Did Thomas Jefferson's efforts to grow wine grapes fail due to disease or a climate that was far colder than today's?

The answer is probably a little of both.

Over 56 years, beginning six years before he wrote the Declaration of Independence, continuing during his term as third U.S. president, and until his death in 1826, Jefferson tried to grow dozens of species of wine grape vines.

He never produced a single bottle.

It was a disappointment to Jefferson as both a wine-lover, with tastes that grew even more refined during his time as ambassador to France, and as an unabashed advocate of the New World's agricultural potential. Jefferson's journals detail his experiments with hundreds of plants, many aimed at proving America had a climate for farming that could rival Europe's. And he also sought an alternative for Virginia to the single crop on which its economy was based, the soil-leaching tobacco.

'Noble' wines, with a catch

But the classic European wine grape species, Vitis vinifera, which produces all the so-called "noble" varieties of wine, is highly susceptible to a North American plant pest called phylloxera, an aphid-like insect. Native American grape species (Concord and Catawba, for example) have a natural resistance to phylloxera, but they produce a wine that didn't appeal to most colonists and that wine enthusiasts today often describe as "foxy," tasting like it is made from fox grapes.

Disease-resistant American plants would eventually become crucial to the world's continued enjoyment of the familiar vinifera varieties – Merlot, Cabernet, Chardonnay, Pinot Noir, Sauvignon Blanc and others. Trade and ship transport over the Atlantic Ocean eventually brought the phylloxera blight to Europe's shores, and around 1860 it nearly wiped out the French wine industry. But winegrowers discovered they could combat the blight by grafting European vines onto resistant Native American rootstock. Today, wine grapes around the world are protected from phylloxera by such grafting.

Most wine experts and Monticello's own website cite phylloxera as a probable cause for Jefferson's viticulture failure. But biographer John Hailman, author of the 2009 book, "Thomas Jefferson and Wine," casts doubt on whether grafting could have saved Jefferson's crops. Hailman cites Jefferson's gardening records showing that his vines died a number of times due to deep freezes, and at least one June hailstorm.

Concrete evidence

Jefferson's 18th-century refrigerator called the 'Ice House.'Jefferson's 18th-century refrigerator called the 'Ice House.' (Photo: Marianne Lavelle)

Gabriele Rausse, the current groundskeeper of Monticello, believes there's concrete evidence of early Virginia's relatively cold climate under the Jefferson home's North Terrace. That's where visitors to Monticello can peer into the remnants of an innovative 16-foot-wide-and-deep "Ice House" that Jefferson himself designed (above). This 18th-century refrigerator was cooled with ice cut from the frozen Rivanna River in the valley below. The blocks were hauled up to Jefferson's mountaintop retreat in a caravan that sometimes numbered more than 60 wagons. But in the 38 years Rausse has lived near Charlottesville, he has never seen the Rivanna freeze once.

Still, Rausse is quick to note that Jefferson also appeared to enjoy extraordinarily warm years too, succeeding at least once in growing almonds. "That means to me he had a winter that was very warm, because almonds bloom in February," Rausse said.

Jefferson himself kept weather observation journals, including twice-daily readings to mark what he judged to be the temperature lows and highs.

There are complications in using that record to compare the temperatures of his time to today's, said Michael Mann, meteorology professor at Pennsylvania State University, who specializes in past climate reconstruction. Jefferson took his thermometer indoors at least part of the time – a practice that would affect readings – and packed it along with him when he traveled to Paris and Philadelphia.

Jefferson's notes about the weather in Monticello. Jefferson's notes about the weather in Monticello. (Photo: Marianne Lavelle

Founding father observations

But one of Mann's graduate students was able to show evidence of climate change in another set of founding-father weather observation records. The journals of Jefferson's friend and fellow Virginia plantation owner James Madison correlate with tree ring data in showing that the summer peak of rainfall shifted from Madison's time to today to about one month later, from May to June.

There's more abundant evidence that the Old Dominion's climate has warmed in more recent decades. The Chesapeake Bay, which borders Virginia on the east, has not frozen over since 1977, but did with some regularity as recently as the early 19th and 20th centuries, according to the Chesapeake Bay Foundation. The U.S. Geological Survey this month published research showing that the air temperature in the Chesapeake Bay region increased 2 degrees Fahrenheit and the water temperature, 2.5 degrees, from 1960 to 2010

Tony Wolf, viticulture researcher and professor at Virginia Tech University, said he believes the records of that era, including Jefferson's own 1785 book, "Notes on the State of Virginia," make clear that cold weather was one of the factors that hindered efforts to grow European wine grapes. "I was amazed to read some of the accounts of the Chesapeake Bay freezing over, and the thickness of the ice in the rivers," he said. "It was a very cold period. And Jefferson was trying to grow grapes that we know were very cold-tender. When we look back and see how they failed, it's really not too much of a surprise."

Hailman wrote that despite Jefferson's trials in growing grapes, the founding father never gave up his belief that the U.S. would be a great wine-making country. The dream may not have been misguided since Rausse and other vintners have steadily made Virginia into the vanguard of states investing in expanding wine production. These wine-makers have responded to global wine challenges—like climate change—with hybrid grapes and shifts in vine cultivation practices to produce wines that have begun to receive the notice of wine aficionados and experts alike.

"Jefferson was, in this area as in so many others," Hailman wrote, "simply much ahead of his time."

The Daily Climate is an independent, foundation-funded news service covering energy, the environment and climate change. This story was originally written by Marianne Lavelle for The Daily Climate and is republished with permission here.