Dry, Dry and Dry Again
'Dry Farming' somehow sounds like an impossible aim when you think that all plants need water to grow, but it doesn't actually mean growing vines in the desert. It's a term that you often see attached to new world wines where growers rely simply on nature's whims for enough rainfall to grow their vines, rather than using additional irrigation as has become the norm in so many new world countries.
Grapevines are generally pretty tough plants and can produce a crop in some very unforgiving, rocky dry landscapes where nothing much else will grow. Think of the precipitous slate slopes of the Mosel; the stony 'galets' of the Rhône; the sun-baked terraces of Croatia's Dalmatian coast or the well-drained gravels of the Médoc.
Even weeds find it hard to grow in these places but vines can give top-quality results when forced to struggle. To be slightly anthropomorphic, grapevines like a cushy life – so if they have lots of water, they will tend to put on lots of leaf and don't bother to grow deep roots.
It's only when they perceive they may die that effort goes more into rooting deep for water, then reproduction and seeds – which for us means grapes. Luckily in most of these places – at least for now – there is enough rainfall and soil moisture to keep vines going, so in reality 'dry farming' is still typical in Europe.
The effects of climate change on viticulture
It may not be the case for long though, as warming climates and droughts make viable viticulture more challenging. France and Spain have eased restrictions on irrigation and since 2013, even Italy has allowed emergency irrigation for vine survival purposes in its top DOC and DOCG sites.
Grapevines are typically grown in what are described as 'Mediterranean' climates, with plenty of summer sunshine and relatively low summer rainfall, which coincides with the maximum water needs of the vine. It's been calculated that vines need more than 600 mm of annual rainfall – though this will also depend on the soil type (for instance clay stores water better than sand); how densely planted the vineyard is; evapotranspiration (in breezy, sunny climates moisture evaporates much more quickly – think laundry on the washing line on a good drying day) and even aspects like rootstock and grape variety as some are more drought tolerant than others.
It also depends on when the rain falls – for instance it has been calculated that Tuscany typically has around 200mm of rain in the growing season while Napa in contrast only has 60mm, while parts of Chile see almost no summer rainfall at all.
Grapevines spend the winter dormant then water demand goes up as the season progresses. Around 35% of water needs are from fruit set to veraison (the point when berries change colour and start ripening) then 36% from veraison to harvest.
Without sufficient water, all sorts of things go wrong – such as poor flowering, uneven fruit set, small berries, leaves yellowing and dying, fruit shrivelling and even death of the vines. The ripening process may stop altogether when lack of water means photosynthesis shuts down so you get green flavours, poor colour and lower quality. This is clearly detrimental to producing a commercial crop, never mind a quality one, so irrigation has become standard practice where climate does not allow for growing grapes without help.
So let’s have a quick look at the options for irrigation. Historically – even going back to ancient Egypt and still in use in parts of Argentina and Chile today – grape growers used flood or furrow irrigation, where water is simply allowed to flow down furrows between the vines. The problem is that this is quite a wasteful process and rather uncontrollable.
In Australia, flood irrigation was also often used pre-1960s then overhead sprinklers became widespread. By the 1980s, worries about availability of irrigation water saw the introduction of drip systems that use up to 50% less water and deliver moisture close to the vine trunk where it is of most benefit. It also helps reduce fungal disease as the leaves and fruit zone stay dry.
Then in the 1990s, even more technical approaches were developed such as regulated deficit irrigation (RDI). This aims to keep vines with just a little bit of drought stress at the right time to mimic the ‘struggle’ that so many European regions do naturally. RDI can be used to keep leafy growth and shoot length under control, to limit berry size to increase colour and concentration, especially in red grapes.
A further variant of deficit irrigation is partial rootzone drying or PRD. This requires two lines of irrigation pipe (so more expensive to install) but the idea is to keep one side of the vine’s roots dry so it moves into drought survival mode with benefits in lower yield, better colour and concentration, then the other side gets enough water to keep the vine healthy. It uses even less water than RDI too.
…and the inevitable down sides
Ironically all these lower water use approaches have made the problem of salinity worse in Australia’s vineyards, as potentially toxic salt accumulates around the vine roots and has to be washed or ‘leached’ away in the winter.
Another factor to consider is that water comes with a financial cost – one recent paper reckons that 87% of Australia’s vineyards are irrigated and that water currently costs 3,000 Australian dollars per megalitre. On top of that, there are electricity costs to pump the water around and infrastructure like piping to pay for too.
