Nature vs Nurture: A Grapevine Story

Mark Krasnow and Karen Peterson

I was asked to talk at the recent NZ Organic and Biodynamic conference about the grapevine and how we farm it optimally for winemaking. As part of this talk I took the audience back, all the way back to the origins of grapevines. Grapes are lianas which utilize the structural support of other plants so as to elongate their shots faster than the competition to get to the sun. This is a fantastic strategy, since vines can focus their energy into growing shoots and roots and developing fruit without having to invest in as much structural support as other perennial plants, like trees. This means much more rapid growth for vines, which is important when the structure you are trying to outgrow is also growing.

Grapes in the wild, by necessity, have to grow in competition with other plants and have developed many strategies to do so, including a climbing habit and tendrils to allow for easy climbing. The normal for grapes in the wild is having to fight for nutrition and water, and compared with other crops, their needs for both are relatively minor. However, when given ample resources, vines can grow extremely long shoots quickly, and unlike many trees with determinate growth, can grow shoots all season long. This gives them the advantage when racing to the sun against other plants.

Another advantage grapes have developed is the extreme degree to which they make mycorrhizal associations. Mycorrhizae are fungi that live in the soil, which can make symbiotic relationships with vine roots, providing the vine with nutrition and water in return for sugars. These associations dramatically increase the amount of soil the vines roots are able to “explore,” and thus provide the benefit of additional soil resources. This allows grapes to thrive, even when growing in extreme competition, often with much larger plants. Given they are exceptionally good at making mycorrhizal associations, and in the right conditions, most grapevine roots will have many mycorrhizal arbuscles (the exchange site between the fungus and to the vine).

A wild grape growing up a walnut tree. Photo credit: Jaime Goode.

Grape seeds, for the most part, are dispersed by birds, which means the vines want to put fruit out in the sun where it will be easily seen and consumed. In the wild, this results in fruiting structures mainly made high up in the branches of the tree the grape is climbing. Fantastic strategy for the grape, but not by any means ideal for humans looking to harvest the fruit. Humans, being very smart, “domesticated” the vine and began to grow them on trellis and to prune them so that the fruit would develop in more convenient places for us. However, the domestication process did not mean vines became completely devoid of their natural tendencies.

Raising Resilient Vines

As part of this domestication, we took the vines out of the forest and began to propagate them clonally in vineyards. This is the origin of modern viticulture. We brought the vines out of the wild, but the wild nature of the grape remains. Jeremy Hyland, a very good viticulturist, described the modern vineyard as “lonely vines with no friends to talk to except clones of themselves,” which I thought summed up the situation pretty well.  Understanding the wild nature of the grape is the key as we look to optimise viticulture and winemaking. However, I often see growers adding fuel to the "fire" of the vine’s nature, then fighting the fires they've created.

As Viticulturists, we are part of a wine and table grape business, which to remain viable has to make money. For many this means trying to “optimise” the yield of their vines, but many of the strategies I observe are rudimentary and can end up undermining the vines evolutionary traits designed to help the vines thrive.  Removing all the competition with herbicides or tillage and then watering and fertilising the vines to provide the nutrition that would have been scavenged in the wild by roots with their mycorrhizal partners is expensive. This strategy can, undoubtedly, lead to high yield, but I feel the quality of the wine suffers with such “scorched earth” practices. Growing such a genetic monoculture, modern vineyards are more susceptible to insects like leafhoppers and mealy bugs, which have no alternative host plants in such a system, and have no habitat for their natural predators. Also, the long term sustainability of applying lots of water and fertiliser is questionable. Fresh water resources are under more and more pressure due to climate change, pollution, and the expansion of urban areas. Fertiliser costs are continually rising, and for those that are climate conscious, the production of synthetic, and even some organic, fertilisers has a relatively large carbon footprint.

