The Willamette Valley, Oregon’s coolest winegrowing region, is the source for most of Oregon’s wine grapes. The Willamette Valley is by far western Oregon’s largest winegrowing region in size, vineyard acreage, and number of wineries.
In January 1984, the Bureau of Alcohol, Tobacco and Firearms (BATF) formally recognized the Willamette Valley as a designated viticultural area. Approximately 170 miles long and 60 miles wide at its greatest breadth, the Willamette Valley viticultural area covers 5, 200 square miles. Forming an elongated “V” narrowing to the south, the Willamette Valley runs from Oregon’s northern border on the Columbia north of Portland to the Calapooya Mountains south of the city of Eugene, half way down to the state.
Once a submerged inland bay, sediment and lava flows gradually filled the bay, slowly raising its floor above sea level to create today’s Willamette Valley. The process began in the southern Willamette, the most inland part of the bay, and worked its way northward.
Bordered on the west by the Coast Range Mountains and on the east by the foothills of the Cascade Mountain Range, the Willamette Valley is a mosaic of prairie, open savanna with scattered oak trees, grasslands, and forest and woodlands of Oregon white oak and fir trees. Except for a slight extension into southwest Washington, the Willamette Valley vegetation pattern is unique in the Northwest.
Willamette Valley vineyards are located on wooded hillsides in the western part of the valley, along the foothills of the Coast Range; on the slopes of the valley’s volcanic hills; or, on the many hillsides that have been eroded into the basalt lave plain during the last 20 million years or so.
The Willamette Valley viticultural area generally extends no higher than 1000 feet into the foothills of the surrounding mountain ranges. Willamette Valley winegrowers have found that southerly hillside slopes between 300 feet and 1, 000 feet elevation make the best growing sites.
Higher slopes are too cool and rainy. Lower slopes risk frost hazards. Nighttime cool air settles in lower elevations, and the vines do not warm as rapidly to the summer sun. Not only does cool air pool on the valley floor, but the heavier moist soils are slow to warm, and delay vine growth in spring. The heavier soils on the valley floor also produce more vegetative growth, delaying grape ripening. The relatively flat valley floor makes up much of the Willamette Valley, but the land is not well suited to grape growing.
In this northern marine climate, southerly hillside slopes capture the most energy from the sun. Parts of the Willamette Valley are subject to frequent, morning, low clouds, a reminder that the Pacific Ocean is not far away, and that the Coast Range Mountains only partially block the onshore flow of marine air.
Winter freezing is almost never a problem for the Willamette Valley’s temperate climate. For the better vineyard sites, frost is an infrequent problem, but on less than ideal growing sites, such as those at very high elevations or on the valley floor, spring frosts are a concern. Rain is moderate during the summer months, but increases in fall and winter, and often aggravates the grape harvest.
The Willamette Valley climate is classified as Region I, the coolest of the five heat regions in the U.C. Davis classification system.
Information provided courtesy of Willamette Valley Vineyards, Turner, Oregon
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