Buds and canes and shoots and spurs

Pruning methods is a topic I really struggled with for a while. What is the difference between spur and cane pruning ?  And why might one method be preferred over another.

The starting point is to understand how a vine comes to bear fruit. Central to this is the “bud”.  Buds are created on shoots around the flowering time. So as the shoot is busy making a grape bunch or two for the vintage year, by the time of that year’s flowering the shoot has already established on its length new buds from which shoots would grow the following year. During the vintage year each bud will develop a shoot and each shoot will typically produce one or two bunches of grapes.  (It is possible a bud may develop a primary and a secondary shoot - but for our purposes let us think in terms of just one shoot per bud). During the vintage year that fruit bearing shoot lignifies and itself becomes a cane, which will have buds along its length ready for the following years development into new shoots.  And so the process would continue uninterupted absent pruning.  The vine would each year develop more and more buds and thus yield more and more fruit.

The purpose of pruning of course primarily is to limit the number of buds since this limits the number of subsequent fruit bearing shoots growing from the buds, which in turn limits the number of grape bunches.

There are basically two ways do this. 

Cordon or Spur Pruned

The first is a system where the trunk of the vine has been trained to grow laterally /horizontally - on either one side or both sides of the trunk. This cordon has short “arms” along its length from which one or two shoots will grow. At pruning in the winter you cut down the lignified shoot (now called a cane - and there may be two) that emerged from each arm so as to leave just a single short part of one cane with two buds.  These buds grow new shoots in the vintage year.  Essentially one limits the number of buds by leaving each year after pruning just two buds on each of the cut back canes.  This small length of cane now containing two buds is called a “spur”- and several spurs run along the length of the cordon. After many years of accumulation these old spurs start to look like a small upward extensions of wood of the vine along the cordon - like ‘arms”.  This is “cordon” or “spur trained” method.  

Guyot or Cane Pruning

The Guyot method is different in that the number of buds is limited by allowing the full length of just one lignified shoot from the prior year (a cane) to remain on the vine during the vintage year. This lignified shoot will be trimmed the prior winter if it is too long so that along its length there are perhaps only eight or ten buds.  It is positioned horizontally along a wire. These buds produce shoots in the vintage year which are trained vertically on higher rows of wires. At the end of the vintage year this entire cane - which bore the fruit of the vintage - is wholly cut away.  To generate / have available a cane with buds along its length for the following year, each year at the time of pruning another cane is left with just two buds (for security - only one is actually needed). This is a single spur. This bud forms a single shoot in the vintage year, which in turn becomes the fruit bearing cane the following year. ( It would itself grow a single or pair of grape bunches in the vintage year - but its primary purpose is to be/provide the cane for the following year). If two shoots grow out of the spur then the pruner would simply chose the better of the two canes to set along the wire. Normally the side of the vine on which the two budded spur is left alternates so that the vine trunk over the course of many years continues to grow straight. 

The reason behind the nomenclature of each type does actually make sense. Cordon is spur pruned because one is cutting to leave many spurs each with two buds along the length of the cordon. You are pruning to create spurs. With Guyot pruning, one might think of it as cutting away all the canes after each harvest, leaving just one spur with two buds on the other side of the vine and one long cane which is horizontally tied to the wire. So Guyot pruning is not leaving spurs by partially cutting back many canes. Rather it cuts away the entirety of the canes and thus is called “cane “ pruning” .

Since Cordon training extends the trunk of the vine into its horizontal sections there is such more wood on a cordon trained vine than a Guyot trained vine, whose wood is essentially limited only to the truck itself. The smaller amount of lignified wood of the Guyot pruning method makes the vine less vulnerable to frost and as a consequence is the more popular of the two methods in cooler climates.  

Cordon pruning is capable of being pruned by machine or with a hedge clipper. Guyot pruning takes skill.  

There are many variants of Cordon pruning in particular. 

Bush trained / Head Trained. 

The third method is bush trained or ‘head trained”.  Essentially this is spur pruned - like Cordon - except there is no lateral extension of the trunk.  Spurs from previous years form in all directions directly from the top of the trunk and thicken up over the years to become arms.  

For great diagrams of these variants I suggest you go to Wine Folly’s website.  

Hedging and Braiding

This is a hot topic on which I feel completely unqualified to make a post.  But - among high profile Domaines in Burgundy and many prestigious properties elsewhere - in the viticulture space it is very much the topic being discussed.  So it merits a brief post to introduce the subject, accompanied with a strong recommendation to find other more authoritative sources to guide you through the topic in more detail..   

For this particular summary I am indebted in large part to the Wineanorak.com site 

The question relates to canopy management. At issue is what to do with a vine’s long lead shoots and accompanying “excess” foliage that may continue to develop from the top of the vine in the period leading up to and after veraison. The traditional approach is to remove this excess vegetation by cutting it away by hedging clippers installed on a tractor - hedging or “rognage” - with the purpose of getting the vine to focus not on producing additional leaves but on producing and maturing fruit. In the normal course versaison is the time the vine, if in perfect balance, would make this transition of its focus from vegetative growth to fruit development naturally.  But this is seldom the case. Vegetation continues to grow if nutrients are still available. 