Harmful Beauty Standards

We have become accustomed to the straight lines of mechanically or chemically managed vineyard floors and the neat hedges of vines. To many, this is the visual of a well-managed vineyard. I have a different aesthetic. The modern vineyard is about as far as one can get from the grape’s natural habitat—it’s a large monoculture of genetically identical vines, with (perhaps) some grass or “cover crop” in the midrow. I prefer a more natural look, embracing the “wild,” where viticulturists foster species diversity as part of their management strategy within the confines of the monocultural leaning vineyard systems. This “messy” look is closer to how grapes evolved, and helps viticulturists foster resilient vines, which in turn have a greater potential to produce substantially higher quality fruit for winemaking.

A very clean undervine from cultivation before budburst. Some organic growers try to maintain this aesthetic all season, necessitating many passes.

Organic practitioners have to, or to a certain extent are forced to (willingly or not) , embrace the “wild” more than their conventional counterparts. They are also more reliant on cultural practices and “natural” nutrient management strategies such as cover cropping. Almost all of the “iconic” and highest rated wines from New Zealand, especially of Pinot noir, are from Organically or Biodynamically managed vineyards, and this is not an accident. Fruit from these vines tends to have smaller berries, more colour, and more flavour density. Tonnage can be bumped up substantially in the modern conventionally managed vineyard, but the wines from such farming can often lack personality and nuance. It’s a quantity versus quality question, and the right balance for each vineyard and winery will differ.

However, even in the organic viticulture space, I see some less-than-ideal practice. Many organic growers in New Zealand will till undervine 4-6 times a year to maintain a bare strip under the vines to “reduce competition”. In drier areas, organic practice is even more extreme (and in my opinion poor), with everything except grapevines tilled out of the vineyard. No other plants means many fewer mycorrhizal associations, and those that do form are disrupted when the shallow roots that have them are tilled up. This makes the vines reliant on what they can get from their own roots, which often isn’t enough, necessitating nutritional supplementation by the vineyard managers. In trying to protect their vines from competition, these managers have unintentionally also prevented mycorrhizal colonization, making the effects of competition from other plants more extreme. By trying to help the vines, we might actually be harming them in the long run. It’s a theme I see all too often in Viticulture.

Data from Moukarzel, et al., 2024 showing a reduction of AMF colonisation, across a range of rootstocks, from Organic management.

A paper looking into mycorrhizal colonisation in organic versus conventional vineyards in New Zealand found a lower percentage of mycorrhizae in the roots from organic blocks than the herbicide blocks across a range of rootstocks, presumably due to the damage to vine roots from undervine tillage in the Organic system (Moukarzel et al., 2024). Don’t get me wrong, tillage is sometimes necessary, but I feel the overreliance on it does more harm than good. Organic growers that want a bare undervine are still living in the “old system.” They’re trying to recreate the visuals of an herbicide managed vineyard, but using a less efficient, and less long lasting tool to achieve it. This is the recipe for very expensive farming, and it is undervine management that pushes most folks who give organics a try back to using herbicide.

Strategies for Raising Resilient Vines

As parents of a young kid in the age of emotional intelligence and "raising resilient kids" we are inundated with parenting advice and the parallels to vineyard management

can be rather funny. For example:

Instead of...	Try...	Viticultural Practices that might help:
My vineyard is too vigorous..	These vines have ample nutrition and water	Undervine cover cropping, water management, nutritional management, pruning system, training system
The fruit from this vineyard is aweful!	Do I just not like Pinot Gris? OR How can we work to support the vines to produce better fruit?	Define what is "lacking," create a game plan to achieve better fruit quality (nutrition, water, cropload, variety, etc), bring in some outside persepectives if you get stuck.
The weeds are taking over!	The weeds add some great biodiversity to my vineyard	Take a deep breath, and assess/remove noxious weed species, identify species that could pose a problem due to nutrient requirements or growth habits, identify the positive impacts of certain "weed" species
The canopy in organic vineyards is so yellow!	Those vines look like they need a snack. I wonder what they need?	Take soil and vine nutrient samples, measure irrigation requirements, review the cover cropping progra

Literature cited

Moukarzel, R., Jones, E. E., Panda, P., Larrouy, J., Ramana, J. V., Guerin-Laguette, A., & Ridgway, H. J. (2024). Vineyard management systems influence arbuscular mycorrhizal fungi recruitment by grapevine rootstocks in New Zealand. Journal of Applied Microbiology, 135(8), lxae211.