The area of Stellenbosch, because of its diverse variety of terroir, has fondly become known in South Africa as the ‘Kingdom of Cabernet’. Due to its array of soil, which amounts to as many 50 different types, winemakers in this region have been able to produce some of South Africa’s top Cabernet examples.
The Stellenbosch region is made up of several different soil types, predominantly a mix of red and yellow-brown Tukulu and Oakleaf soils, as well as structured Swartland, Klapmuts and duplex Kroonstad soils. They are acidic with decomposed granite onthe mountainside vineyards and alluvial soils on clay bases in the valleys. The Stellenbosch soils, at altitudes of 150-600m are on steep slopes and are relics of a high rainfall, tropical area from millions of years ago.
The geological history of the Cape’s winelands began 540 – 245 million years ago with formation of the supercontinent Pangea. With the subsequent fragmentation of this supercontinent and the creation of the Cape Fold Belt 245 – 63 million years ago, the southern African landmass was then subjected to a virtually uninterrupted process of surface erosion under varying conditions and with considerable changes in sea level.
The effect of this not only changed the landscape, it caused the rocks of the area to be chemically altered, weathering to depths greater than 10 metres. This depleted the fresh minerals in the soil material derived from this weathered parent material.
As a result of these activities, South Africa not only has among the oldest viticultural soils worldwide, they are among the poorest or least fertile, a fact which works in Cabernet Sauvignon’s favour.
Geology of Stellenbosch
The underlying geology of the Stellenbosch district includes rocks of the Cape Granite Suite, the Malmesbury shale Group, the Table Mountain Sandstone Group and recent unconsolidated sediments of Quaternary age. Generally, the sandstones and quartzites of the Peninsula Formation, Table Mountain Group are found in the highest reaches while the young unconsolidated sands are found in low-lying lands close to the coastline and adjacent to riverbeds. The older and more erodible geology of the Cape Granite Suite and the Malmesbury Group are generally found in the lower part of the landscape or form lower hills.
Most of the soils of Stellenbosch’s vineyards derived from the Cape Granite Suite and Table Mountain Group, but there is also some influence from the shale of the Tygerberg Formation, Malmesbury Group.
More about Stellenbosch Soils
Soils derived from granite are usually found on mountain foothill slopes and ranges of hills, are red to yellow in colour, acidic and with good physical and water-retention properties. Oakleaf, Tukulu, Hutton and Clovelly soils are included in this group.
Soils derived from sandstones of the Table Mountain Group are generally sandy with low nutrient and water-retention properties, for example, Fernwood, Longlands, Westleigh, Dundee soils. There are also important pockets of shale-derived soils which include Glenrosa, Swartland, Klapmuts and Estcourt soils. These are usually brownish, strongly structured, on partly decomposed parent rock, with good nutrient reserves and water-retention properties.
Another feature of the vineyards is the absence or presence of Koffieklip (ferricrete), an iron-rich sedimentary rock. Soil particles are cemented together by iron oxides (such as Fe2O3) precipitated from groundwater during water level fluctuations to form a hard erosion-resistant layer.
These soils types can be found across all Stellenbosch’s wards, being derived from the Cape Granite Suite and Table Mountain Groups. However, there is considerable variation in the forms the soils take, and most forms can be found on every property.