While numerous training and pruning systems exist, three basic
canopy structures serve as a starting point in deciding on
the best trellis system for your vines.
By Mark Greenspan
From Wine Business Monthly, 10/14/2006
Vineyards are not natural systems. If a grapevine had its way,
it would: (a) not be grafted onto some strange rootstock of a
different species mix, (b) not be grown on some shattered rock
hillside nor in the middle of the desert, (c) have its fruit
eaten by birds or deer rather than being shipped across the county
or state to some processing plant, and (d) rather grow up the
side of a tree than up a steel stake and thin wire. Trellis systems
were developed to channel the grapevine's natural tendency to
grow upon other structures into a form that serves our purposes
for improving both vineyard productivity and wine quality.
Over the years, there have been countless variations on trellis
system designs. Coupled with numerous training and pruning styles
(most generally divided into either cane or spur-pruning, or
hybrids of both), the number of permutations of trellis, training
and pruning systems is mind-boggling. Many of the trellis systems
developed in the last few decades have come from universities
and growers in cool-climate grape growing regions (e.g., New
Zealand, New York, Oregon and some regions of France).
The goal of much trellis development has been to maximize the
leaf area to capture more sun energy and increase productivity
in regions that experience short seasons (due to late spring
and early fall frosts). But those systems do not always perform
well in warmer growing regions where they may be completely inappropriate.
There is no need to cover all of the trellis types and training
systems out there. I have found that the topic is well covered
in Freeman et al., 19881. I will instead discuss the systems
in general terms. I like to think of three basic categories with
regard to their canopy structure: head-trained, non-divided and
divided vine canopies.
Head-trained
In a head-trained vineyard, vines are not trained onto a trellis
but are left to be on their own (not connected to other vines
by a trellis system). In actuality, a cane-pruned vine that is
on a trellis is also head-trained, but the common colloquialism
for non-trellised vines is "head-trained." Australians
refer to them as "bush vines," which is probably a
more meaningful descriptor.
Head-trained vines are trained to a vertical trunk, often without
a strong support structure and are usually pruned to spurs that
emanate from all directions out of the center. Most often, the
shoots are allowed to grow without any manipulation, where they
droop over and trail on or near the ground. Many older vineyards
were planted in this fashion, which allows for planting on a
square grid, and cultivation or other cultural practices may
be performed in two directions (i.e., cross-wise). Such vineyards
are frequently non-irrigated.
Some people swear that this system is the only way to grow Zinfandel
and, because of that feeling, a few new Zinfandel vineyards are
still being planted in this manner. It is, however, likely that
Zinfandel grown on a different trellis system can match the quality
of a head-trained vineyard.
The major disadvantage of this system is that it is not easily
managed using machinery, which makes it uneconomical for most
operations. Machines, such as sprayers, leafers and cane-cutters,
work in a linear fashion, and the head-trained vine is not trained
in a line. Furthermore, the fruit may get buried under layers
of foliage, especially on vigorous sites. Under those conditions,
some fruit will not receive ample sunlight, possibly causing
fruit to ripen unevenly. Additionally, it may be difficult for
protective sprays to penetrate into the cluster zone when under
the thick blanket of foliage. That is why this system is most
effective on low-vigor, non-irrigated hillsides where shoot growth
does not become rampant.
One adaptation of the head-trained, spur-pruned vine is the
Gobelet system, in which the shoots are tied up to a stake (which
also supports the vine), forming a goblet shape. This avoids
the cluster shading indicated above but leaves the fruit potentially
overexposed to direct sunlight.
In another variant, the vines are cane-pruned, and the canes
are tied up to a central stake. The vertical canes, however,
are more likely to develop conditions for variable fruit maturation
within the interior of the canopy.
Aside from its traditional association with fine Zinfandel vineyards,
the primary advantage to the head-trained trellis system is that
the vineyards are stunningly beautiful during the winter dormant
season.
Non-Divided Single Fruit Zone
The "single fruit zone" category undoubtedly captures
the majority of the systems in use, at least in California. These
trellises have one single fruiting zone that forms, in the abstract,
a straight line running down the vine row.
At its most basic, a single fruiting wire supports a horizontal
cordon (or canes), and the shoots are left to grow in many different
directions. This has been referred to as the "California
Sprawl," but that notoriety has been largely negative. That
is because many sprawl vineyards have historically been over-irrigated
and over-fertilized to the point where foliage was everywhere
and not a cluster was to be seen without some serious digging.
Notwithstanding the jungle-style sprawl vineyard, the single-wire
trellis, if managed properly, can be the best solution for many
operations. Warm, interior valleys and some coastal valleys that
experience several hot spells per year might be better off with
a single-wire system than with a more modern shoot-positioned
system. The "fuzzier" canopy of the single-wire trellis
will allow less direct sunlight into the fruit zone, which will
protect the fruit from overheating. It is important to manage
the water and nutrition of these vines so that they do not venture
into the classic California Sprawl territory.
The T-trellis was and is still used to lift the foliage up and
away from the fruit zone. Two additional catch wires at the ends
of a crossarm (hence the "T") retain the shoots as
they grow upward. For this system, the shoots will need to be
tucked between the catch wires, which usually requires more than
one pass through the vineyard.
