The Quality of Soil in our Wine Regions
It is obvious that the soil in which any plant is grown will affect the yield of that plant. So with the vine, which shares with the olive the ability to grow and even thrive, in regions that are too barren and extreme in climate for other crops. But it should not be forgotten that the soil that is visible to the eye may be only a shallow layer over something quite different: the subsoil, or layers of this, are therefore another and possibly even more important influence on a plant whose tap root will be at least 12ft (3-7 m) in length. Then there is the aspect of the vineyard, also the various sources of water. Different springs underground may water patches of ground that are close together but, because the soil through which those springs flow may be different, the effect on the roots of the vines will be different too.
In general, very rich soil is not suitable for vines, or not for those that are going to make fine wine. There are exceptions, such as in Madeira, where the soil is rich but the vines are trained high, so that market garden crops can be grown under their shelter. But sometimes, as in the port vineyards or many of the German vineyards, the vines are grown on what look like patches of broken stones, with no earth to be seen. Light-coloured soil tends to be favourable to the cultivation of vines that will yield white wines of elegance and finesse – as in the Champagne and sherry vineyards; the reflection of the sunlight from the pale soil also has an effect, as it reflects the light up on to the vines and grapes. Stones are also liked in the soil of a vineyard, because they can reflect the sun’s heat upwards, as in the Rhone Valley, and because they hold the soil beneath firmly and provide good drainage. Gravel is likewise conducive to the cultivation of vines for good wines – as witness the Graves region of Bordeaux.
Sand is good in many vineyards, because it provides a light-textured soil and vineyards wholly based on sand are protected against the Phylloxera aphid, which cannot live there. Clay by itself tends to make wines that are heavy and lacking in elegance, with a lot of body but seldom that nervous, inner acidity that is associated with breed. Chalk and limestone, which are not quite the same thing, are the light, pale soils; granite and schist are the very stony ones. Sandstone and any iron in the soil can make most interesting wines – there is a type of red sandstone called alios that is under nearly all the Pauillac region. The undulations of the subsoils in many regions, plus the very different topsoils in extensive vineyards, such as some of those in the New World, make generalisations difficult. Of course, a vine will be conditioned by the soil in which it is planted, also by the stock on to which it is grafted. But it is always valuable to see the soil of a vineyard – even feeling it can give an impression of what the vines grown there may yield.