other regional issues,” he eventually replied.

Content to leave the mystery of IADB’s role in the New World Order for another day, I turned conversation back to the trees, a topic with which Hanson was well versed. He confided that sticky tape, or burlap sacks soaked in kerosene and wrapped around the trunk, will keep burrowing critters, like gypsy-moth larvae, from climbing up the trunk and tunneling their way below the bark. He suspected the purpose of the coating on IADB’s trees was for much the same reason.

Now I don’t know what the fall of the Berlin Wall means to you. But on that day, what it meant to me was that some colonel, who a few years before would have probably been fretting over straying submarines and leftist guerrillas now had the time and inclination to quiz his staff on their gardening techniques.

Meanwhile, B. Freer Freeman of Arlington offered this theory: “An unreported spill of 29 barrels of U.S. Navy battleship gray in the basement of the IADB during the ’60s, with subsequent leakage through cracks in the building’s foundation, resulted in a below-the-surface pool of paint that ever since has been slowly wicking up the bark of nearby trees.”

Back in the real world, our other T-shirt winner, Dr. George Bean, who with a name like that could not help but be a professor of botany at the University of Maryland, e-mailed that trees are tinted white to prevent winter injury. Deciduous trees, especially fruit trees, are susceptible to fluctuating temperatures. Late-afternoon sun warms the trunks, no longer shaded by the leaves.

When the sun sets, the trunks cool rapidly—too rapidly. The resulting expansion and contraction splits the bark and damages the cambium layer of formative cells beneath.

The theory behind painting trunks is that the white pigment will reflect the sunlight and normalize temperature fluxes.

But is this practice prudent? “I would never recommend that people paint their trees,” says Kevin Carr of Guardian Tree Experts. Painting or coating trees—whether it’s for pests, or tree “wounds,” or to protect them from sunlight—is ill-advised, he says, because the paint or tar (for wounds) seals in harmful bacteria and other irritants. Painting trees is more common in Europe or South America, says Carr, and not really “U.S. accepted.” In any case, protecting trees from temperature changes is not really needed in the mid-Atlantic states, where Carr says he’s got “plenty of experience.”

Alexandria plant pathologist Dr. Neil Pelletier notes that most trees are coated to reflect car headlights—not sunlight. The latter practice was “recommended” by a horticulture text, he said, but the book offered no data on its efficacy.

Evelyn Brownlee of the National Agricultural Library unearthed a 1975 article from the Journal of the American Society of Horticultural Scientists titled “The Effect of White Latex Paint on Stone Fruit Trees.” The article noted that, while whitewashing trees (a practice the article’s footnotes indicated went back at least as far as the ’40s) had been discouraged because of paint’s toxicity, “new” latex paint was thought to reduce this problem.

“It’s a matter of personal choice,” says Helen Pepper of the Botanical Gardens. “The new thinking is that you want to plant native trees, and do as little monkeying around as possible.” In horticulture’s New World Order, says Pepper, mulching, staking, sealing, or painting trees is not recommended. As for why painted trees seem more common in Europe, Latin America, and on estate grounds, Pepper guesses that it is due to “more formal gardens, and more gardeners to do the work.” American Forests officials agree, saying that while “people of Hispanic, Mediterranean, and Caribbean cultures” often paint trees to ward off insects, if it were truly an “effective defense mechanism” trees would have evolved with white trunks.

The debate over whether coating trees is helpful continues. As to IADB’s reason for painting its trees, Col. Hanson had the final say. The trees under IADB’s command are coated with a paintlike pesticide to prevent insects from boring into the fragile trunks.

Next Week’s Mystery: Tidal Basin Mermen