In the Napa Valley, consumers will often ask why the vineyards are on the valley floor vs. the hillsides. There are a lot of benefits to planting on hillsides such as better drainage of rainfall, which checks the vigor of vines, and sun exposure. In fact, even in Napa Valley’s early history, the value of planting on slopes was appreciated. In Illustrations of Napa County published in 1877, George W. Gift, an editor of the Napa Valley Reporter, wrote: “Hillside exposures, facing the morning and mid-day sun, are preferred…the gravelly thin lands produce the grapes from which our best wines are made.” Today, hillside vineyards represent a small fraction of total acreage in the Valley and there are county ordinances which limit new hillside vineyard development due to erosion. But, no matter. Napa Valley has a Mediterranean climate which means a long, dry growing season. Irrigation, and vigor, is often under the control of the winegrower. At 37 degrees latitude, we also do not need the additional sun exposure that slopes provide. In fact, vine row orientation and canopy management are geared to protect the grapes from severe sunburning on west-facing fruit. During our hot growing seasons, slopes allow cool air from the mountain tops to slide down at night, slowing down the ripening process and rapid loss of acidity in the fruit.
Germany’s Mosel wine region on the other hand, at 51 degrees latitude, is historically at the northern limits of winegrowing. The best vineyards are on steep slopes facing south or southwest. At 45 degrees, south-facing slopes can deliver the same amount of solar energy than at the Equator. In cool Cote-Rotie, at the Northern end of the Rhone Valley, the best vineyards such as La Londonne are 100% steep whereas in the Mediterranean Southern Rhone, most vineyards are on a sweeping plain. In other areas like Italy where more than half of the land is mountainous, fertile plains are best allocated to agricultural crops while hardy vines thrive just as well on slopes.