Soil, the factory floor of every vineyard, is much misunderstood. Read a few back labels, look at a few websites, and if you believe what you read, the wine in that bottle and the different wines coming from whichever producer owns that website will all taste the way they taste just because of the soil they are growing in. This is of course true, but only partially true. There are many other factors in play.
As a viticulturalist helping people plant vines in England and Wales and dealing with lots of different sites with soils of different types, and different pH levels, I know that choice of rootstock (just one of the several decisions that affect the style, flavour and quality of a wine) is possibly more important than the soil the vine’s roots are growing in. Remember, it’s not your Chardonnay, your Pinot Noir or your Bacchus whose roots are actually touching the soil, but the rootstock your vines are grafted onto. And I would also contend that other parameters such as vine density (how many vines are planted per hectare), pruning style, yield and canopy management are probably more important than soil in determining a wine’s style and quality. Add to that list the vineyard’s quality – its altitude, aspect and slope – and you can see that it is obvious that soil can only be one factor in a wine’s makeup.
So how does soil affect wine? What role does it play in the vineyard? Well of course it’s where the vine lives and where it anchors itself. It’s where it gathers the water, whether falling naturally or supplied via irrigation, that it needs to grow. It is where roots have access to the minerals a vine needs to produce chlorophyll, the essential element needed for photosynthesis to occur.
The one thing that is highly improbable is that ‘minerals’ are somehow extracted from the soil by the vine’s roots and absorbed by the vine, ending up in the grapes, and thus into the wine.
I remember well a Master of Wine tasting of Champagnes, hosted by four producers, two grand marque houses, and two smaller producers, one of whom ventured the notion that the taste of minerality in his wines was because the roots of his vines had wrapped themselves around the large flints in his vineyard and physically sucked the silica out! If roots had the power to do that, then growers could just spread silica (or whatever mineral had shown itself to be beneficial in flavouring the grapes) onto the soil and let the magic begin.
Of course it’s very lucky that roots cannot behave in this way when you think of growers who spread manure of animal origin on their fields who would be horrified if their wines smelt or tasted of cow, sheep or pig’s dung. If we forget vines for a moment, and think of other foods and drinks that we happily consume and enjoy, and whose flavour and taste we appreciate, how many make a fuss about the soil they grow in? Take root vegetables for instance – such as carrots, potatoes, or parsnips – none of which go through the very flavour-converting process of fermentation – how many are promoted or advertised as ‘tasting of the Fens’ or ‘tasting of Scotland’? Answer: none.
Alex Maltman, Emeritus Professor of Earth sciences at Aberystwyth University, and who has a special interest in wine, has written the well-received book Vineyards, Rocks and Soils: A Wine Lover’s Guide to Geology in which he thoroughly debunks the idea that minerals can actually flavour wine.
Whatever the chemical make-up of your soil, vines don’t take up more nutrients than they need. Why would they? Excess leads to problems as we know if too much fertiliser is spread. Having said all of the above, it is now time to acknowledge what influence soil can have upon a vine’s growth and how the way a vine grows can play a part in its style, flavour, quality, and of course, quantity.
Soil not only comes in many different types and compositions, it also comes in many different layers in terms of depth and spread. Dig say a two-meter-deep soil pit in one spot and you may see three distinct layers of soil – top soil, sub-soil, and sub-solum, each of which can be measured. Dig a pit a few metres away, and you may only see one or two layers, each much deeper or shallower than in the first pit.
In short, unless we can see underground, which of course we cannot, soil sampling, soil pits and even soil scanning with an electromagnetic device, has to make assumptions about the depth of soil in any one place in order to divide the soil up into meaningful sectors.
The structure of the soil is also an important factor in how a vine establishes and grows. Having planted vines on many different types of soil over the last 50 years, the major difference between soils is the speed at which the vines initially spread their roots and grow and establish a trunk and cane. Take loamy sands or even heavy clay, especially soils which have been in cereals, grassland or fruit orchards for many years. These usually have plenty of organic matter in them, allowing roots to access minerals and water and spread their roots quickly and as wide and as deep as they need to.
Sites like this, with good management, and good weed control, can quite often produce fruit in year two. Sites with a moderately high stone or gravel content, which often have excellent drainage, can also establish quickly and successfully.
My experiences with what might loosely be called ‘chalky soils’ i.e. those with pure chalk sometimes very near the surface, lots of flints of various sizes, with high pH levels, low nutrient status and low organic matter, are often slow to establish and can take at least three years (and often four) before a modest crop is produced. Of course much depends on the vine management both before planting and during the establishment phase.
Neglect to get the pre-planting soil preparation right, especially drainage, and your vines will struggle. Neglect to single them down to one bud shortly after they start sprouting, and you can add another year (or even two) before they start cropping. Let weeds grow unchecked and your beautiful new vines will struggle as the water and nutrients they need to grow roots and establish a good root system will be stolen by those pesky weeds. Don’t believe that ‘leaving them alone’ (what might be called neglecting them) makes vines resilient and able to cope with whatever nature throws at them. It doesn’t. It weakens them and kills them.
You have to remember that a vine is not a sentient being. It cannot think for itself. It can of course react to its surroundings, and we know what too little or too much water and too low or too high a temperature (to take two very basic parameters in the growth cycle) does to a vine. A vine’s job is to grow canes, produce fruit that is sweet so that its seeds are attractive and spread by birds and animals, thus perpetuating the species. As we know from hydroponics, plants, even vines, do not need soil as long as they have light, water and the right nutrients, plus the right temperature for the variety. A vine’s roots, the method by which they access most of the water and nutrients they need, will only dig downwards as far as they need to. Provide them with water on the surface, and their root spread will be quite limited, one of the problems associated with irrigated vines. They also only need enough nutrients for shoots and leaves to grow so that photosynthesis can take place. We also know that whilst the right nutrients (and the right amount of those nutrients) are needed to produce chlorophyll, a vine will not normally take up more nutrients than it needs. In dry regions, where irrigation is not used, a vine may grow a deep, even a very deep root system, but the nutrients it needs may be in the upper reaches of that system where nutrients, produced when plant matter breaks down, are more plentiful or where they have been spread. Generally speaking, the deeper you dig in a soil, the less nutrients you will find, and plants are lazy by nature and will only dig as far as they have or need to.
Having established good, economically sustainable vineyards in many different soils, my advice is that if a soil needs drainage, then drain it, if it needs subsoiling, then subsoil it, if it needs nutrients and/or lime, then add them, if it lacks humus, then add it, or plant cover crops if you have time. Whatever you do, don’t think that doing nothing is necessarily the right thing to do. Neglect never produced a good vineyard.
Rootstocks
Given that pretty well all vines grown commercially in the world are grafted onto phylloxera-resistant rootstocks, and that these rootstocks in many instances play an important part in how the vine interacts with the soil its growing in, its surprising how little importance some sections of the wine industry give them.
How often do back labels and website blurb reference the rootstock used? Not nearly as often as the soil type the roots are growing in. Rootstocks have the ability to root deeply or less deep; to provide vigour in low-nutrient soils; or to help control vigour in higher vigour soils (such as we often find in GB). They are also necessary to cope with the stresses and strains of growing vines on sites with high active calcium carbonate levels, where iron chlorosis is an ever-present threat.
To my way of thinking, getting the right rootstock for your soil and for your vines is one of the most important factors in producing good grapes.
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