The Geology and Major Soil Types of Bordeaux

  • By Jacky Blisson MW
  • 21 Nov 2020
  • 5 MIN
  • Level 201
Made possible by
Vignes Medoc - Credit : CVM

Vines need soil to grow and to produce fruit. At the most basic level, soil is necessary to anchor the plant in place. How well a soil holds water determines how much moisture the plant will receive. Similarly, the mineral composition of a soil governs the vine’s nutrition. Soil temperature can also be a major factor in fruit ripening speed. As each wine grape variety has different requirements, matching the right soil type and grape variety is key to achieving healthy, high quality wine grapes.

Overview of Bordeaux Soil Types

Bordeaux is a large wine-producing area with just over 110,000 hectares of vines. The region is split in two by the Gironde estuary which is formed by the joining of two rivers: the Garonne and the Dordogne. The vineyards to the east of the Gironde and Garonne are referred to as the Left Bank. This encompasses the Médoc, Haut-Médoc, and Graves regions. The area to the west of the Gironde and the Dordogne river, is called the Right Bank. The famed Saint-Émilion and Pomerol vineyards are found here. In between the two rivers, before they form the estuary, is the Entre-Deux-Mers, where over 50% of Bordeaux’s wine is produced. 

Vineyard soils vary widely throughout the region, but are largely composed of gravel, sand, clay, and limestone. While pockets of gravel can be found on the Right Bank and clay-rich soils exist across the Left Bank, gravel features more prominently on the Left Bank and clay-limestone is more common on the Right Bank. Similarly, in the Entre-Deux-Mers there are many soil variations including some gravel and sand, but soils are typically cooler with deep clays and clay limestone being predominant

Clay-Limestone Soils

Origin

Limestone, a sedimentary rock, is basically the fused and solidified skeletal remains of ancient marine organisms. This forms the bedrock of much of Bordeaux’s vineyard area and was laid down during the Tertiary period. Clay, a fine-grained soil material typically made up of particles of weathered rock, overlays limestone in many of the Right Bank’s finest vineyards.  

Key Soil Attributes

The Conseil Interprofessionnel du Vin de Bordeaux (CIVB) divides the clay-limestone soils of Bordeaux into slope soils and plateau soils. 

Bordeaux’s clay-limestone slope soils are quite shallow. They are composed of a thin top layer of limestone gravel, with clay subsoils mixed with varying quantities of silt and sand. They are soils that generally warm up quickly upon the onset of warmer spring weather, inducing early budbreak and ripening. Clay-limestone slope soils have limited water holding capacity but are good at regulating water supply to the vine. They are relatively infertile and generally produce medium yields of small, concentrated grapes.

The clay-limestone plateau soils have variable depths, some reaching down as deep as 140cm. These soils have high clay, silt, and sand content over their limestone bedrock. How early they warm in the spring and ripen crops in the fall depends largely upon the location of the vineyards. Areas facing south and west are warmer and ripen fruit earlier than those sites facing north and west. Soil fertility is also variable depending on the vineyard situation. The high clay levels give these soils high water retaining properties. Yields tend to be moderate in size.

Where Are These Soils Found?

  • Clay-limestone slope soils: Saint Émilion and its satellite vineyards, Fronsac, Blaye, Castillon & Francs Côtes de Bordeaux, pockets of Pessac-Léognan, the Médoc, and the Haut-Médoc. 
  • Harder clay-limestone plateau soils: Saint Émilion, Fronsac, Castillon & Francs Côtes de Bordeaux, Barsac, Blaye, and parts of the Entre-Deux-Mers (around Grézillac), the southern part of the Graves appellation, and Margaux.

Which Grapes Grow Best In These Soils?

  • Merlot, Cabernet Franc, and certain white grape varieties in the Graves and Entre-Deux Mers areas.

Gravel Soils

Origin

The famous gravel soils of the Left Bank are alluvial in nature, meaning that these sediments were carried along the river networks of Bordeaux and deposited on their banks. They originate largely from the Pyrenees mountains and the Massif Central alternatively, eroded during glacial periods of the Quaternary period.

Key Soil Attributes

Bordeaux’s sandy-gravel soils can reach depths of ten metres in certain areas. They have gravel topsoil, with subsoils of sand, silt, and clay in varying proportions. These soils warm quickly in the spring. The gravel layer aids with ripening by reflecting sunshine back up into the vine leaves and fruit, and by retaining heat to radiate back into the vines at night. Gravel soils are relatively infertile and very free draining, two conditions which foster deep rooting of the plant. They tend to produce low yields of small, thick-skinned, flavourful grapes. 

Where Are These Soils Found?

  • Médoc, Haut-Médoc and its crus, Graves, Sauternes, pockets of Saint-Émilion, Pomerol, Lalande-de-Pomerol, and in the Entre-Deux-Mers near Cadillac. 

Which Grapes Grow Best In These Soils?

  • Late-ripening varieties like Cabernet Sauvignon and Petit Verdot.

 

 

 

Vignes Medoc - Credit : CVM