The latest idea, however, is that this hedging is harmful to the vine and a process has been developed - initially as I understand it by Domaine Leroy from about 1999 - not to cut the vine at all but to “braid” the excess foliage by folding it in on itself and rolling it together - a term the French call “tressage”.  Alternatively the tips can be strung along the top wire to meet the neighboring vine. This process is terribly expensive. According to Charles Lachaux of Domaine Arnoux-Lachaux in Vosne Romanee, tressage takes perhaps twice the time and four times the number of workers as conventional hedging. Pruning the subsequent winter is also more challenging. 

The reason for braiding the vine is primarily that if you cut the top part of the vine away its natural response is only to produce more lateral shoots to compensate. And lateral shoots are a particular problem because they shade the fruiting zone.  Any home gardener will buy into this rationale.   

But given this widespread adoption globally - from Piedmont to Alsace to the Finger Lakes - as you might expect the list of other benefits asserted by its proponents is long.

One is that the berry bunch forms more loosely if the vine is not hedged because the little rachis stalks to which the berry is attached grow longer, which improves airflow through the bunch and thus reduces the likelihood of rot.  

Other claimed benefits - from growers in Piedmont - are that tressage keeps the pH low in the resulting must and reduces sugar in the grape - though work by David Croix in Burgundy on his Beaune Bressandes vineyard suggest neither acid not sugar are impacted.  He nevertheless endorses the approach because, without necessarily being able to attribute a reason, his empirical tests do result in a favorable difference in the wine that was made from grapes subject to tressage relative to the wine made from vines that were hedged. 

Given the high labor cost of performing the braiding, some are considering simply hedging in the conventional way but doing this as late as possible. 

There are many unknowns here.  In particular what is the role played by the extended foliage and the very tip of the vine ?  From one’s opinion on that flows a view on what you lose if you cut away that tip, which in turn informs whether one is willing to incur the considerable cost of keeping it. 

The picture shows Domaine Leroy vines Romanee St Vivant, taken in December 2016, which illustrates the braiding technique

The most important decision

When to pick your grapes was always an important decision. In times past one picked when the grapes had sugar levels sufficient to allow the winemaker to make a wine with the desired amount of alcohol, even allowing for some extra sugar to come from chaptalisation.  Historically, when it was often quite hard to get grapes to be fully ripe, achieving this level of sugar ripeness was the primary goal.  If the highest level of ripeness you were likely to get in the grapes perhaps was only potentially 12 degrees of alcohol, you did not have to worry about whether the acidity would be adequate.  And not much was known in the early days about phenolic ripeness. So sugar ripeness alone determined the picking date, making the decision when to pick relatively straightforward.

But today this decision is more challenging because of two factors  -

1. Risk of “overripe” grapes is greater because of the warmer climate

In today’s warmer climate grapes can ripen easily and can quickly become overripe with a commensurate undesirable reduction in acidity. Grape varieties vary in the relationship between the rise in sugar levels and the reduction in acid. Some grape varieties lose acidity more quickly than others as sugars rise. But all grape types have an easier time today getting fully ripe - and some grape types can become too ripe in a matter of days. 

Also, as the climate has warmed, if picking dates have as a result moved to late August or early September when previously they were towards the end of September or early October, the reality is that each day the grape remains on the vine starts to matter more. This is simply  because each day in late August is a warmer day than each day in late September. Harvesting grapes in October is more forgiving than if you have to harvest in late August. A day or two either side may not matter. But the picking “window” is shorter if you must harvest in August. Managing picking teams is more difficult if the window is smaller. Picking schedules can become very tight. The days of leisurely picking in October on your own schedule are apparently over.

2. The need for phenolic ripeness 

Today we better understand and acknowledge the importance of a second type of ripeness - the ripeness of the skins and the seeds - which is quite different from sugar ripeness. This Is called phenolic ripeness, which is needed to produce optimal ‘flavor” and structural ripeness in the wine. The path to phenolic ripeness does not necessarily run coincidentally with the arrival in the grapes of ideal sugar ripeness.  Typically - and this is a generalization in the old world  - phenolic ripeness comes later than sugar ripeness. So one may have grapes on the vine with the perfect sugar/acid balance but that have not yet reached full phenolic ripeness.   Without adequate phenolic ripeness a wine will have some green flavor notes and underripe tannins.  Within certain boundaries, it seems phenolic ripeness has more to do with luminance ( ie light) than heat, whereas sugar ripeness is more determined by levels of warmth.  So they may not arrive at the same time. Whether they do depends on the particular climate of the year. If they do not arrive more or less at the same time, a winemaker will have to choose which type of ripeness to prioritize. Waiting too long for phenolic ripeness may result in grapes with high potential alcohol and low acid, giving flabby wines. Picking too soon may result in perfect balance between fruit and acid but suboptimal flavor elements and unripe tannins because phenolic ripeness was not yet achieved. In extreme seasons the choices can be quite stark. In Barolo’s 2017 vintage, for example, the unusually long period of dryness shut down the grapes’ vegetative cycle. The result was that the picking date was largely determined by the desire not to lose too much acid, thereby having to accept that the skins and pips would not be fully ripe.

