It only takes a few minutes of reading anything about wine for soil to come into play. Whether it’s a long feature on Germany’s Mosel region, or the shelf-talker at Bevmo, experts, sommeliers, and marketers love throwing in tidbits about the ground that makes their wares extra special.
Luckily, you don’t have to go licking rocks (though some sommeliers do) to understand how fancy lingo like “clay loam” and “well-drained limestone” make grape-growing possible and the resulting wine delicious.
Soil does two things for wine. It impacts how grapes absorb (or don’t absorb) nutrients, and it provides drainage for the roots of grapevines. There are, of course, lots of other nuances that contribute to the terroir of a wine and exist in the soil, like concentrations of iron or nitrogen, for example. But when it comes to the huge difference between a vine that is thriving, versus one that’s just surviving, pH and drainage are the major players.
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Grapevines are a hardy crop, which allows them to ripen almost anywhere. But the best grapevines (and resulting wines) come from balanced vineyards, where water, nutrient, and underground Nirvana align with the sun-soaked environment above ground. The phrase “moderation in all things” applies to vineyards as well as chocolate and Netflix binges.
When it comes to drainage, that means providing vines with enough water to thrive, but not so much that the roots end up waterlogged and prone to rot or root diseases.
In winemaking, “drainage” refers to the ability of the soil to retain water. Essentially, gravelly, loose, sandy soils allow rainwater to rush away from the roots of grapevines. Clay and volcanic soils retain water, keeping it in place and available for thirsty grapevines.
For example, the stony island of Santorini, which produces some of Greece’s most famous (and most delicious) white wines, is made up primarily of hard, crumbly volcanic soil. In the dry Mediterranean, this soil retains the small amount of annual rainfall, allowing grapes to ripen. Here and in other arid regions like central Portugal, water retention is historically what allowed vines to flourish before modern irrigation systems. In wet, rot-prone areas, well-drained soils did the opposite, allowing vines to grow and preventing root diseases. Most regions combine a mix of soil types, either due to erosion or historical events like massive floods, glacial movement, or volcanic eruptions. In a moderate climate, like Napa Valley or Bordeaux, where moderate temperatures and adequate rainfall collide, that mix is a good thing.
When growers plant new vineyards, a large part of soil evaluation involves looking at drainage to determine how much water will be retained in the soil. Specific rootstocks have even been designed to grow better in well-drained and poorly-drained environments.
Once grapes have enough water, they look to the soil for other nutrients they need to thrive, like iron, nitrogen, and phosphorus. But the existence of these and other minerals in the soil doesn’t necessarily contribute to the wines, which is why pH is so important in vineyard soils.
The pH scale measures the acidity or alkalinity of a substance, and in soil that contributes to how available those nutrients are to vines. Soil pH has a huge range from three to 10 (on a scale of 14). Grapes can be grown throughout that range, but soils closer to the neutral rating of seven are preferred. These soils, coupled with adequate water, have a chemical makeup that encourages what’s called “cation,” the fancy scientific word for nutrient absorption by vines. Grape lunch, as I like to call it.
Between the pH of 5.5 and 7.0, the cation rate, or ability of grapevines to absorb the nutrients in the soil around them, increases, making more nutrients available and easily digestible for grapevines. It enables them to absorb everything they need to grow properly, rather than struggle along, like eating a healthy diet versus surviving on vending-machine fare. Some research also suggests that soils in this range allow grape berries to retain more acidity as they ripen, leading to brighter, more acidic finished wines. In Champagne, Burgundy, and Santorini, growers often attribute the finesse of their wines to the high pH found in calcium-rich soils.
Together, pH and drainage form the baseline for the success of grapevines across the world. While other factors like temperature, fertilizers, and cover crops also play a role, these simple elements remain critical.
Next time you’re in a vineyard, don’t look at the grapes, look at the ground.