Shoot-positioned trellis systems are the current state of the
art and are found in most high-end coastal vineyards. Shoots
are positioned vertically upwards as they grow, using movable
wires to lift the shoots. The vertically-shoot positioned (VSP)
system allows for rows to be positioned more closely together,
thus increasing productivity per acre. But the primary reason
for such a system is to provide an optimal sunlight environment
in the cluster zone, known as a "dappled" light. Fruit
is generally located in a single linear band, which promotes
uniformity of quality and ripening. That is why winemakers generally
favor this system over most others.
Generally speaking, little or no leaf removal is necessary in
VSP systems although some leafing is often practiced, especially
in tight-clustered varieties2. The VSP trellis may not be the
best solution in interior valleys as fruit may be under-protected
from sunlight and may be damaged during heat events.
Another downside to the VSP is that it does not perform well
in high-vigor situations. Some of the vigor may be toned down
through wider spacing of the vines, which allows for a greater
amount of wood (dormant buds) to be retained per vine. However,
on high-vigor sites, foliage may become too dense, and leaves
become scrunched up within the tight space between the wires,
creating a leaf canopy that does not collect sunlight efficiently.
Furthermore, vigorous vineyards will require repeated passes
with a cane-cutter in order to maintain the hedgerow shape that
is sought after. Multiple cane-cuttings per season (an unacceptable
situation in my mind) is a sign that the vineyard was poorly
designed from the beginning.
There are other variations on the undivided fruit zone theme,
including splitting the foliage into two curtains (Wye trellis)
that alleviates some of the foliage bunching that occurs in the
VSP. More commonly, positioning wires may be spaced out wider
so that the foliage is not as compressed.
Divided Fruit Zone Canopies
Divided fruit zone (or divided canopy) trellis systems all have
two fruit zones. They can be horizontally or vertically divided,
though the horizontally divided trellis systems are by far the
most common. While some winemakers may be convinced that the
divided trellis is simply a way for growers to satisfy their
greed, most often it is a way to deal with a vigorous site that
cannot be trained to a single fruit zone without excessive vegetative
growth. Most of these systems will have two parallel fruit zones,
spaced about two to three feet apart. Vines are usually trained
to cordons in a quadrilateral configuration (an "H" shape
when looking from above) or in an "S" or "U" shape.
Vines may also be trained to a head and cane-pruned to four canes.
The shoots are usually positioned either straight up or are
tilted over a bit and are positioned with "rake wires" that
open up the center of the canopy to allow sunlight to penetrate.
There are many variations on this theme, but the most common
is probably the Open Lyre trellis system. In the Geneva Double
Curtain (GDC) system, developed in New York, the cordons are
trained high up and shoots are encouraged to droop downward.
The GDC system is not appropriate for warm growing regions as
the fruit tends to be overexposed to sunlight.
Horizontally divided systems have two fruit zones that overlay
one another in a vertically oriented plane. They are all very
similar to the VSP in that they are usually shoot-positioned.
However, the upper tier in such systems is similarly trained
to a VSP while the lower tier is inverted and the shoots are
positioned downward so that the lower tier does not shade out
the upper.
There are several variations on the horizontally divided theme.
The terminologies seem to keep getting mixed up and I am always
frustrated in trying to figure out exactly which name goes with
each training system. Nonetheless, Scott
Henry, an Oregon winegrower
and winemaker, developed the original system of this kind. He
laid out four canes per vine and trained each pair to a different
fruiting wire. The lower canes were rolled over and positioned
downward, thus leaving two fruit zones open. There have been
variations, including the use of cordon-trained vines and alternating
up- and down-trained vines within the row3.
In my experience, vertically divided trellis systems are appropriate
only for cool-climate viticultural regions. In warm and hot climates
the fruit zones tend to be far too exposed to direct sunlight
and the fruit is often damaged by excessive heat, especially
in the lower tier, which is closer to the warm soil.
The Best Trellis System
I share the winemakers' preference for single-canopied trellis
systems. As I mentioned several months ago in an earlier article4,
two fruit zones, whether divided horizontally or vertically,
will develop under different light and/or temperature conditions
and will not have the same qualities at the end of the season.
For the same reason, they will not ripen simultaneously; and
if care is not taken to harvest them individually, wine quality
is unlikely to attain the same levels of quality as a single-canopy
system.
With that said, I understand that there are numerous vineyard
sites where a single fruit zone canopy may simply become a green
monster; therefore creating a divided canopy will be completely
appropriate for those locations.
And so, what is the best trellis system for winegrapes? One
might as well ask, what is the best variety of winegrapes? wbm
1 Freeman, B.M., E. Tassie and M.D. Rebechi. "Training
and Trellising," Viticulture. Volume 2 Practices. B.G. Coombe
and P.R. Dry, editors. Pp. 42-84.
2 Greenspan, M.D. "Pitfalls of Overexposed Fruit." Wine
Business Monthly. September 2006.
3 Smart, R. and M. Robinson. 1991. Sunlight into Wine. Winetitles.
4 Greenspan, M.D. "Taming Fruit Variability." Wine
Business Monthly. December 2005.
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