Wine Arcana

Concept

Grafting

Grafting joins living parts of two plants so that they grow as one vine. The scion supplies the fruit-bearing shoots of the desired grape variety; the rootstock supplies the roots. This combination lets growers retain a variety such as Cabernet Sauvignon while choosing a root system suited to vineyard pests and growing conditions.

The scion retains its varietal identity while the rootstock influences its growth. Breeding a cross produces genetically new offspring; grafting connects existing plants.

Making the union

Successful joining requires contact between the partners' vascular cambium, the thin growth tissue between the wood and inner bark. Healing tissue forms at the cut surfaces and connects the graft. The union must develop sufficiently to support the growing scion.1. Justin Scheiner and Andrew King, Propagating Grapevines, Texas A&M AgriLife Extension, 2019, grafting and field-grafting sections.

Nurseries commonly bench-graft dormant pieces of scion and rootstock, then allow the union to heal and the rootstock to form roots. Field grafting joins new scion material to an established vine. Growers can use this second method, also called topworking, to change the fruiting variety while retaining an existing root system.

Why resistant roots matter

Phylloxera is a small insect that feeds on grapevine roots. On susceptible vines, feeding damage and secondary infection can destroy parts of the root system, reducing growth and yield. Vitis vinifera, the species containing most familiar wine grapes, is vulnerable. Rootstocks derived from resistant American grape species supplied a practical response to the vineyard losses caused by the pest.

Resistance protects the vine while phylloxera may remain present. University of California pest-management guidance notes that resistant young rootstocks can still support small populations and suffer stunting in heavily infested replant sites. Its warning about the historical failure of AXR#1 in California also shows why protection must be evaluated for the particular rootstock and pest population.2. University of California Statewide Integrated Pest Management Program, “Grape Phylloxera,” damage and cultural-control sections, accessed 14 September 2026.

Other root pests pose different problems. Plant-parasitic nematodes are tiny roundworms, and a rootstock resistant to one species may be susceptible to another. Some nematodes transmit viruses as they feed. Resistance to the nematode does not necessarily prevent virus transmission, because even brief feeding can transfer the pathogen.3. University of California Statewide Integrated Pest Management Program, “Nematodes,” rootstocks and virus-vector sections, accessed 14 September 2026.

Matching roots to the site

Rootstocks also differ in drought tolerance, vigour, and adaptation to soil conditions. Their performance depends on the scion and the vineyard environment. A root system supporting vigorous growth may be useful where the soil limits the vine, but require different irrigation and canopy management on a more generous site.

A Coonawarra trial summarized by viticulturist Nick Dry illustrates the interaction. The drought-tolerant rootstocks 1103 Paulsen and 140 Ruggeri produced vigorous vines, and the trial raised questions about managing that growth during wetter conditions. Applying the same management across rootstocks can influence their apparent performance.4. Nick Dry, rootstock-selection workshop presentation, 2022, Coonawarra trial summary and 1103 Paulsen/140 Ruggeri observations. The practical choice must consider water supply and the intended vine size alongside pest resistance.

Plant health and establishment

A healthy graft also depends on the planting material. Propagation can carry pathogens already inside the plant tissues. Nursery certification programmes use testing and inspection to reduce this risk; the scope of testing matters to what that certification establishes. Oregon State University's vineyard establishment guidance emphasizes certified sources for both cultivars and rootstocks and specifically identifies leafroll, red blotch, and fanleaf among the viruses of concern.5. Oregon State University Extension Service, Establishing a vineyard in Oregon: A quick-start resource guide, plant-material section, accessed 14 September 2026.

A suitable rootstock can offer durable protection against a soil pest while an infected scion introduces a different problem.

Sources