Pruning is the foundation of viticulture. The way vines are pruned speaks volumes about the terroir of a site and adds another dimension to the understanding of wine. The number of buds retained after winter pruning may be influenced by the scientific principles behind balanced pruning, or greed.
Why pruning vines
The most important aspect of pruning is that it regulates the next season’s yield by controlling the number of buds which can burst and produce bunches of grapes. Pruning also allows to space the fruit out for sunlight and airflow. It’s very difficult to achieve proper pruning on each vine, but many of the problems that we deal with in the vineyard and the winery - disease, slow ripening, green character, lack of concentration or otherwise unbalanced wines - can be prevented with good pruning.
Timing of pruning
Pruning is carried out in winter, in cooler regions, once the first frost causes the leaves to fall and exposing the woody canes. But pruning can be done any time from after harvest, ideally once the leaves have fallen until before budbreak in September (as the pruners can damage emerging shoots as they work) which makes it about a four-month window. Traditionally in the old world we would start pruning at Winter solstice, the shortest day of the year, which would be the 21 June in the Southern Hemisphere.
The timing of pruning has major implications. The later the pruning, the later budbreak occurs. We prune some early-budding varieties like Chardonnay, Pinot Noir, Nebbiolo and Zweigelt late to delay budbreak and minimize frost damage. Our vineyard is very well protected from heavy frosts by the nearby Wairau river, but we can have a few very short frosts in spring just before the sun is rising. The weather during spring in Marlborough can be unsettled with prolonged rainfall and cooler conditions and will affect the fruit set.
For larger wineries with many hectares of vineyards to prune, labour issues must be taken into consideration, as not everything can be pruned at the last minute and pruning for them starts normally soon after vintage.
Balanced vines - how much to prune?
How much of the vine is cut off and how much is left, is one of the most critical factors in the entire season of the vineyard. A vigorous vine will tend to be vigorous, and a weak vine will tend to be weak. Looking at a leafless dormant plant with pruning shears in hand and assessing the way it grew the previous year is the first step in deciding how “hard” to prune it.
The number of buds to be left on the vine at winter pruning should be judged relative to the vine’s capacity early in the growing season to support the growth of shoots. In turn, a balanced pruned vine will have sufficient shoot growth to ripen the fruit it carries. We leave more buds on a stronger vine to dilute the growth over more shoots, and we leave fewer buds on a weaker vine to concentrate the growth into fewer shoots.
Pruning method, spur or cane pruning
Along the canes, which were green, soft shoots during the previous growing season, are buds which are arranged on alternate sides of the cane about 8 cm/3 in or so apart. There are different pruning methods, but the two main types of vine pruning are either to spurs, or to canes.
Cane pruning (Guyot) allows for more options: to leave just a short cane, a long cane, two long canes, multiple canes, or any combination thereof. How many canes depend on the required yield. With our low yield philosophy in mind, we prune right back to two short canes. Long canes are not even possible in our close planted vineyard. Conventional vineyards in Marlborough will prune mostly to three long canes as they have less vines per hectare. Four canes is simply greed.
Spur pruning (Cordon) can be flexible too, but not on an annual basis - canes can be altered every year, but once the vine is set up with spurs, they are well fixed.
The goal is to prune the vine in such a way that no fruit is touching, and the vine canopy will be even - no clumps or bare patches. We always remove the last shoot of each cane and the shoots around the head of the vine, typical spots where the shoots can bunch up. Clumps of fruit are plagued with uneven ripening and fungal disease issues. In addition, clumped up leaves adversely affect fruit flavour and acid balance even if the fruit is thinned out and well-spaced. Attention to light distribution is a crucial part of retaining acidity without green characters.
Bare patches in the canopy caused by excessive spacing are problematic too. They expose fruit to direct sun, which robs aroma and colour through overheating of the fruit, or they may even cause sunburn, which contributes bitter and prune-like characters to the wine.
Our experience of pruning 28 different grape varieties over many years have taught us which method to use and how many buds to leave for each vine. On top of all the factors described, the ideal pruning method also depends on grape variety, rootstock, and soil type.
For low yields, spur pruning is ideal as it triggers less vigour and smaller berries. We use this method for the varieties where we look for extremely low yields like all Cabernets, Montepulciano, Lagrein and Sauvignon Blanc. We prune back to about 8 spurs depending on the strength of the vines.
Most of our other varieties are on slow growing rootstocks and if the plants are spur pruned there is too little yield. However, we only leave two short canes (our vineyard is close planted and wouldn’t even leave the space for long canes) with a maximum of 8 to 10 buds for low yields.
To summarize, pruning is not an easy task and requires a lot of knowledge and skills. This is why Hans prunes all the sensitive varieties himself and overseas every pruner very closely.
All for the love of wine, naturally…