In California, John Williams of Frog’s Leap is a strong supporter of dry farming. He points out:
'For more than a century, all grapes grown in the Napa Valley were dry-farmed. Indeed, all of the great and fundamental wines that established the reputation of the Napa Valley: the great early wines of Beaulieu and Inglenook, the wines of Stag's Leap and Chateau Montelena that won the Paris Tasting, the ground-breaking wines of Mondavi, and on and on – each and every one from a dry-farmed vineyard.'
He explains that irrigation really first arrived for frost protection (overhead sprinklers can work really well to protect young buds against spring frost damage) but caught on in the 1970s when producers realised it could increase yields on marginal sites. He says:
'Boost yields it did! Particularly in vineyards that were more limited in soil or less meticulously farmed. And in an era when growers were less conscious or insufficiently motivated to concern themselves with the connection between quality and yield, the extra 2-3 tons per acre were a godsend and the practice grew exponentially.'
Today he reckons that 95% of California’s vines are irrigated but this comes with a price to pay.
‘Grapevines quickly adapted to the idea that water was closer to the surface and root zones soon began to rise. Root zones closer to the surface meant greater susceptibility to Phylloxera which many blame for the disastrous outbreak in the eighties and nineties.’
‘Greater water availability leads to a dilution of flavour (think hydroponically grown tomatoes) and the rise of green flavours in wine (vigorous growth = green flavours).
Vintners fought back by leaving the grapes on the vine longer and longer with higher alcohols and lower acidities creating a whole new style of wine, quite different from classical archetypes. Summer 'rain' meant weed problems leading to (previously rare) use of herbicides. Wines became diluted in colour – thus mega-purple (a permitted colour additive) and irrigation soon became fertigation as vines found themselves in a nutritive deficit because of depleted soils and more limited root systems.'
For Williams, the biggest problem is even deeper than this negative cycle
'If you believe that the real pleasure of wine lies in its deep connection to the soil, how could you ever be satisfied with a wine borne out of an irrigation pipe and a fertilizer bag?'
Vanya Cullen (Cullen wines, Western Australia) confirms this view:
'Dry farming gives the vine balance in an unmanipulated way. The vine roots go deeper into the soil with dry farming giving more minerality or a sense of the earth than in irrigated vines.'
In Chile, Sebastián de Martino shares a similar philosophy:
'In my view, the essence of dry farming is linked with the concept of 'terroir' – about not interfering with the natural balance of the vineyard which will result in a more honest wine.'
However, he cautions that it is not always feasible in Chile, 'There are few places in Chile that allow dry farming, all of them old vines (over 60 years), on their original rootstock and all of them in the south where rainfall allows – we currently work in four vineyards like this.'
'In terms of the wine, you can see a consistency in what the vineyard delivers in comparison with the irrigated vines. This could also be related to the age of the vines, but our experience is that these vines naturally withstand the different climatic conditions of specific years.' Cristobal Undurraga of Koyle agrees, 'Dry farming in Chile is just found today in the areas where rain is over 600 mm per year. We have our Koyle Don Cande, Muscat and Consult, coming from 70-year-old bush vines that are dry farmed.'
He goes on to explain that he is also trying to reduce irrigation use in other vineyards.
‘The big question is how we could go towards less input of water in our vineyards, so good viticulture is important, getting vines to explore the soil, going deeper and deeper with their roots. With irrigation we have to take care not to teach the vines to be lazy, they have to work for that water, and with the years, the system of roots will be more complex and deep.’
Also in Chile, Rafael Urrejola of TH Wines notes:
'Basically, whenever it is possible to dry farm, and the vines don't get any big stress with that, I will go for it, as the hydric and nutrition balance of the vines is better. Also the wines are usually better balanced, ripe and rounder, with lower pH and better acidity, and with this comes better freshness and ageing potential.'
He goes onto explain that, even though they try to find dry-farmed vineyards to work with, as the dry season lasts from spring to the harvest time, irrigation is an absolute necessity to grow grapevines in many regions. He sums up:
'Usually irrigation is considered as a 'devil' by many people and as a negative tool for terroir expression, quality etc. But, it is not if it is used in the right way and it is the only chance for many regions and producers to grow vines. Correctly managed, it is a positive tool for quality.'