So there are at least three three dimensions that factor into choosing a picking date - sugar ripeness and the commensurate related acid level, and phenolic ripeness.  Most growers making a red wine prioritize phenolic ripeness over sugar ripeness - not least because they have some ability to control delaying sugar ripeness. There are many vineyard techniques to try and slow down the rise in sugar in the grapes - managing the leaf canopy for example to slow photosynthethis or allowing yields to increase a little by not green harvesting. Slow down the sugar ripening process and you better align the optimal sugar ripeness with phenolic ripeness.

There is a point of view that, in a year of extreme imbalance between sugar and phenolic ripeness - beyond what can be compensated for by the techniques used to slow down sugar ripening - if you pick early and so risk some less than optimal phenolic ripeness, the resulting wine may over time in bottle recover somewhat from that. Time has the effect of moderating the imperfections in the tannins. Whereas if your preference in such a case is to pick late to ensure full phenolic ripeness, the resulting high level of sugar ripeness and reduced acid will always mark the wine. Time has no ameliorating impact on a wine that starts out “flabby”.

Greater awareness of these interlocking variables make the choice of picking date today even more challenging than previously.  There is more understanding about the likely consequences of choosing a particular day over the next. More informed decisions of course give the winemaker more control. But the decision is still a stressful call - an irreversible decision which puts in play the work of a whole year in the vineyard. If you ask a vigneron what “mistakes” he has made or what he would have done differently in relation to a particular vintage where he feels the wine might have been better, the most common answer you hear is that he picked too early or too late. 

If you have any doubt about the importance of picking date, try a few 2006 red burgundies. 

Rootstocks

This is a subject that deserves more attention than I can possibly give it. Rootstocks was certainly a topic about which I had no understanding whatsoever until I tackled the WSET Diploma program, at which point I began to be rather too fascinated by the subject. I found the particular qualities and tolerances of each basic rootstock type - and that their crosses did not always bring only the best of both contributors - compulsively interesting. This is real agriculture. 

One hears often of vines being pulled up because they gave in some way less than optimal fruit.  But they can also be pulled up because the rootstocks were not suitable - most particularly if too prone to chlorosis (the lime in limestone turning the leaves yellow and inhibiting the uptake of nutrients) or phylloxera.  

Vinifera is the original native European rootstock - not therefore naturally resistant to phylloxera which was not present in Europe until imported from the US in the 1860s.  The US vines by contrast are all to some degree resistant to phylloxera since the insect is native to the US. So you graft a Vinifera scion (the part of the vine that you see above the ground) on one of the three American rootstocks or more likely some cross of these so as to generate the optimal results for the soil type and climate of the vineyard.  If you cross a Vinifera rootstock with a US rootstock you run the risk of the result not being sufficiently resistant to pylloxera since one of the parents is the non resistant European rootstock.  This was the problem with AXR1 in Napa. But that cross is still used in Champagne where the sandier soils are less hospitable to the insect, since AXR1 has the desirable quality of being particularly resistant to the high lime content of those soils. And so it goes….

Oversimplifying considerably the basic US rootstocks are - 

    Riparia           Gives low vigor but has low resistance to drought - so good in damp soil

    Rupestris       Gives high vigor and has good resistance to drought - so good in dry soil

    Berlandieri     This has strong resistance to lime - so good in soils with a lot of calcium

These can also be crossed. For example 

    AXR1                      Cross of Vinifera and Rupestris - still to some degree susceptible to phylloxera

    3309C, 101-14        Crosses of Riparia and Rupestris - does well in high acid soil

    161 / 49C /SO4      Crosses of Riparia and Berlandieri - moderate vigor and resistant to lime

    99 (Richter)           Cross of Rupestris and Berlandieri - Good resistance to chlorosis / deep rooting                   

And there are dozens of other combinations. 

The choice of rootstock when planting a vineyard is of course a huge decision. Errors are costly in the extreme. One has only to look at California’s experience with XR1 to witness what a catastrophe can result from a poor choice. As well as picking a rootstock with sufficient resistance to disease and that is suitable to the particular soil type in which it will grow, decisions have to be made about plant density and predictions about the future climate. And although the science in this space is hugely improved, there are still many unknowns. For example, it is not yet understood why certain rootstocks in Burgundy are dying earlier than expected.