The grapevine is a liana with important vegetation, and belongs to the Ampelidee family, genus Vitis. Left in the wild, it spreads rapidly and the buds, in some varieties, can reach 100m.
It's a climber by nature that continues climbing until it finds an anchor. If not pruned, it quickly turns into an irregular bush with disorderly vegetation, very irregular production and would only produce small fruits of poor quality.
Pruning, on the contrary, keeps it in a suitable form that facilitates work on the ground, ensuring the plant a certain longevity.
The object of pruning is also to regularise fruiting, ensure the fruits’ normal development and high quality and provide the plant with a shape and size that’s proportionate to its force and the specific climate in which it’s located.
Man first practiced the propagation of the grapevine in a simple vegetative way, then later started selecting buds, improving the first vines through seeds and cross-breeding and then applying grafts, all acts that enhance fertility.
This latter technique greatly development after the phylloxera invasion. Important research is being made in the field of genetic improvement, research that aims to produce once again in all the qualities of our European varieties a greater resistance to certain diseases.
To better understand the pruning of grapevines, it’s essential to know some well established basic principles:
- Unlike fruit trees, the grapevine doesn’t heal its wounds!!
We know that fruit trees cover their wounds through the formation of scar tissues. The vine, on the contrary, doesn’t have this ability. So when pruning, you must remember that each scissor cut creates a wound that will never close. Often the wound enlarges; causing tissue death (decay of the woody tissues), which, depending on the severity, may variously obstruct the lymph circulation.
Example: when two necroses positioned on opposite sides meet, it results in a total shutdown of lymph circulation inevitably causing the death of the affected area or even of the trunk, if it’s been wounded (Figure 1).
The herbaceous shoots that are removed during the green pruning do not incur the same injuries and do not form necrosis because they’re not woody yet.
All lesions, pruning wounds and subsequent necrosis, strangulation and twisting suffered by the trunk or shoots limit their growth. To perform a good pruning, you must try to not inflict some of the damages described.
- Vineyard vegetation is directly related to the strength of the rising sap.
The more vertical the plant is, the stronger its vegetative force. A vertical branch will give rise to more vigorous shoots than one positioned differently, and development will be greater at the ends. Instead, if a branch is kept horizontal, its vegetative activity is more limited and will be minimal if you curve it into a downward position.
It is therefore necessary to refer to some rules on trunk formation for most grape varieties: give the trunk a head with a direct and rapid lymph arrival, forming side (arms or horns) that will serve as lymph moderators and regulate vegetation and production. The stem grows upward and it’s ideal, especially when pruning for the renewal of fruiting, to predict and prepare renewals under the wounds in a dynamic way: some years you go up and others down again in order to contain the stem within acceptable heights.
- The most fertile buds are found on one-year-old wood grafted onto that of two years.
This explains why the shoots that come from old wood are generally not fertile, at least in the first year.
They can bear fruit in some varieties, but in general, they are considered useless, which is why you tend to eliminate them.
Whereas, the canes derived from them in the following year will be fertile if stored.
Pruning the cane that comes from two-year-old wood secures the highest fertility but lengthens the fruiting and therefore the lymph path. Between these two systems, you should choose a middle road, which dictates normal pruning. Or what winemakers call prune the young or prune the old.
- The buds are much more fertile the more distal they are from the base of the cane, and this occurs generally up to two-thirds of the cane, after that, the fertility potential is reduced.
Long pruning bears more fruit, but quickly exhausts the plant.
Short pruning can be a wood pruning in very vigorous grape varieties, but, as a general rule, reduces production for the benefit of longevity. It represents normal pruning in our hilly vineyards.
The vegetation of a trunk is proportional to its age, which is recognised by the length and diameter of the grapevine shoots and by the development of the plant.
Pruning must be adapted to the vigour that occurs.
Fertility is generally inversely proportional to the plant’s vigour. A weak plant often leads to a lot of grapes that struggle to mature, while a too vigorous plant produces almost nothing. Plants that are vigorous but also grow their canes in a moderate way have the best performance.
Pruning, as I’ve already mentioned, allows you to adjust the vigour and achieve a relatively smooth production.
The vigour of the grapevine shoots is proportionate to their numbers. The more branches, bud points and bud load, the weaker the development.
Through pruning and disbudding, you must contain the bud load to obtain a plant in balance with its vigour. If you want to reinforce a weak plant, decreases the bud load and create short spurs.
If, on the contrary, you want to contain vegetation on a vigorous trunk, you need to leave a greater bud load and prune later.
Pruning should be carried out on mature canes. The frozen, white and dry wood is to be removed. Ideally you choose the one-year-wood grafted onto that of two years as the renewal. You try, through pruning and disbudding, not to unnecessarily lengthen the plant, to avoid closed corners and always leave one side wherever you prefer on the lower part of the trunk without scarring, so that lymph circulation can take place normally.
You must also try not to make opposing cuts. Dry areas oppose the sap’s path and the plant tends to dry out.
Avoid major injuries by cutting perpendicular to the grapevine shoot and not obliquely.
I recommend using a very sharp scissors, so that the cut is clean, burr-free and the chosen cane is not squashed. Also, as large scars are very destructive, you should avoid pruning too flush to the renewal section or in the old bud points of the previous year.
To prune the buds in fruit, cut about 2cm above the bud itself. In young vines with weak vegetation and where the internodes are close, you can cut along the top eye.
If the cut is made too close to the bud, it’s possible that the developing bud will no longer be resistant to wind and break more easily.
The wood of the renewal cane can dry and crack under the sun, and this can prevent the germination of buds located too close to the cut.
The grapevine must be well to resist the wounds caused by the scissors during the different pruning. But if the empirical pruning exercised by certain winegrowers doesn’t immediately kill the plant, it considerably shortens its duration to the detriment of the quantity and quality of production.
It is therefore not enough to insist on the need to undertake the maximum care through reasoned pruning in as much as a properly pruned grapevine will produce and last much longer over time than a mechanically or indiscriminately pruned vine.