Viticulture
Grafting: why almost every vine is two plants
A European fruiting variety joined to an American root system — the solution to phylloxera, and now used for much else besides.
The short answer
Nearly all commercial vines are two plants joined at a graft union: a scion of the fruiting variety above, and a rootstock of American or hybrid origin below. The scion determines the fruit; the rootstock determines how the vine interacts with the soil.
Overview
This is one of the most consequential facts about modern viticulture and one of the least known outside the trade.
It began as an emergency response to phylloxera and has since become a routine tool for managing soil, water and vigour.
How it works
The mechanism, at the scope it has actually been established.
The graft union is the visible swelling near the base of the trunk. Above it, the plant is Vitis vinifera; below it, an American species or hybrid.
Because the fruiting variety is above the union, grafting does not change what the grape is. A grafted Chardonnay vine produces Chardonnay.
Bench grafting joins scion and rootstock in a nursery before planting, and is how most vines are now produced. Field grafting — grafting a new variety onto an established root system in place — allows a grower to change variety without replanting, and gives a crop within a couple of years rather than four or five.
Graft compatibility is not universal. Some scion–rootstock combinations perform poorly, and rootstock choice interacts with the variety as well as with the site.
The union remains a permanent weak point, mechanically and as a route for trunk disease infection.
Own-rooted vines still exist where phylloxera has not established — much of Chile, parts of Australia, sandy coastal sites, and some island vineyards — and in a few places where growers accept the risk.
What people get wrong
2 widely repeated claims this page corrects.
Oversimplified
“American grapevines are immune to phylloxera, which is why we graft onto them.”
They are tolerant, not immune. American species evolved alongside the insect and survive its feeding on their roots; European vines do not. The insect still lives on them.
Oversimplified
“Chile never had phylloxera, so its vines are the original ungrafted European stock.”
Chile has largely escaped phylloxera and much of its vineyard is ungrafted, which is genuinely unusual. That does not make its vines a preserved nineteenth-century snapshot.
In history
Sources
Sources consulted
- UC Davis Department of Viticulture and Enology — University of California, Davis
- INRAE — French National Research Institute for Agriculture, Food and Environment — INRAE
- Scholarship on the phylloxera epidemic and grafting — Academic history of agriculture
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