Thoughts on vine density

A student asked this question today, and I spent some time on a reply. A good topic for discussion (and final exam questions??? :-)

"Can you explain why low potential soils need closer vine spacing to optimize the yield and quality and soils with higher potential need wider vine spacing?"

"My understanding is that higher soil potential leads to high vigour of the vine and should increase the density of the vine to manage that right? So therefore high potential soil should have closer spacing than the low potential soil."

My answer:

Vine spacing is one of those things that you should really try to get right when you're planning the vineyard. It's one of the reasons why detailed soil surveys are done before vineyards (incorporating variety, trellis, rootstock etc.) are designed. Get the spacing too tight, and the vines will outgrow the volume of space available to them. Get it too sparse, and the vines may not be able to take advantage of the volume allocated to them, leading to unused cropping potential.

To begin this discussion, we should first define what we are talking about. There are two types of spacing: within row (between vine) and between row.

Generally speaking, as you decrease the between row spacing, you also decrease the between vine spacing. However, there is room to move, so to speak, when practicing this.

Firstly, let me tackle the question of soil qualities and appropriate vine density (which, through altering between row and within row spacing, is what we are mostly talking about here).

If a soil is fertile, then there are two trains of thought. One is to give the vine a lot of space to express its high capacity for growth - therefore, low vine density or wide spacings.

The other is to plant with high density to get the vines competing with each other for nutrients and water.

If the soil is not very vigorous, then there are the same trains of thought. Have wide spacings and low vine densities because the vines will then have little competition (assuming weeds are kept under control) and therefore access to the most water and nutrients that they can.

This sort of spacing is used in dryland farmed areas, where irrigation not feasible. The vines are trained as bushes, with perhaps only a stake for support. Because of this, yields per hectare are low, but then at least you can get something off the land - it's just not an intensive producing area (the most planted vine data I showed in my cultivars lecture demonstrated this - Arién has the most area planted to it, but the vine density, and therefore yields, would be very low compared to some other varieties).

Or, if you can add water to the equation, you can plant them closer together so that you can get a continuous canopy and therefore more productivity per unit area of land.

So determining the appropriate vine density depends not just on the soil, but also how it's going to be managed. The question referred to this as optimising the yield, which is the key.

So, with that out of the way, let's talk about vine spacing in terms of what is practiced in the Old World versus the New World (using gross generalisations here, so please bear with me...)

In the Old World, some of the best wines come out of vineyards that are planted at around 1mx1m, or 10,000 vines per hectare. This compares to the usual 3mx2m spacings (1667 vines per hectare) in most of the early New World plantings, including a lot of Marlborough Sauvignon blanc (I assume everyone is familiar with how those spacings came about??).

The reasoning used by some is that because great wines come off of vineyards with close spacing that it must be the close spacing that contributes to that wine quality. Therefore, if we replicate that spacing in another place, we will get better wines.

However, as reasoned above, it's actually a balance of the soil and overall management that really results in achieving vine balance (open canopies and an appropriate ratio between fruiting and vegetative growth), where it's easiest to get the most quality out of your fruit. What often happens when close spacings are transplanted to another area is that the vines end up being vigorous and turn into a mess of shoots and canes that would send Richard Smart into conniptions!

Why does this happen? Well, in many New World areas, the soils are a lot more fertile and deeper than soils in the Old World, where they have been farmed for centuries (and are often on hillsides). It's true that close vine planting will result in root competition to the sides, but what if the soil is deep? The roots can grow down and away from competing roots and fine plentiful nutrients and water. Therefore, they grow like triffids, and viticulturists may resort to pulling out rows and vines to get it into balance. We just can't control growth of roots down into the soil - unless rainfall is low, and irrigation is used...

And that last point is really the crux to the discussion: viticultural management can alter what might not be the best vine spacing into a system that still produces optimum fruit. If the spacing is too tight and vines are growing out of the volume allocated to them, we can reduce irrigation, or plant a more competitive cover crop, make the weed-free strip under the vines narrower, change the training system, or, if it's dire, rip out some of the vines...

In practice, this happens all the time - though we try to get as much information as possible pre-planting, we are still just making a best-guess as to the vineyard setup - the best way to know how vines will perform in an area is to plant some and see how they go over a 10-15 year period. This is why vineyard redevelopment, as we have see in many areas due to phylloxera, for example, is really an opportunity.