Are own-rooted grapevines superior to grapevines grafted on rootstocks?

Two east side Mokelumne River-Lodi Zinfandel specimens over 100 years old: (left) from Kirschenmann Vineyard planted on its own natural roots; (right) Steacy Vineyard planted on St.George rootstocks.

When wine buffs talk about the great wines of the world, they often talk about terroir, an important term of French origin that entails the natural environmental factors—such as climate, soil, topography, aspect, elevation, latitude, etc.—that have a direct effect on grapevine growth, and ultimately on the taste of wines. While terroir is more than about natural conditions—the hand of man also plays a big part of winegrowing—soil plays a crucial role.

Because the closest part of any plant to the ground is its root system, another hot topic of discussion when it comes to grapevines is rootstocks. That is to say, the rooting habits of specifically chosen rootstock selections that might be favorable to a site's soil, or to meet specific objectives such as drought tolerance, disease and pest resistance, grapevine vigor, canopy growth, a targeted average cluster weight, and a host of other concerns.

When consumers shop for wine, of course, rootstocks are the last thing on their mind. All the same, rootstocks are an important subject for farmers or vineyard owners, whose job is to deliver high quality grapes to wineries or winemakers.

Vintage illustration of the effects of the grapevine-debilitating root louse known as phylloxera.

For well over a century, rootstocks have also been a burning question throughout the wine industry, all around the world.

Reason: In the latter half of the nineteenth century, the microscopic root louse infamously known as phylloxera killed off vineyards almost everywhere else in California and most major wine regions around the world. No country was spared. This catastrophic event necessitated the grafting of phylloxera-resistant rootstocks, primarily derived from native American species (Vitis labrusca). 

Phylloxera, however, does not thrive in sandy soils (for deeper reading, see our post on Impact of phylloxera on Lodi’s vaunted old vines and their natural defenses).

For this reason, the situation in Lodi has always been different from anywhere else in California; mostly because pioneering nineteenth century growers always chose to plant in farmlands surrounding the City of Lodi marked by extremely deep, and rich, alluvium with a high sand content, and no hardpan even at depths below 50 feet. Why? Because that’s where grapevines—particularly varieties such as Zinfandel, Cinsaut, Carignan and Flame Tokay—seemed to set healthy, deep rooting systems sooner, and produce the highest quality grapes. A simple case of observation and conclusion.

Below an old vine Mokelumne River-Lodi Zinfandel plant, ultra-fine and fluffy, high vigor sandy loam soil in the Tokay series; an alluvium going down 50 to 100-ft. before hitting a hardpan.

Because sandy soils have always been inhospitable to phylloxera, thousands of acres of Vitis vinifera (i.e., belonging to the European family of wine grapes) planted in what is now known as the Mokelumne River AVA of Lodi before and after 1900 have been able to survive ungrafted, producing healthy yields on the strength of their own natural or "wild" roots.

The phenomenon of own-rooted Zinfandel plantings in Lodi is closely tied to the soil series defining the Mokelumne River appellation: Tokay fine sandy loam. Lodi winemaker/grower Mike McCay talks about pulling out a 100-year-old plant while digging a pit in one of his vineyards, back in 2015:

When we pulled out that vine we found that there wasn't really a root system near the surface. Instead, there was a taproot that was 2 inches wide at about 5 feet below the ground, and still 2 inches wide at 25 feet below, which was about where we stopped digging. At that point there were a couple of feeder roots, but obviously the taproot was going down much deeper, which is probably where we would've found a more extensive root system. 

Taproot of Zinfandel plant over 100 years old dug out from a Mokelumne River-Lodi vineyard.

I'll argue that Zinfandel plantings over 100 years old in Lodi tap into whatever water sources they can find, sending their taproot through all the permutations in that sandy soil, including a few layers of limestone we found in our vineyard. I still don't know exactly how far down the roots go, but I can tell you that in a typical growing season we'll water just once, and the vines remain perfectly healthy and productive all the way through. This is completely different from my trellised vineyards on drip systems, where roots go down only about 6 feet, and you have to constantly monitor their intake to keep things going.

Some examples of own-rooted Zinfandel vineyards that have gained notoriety over recent years through single-vineyard bottlings include 

• Marian's Vineyard (St. Amant Winery), planted in 1901
• Lizzy James Vineyard (Harney Lane Winery), 1904
• Royal Tee Vineyard (Jessie's Grove Winery), 1889
• Kirschenmann Vineyard (Turley Wine Cellars, Sandlands and Precedent), 1915
• Stampede Vineyard (Perlegos Family, Fields Family, Maître de Chai, Christopher Cellars, Haarmeyer), 19202-1940s
• Scottsdale Vineyard (Harney Lane Winery), early 1900s
• Charlie Lewis Vineyard (LangeTwins Family Winery), 1903
• Katushas’ Vineyard (Bedrock Wine Co.), 1915
• Mohr-Fry Ranches (multiple blocks sold to several wineries, planted in the early 1940s)
• Fathom Vineyard (Mettler Family Vineyards), 1920s
• Faith Vineyard (Monte Rio Cellars), 1918
• ZinStar Vineyard (The Lucas Winery), 1936
• Dogtown Vineyard (Turley Wine Cellars), 1944

20-ft. sandpit dug under Bechthold Vineyard Cinsaut (ancient own-rooted vines planted in 1886) demonstrating the consistency of the fine sandy loam soil defining Lodi's Mokelumne River appellation, allowing ungrafted vines to thrive for as long as their fruit is in demand.

Other own-rooted, old or ancient vine Lodi vineyards planted to other grape varieties include 

• Bechthold Vineyard (Cinsaut planted in 1886) 
• Rauser Vineyard (Carignan, 1909)
• Spenker Ranch (Carignan, 1900) 
• Mule Plane Vineyard (Carignan, late 1920s)
• Manassero Vineyard (Grenache from 1940s and Carignan from 1950s)
• Church Block (Carignan/Petite Sirah/Alicante Bouschet mix, late 1930s)
• Somers Vineyard (Mission, 1970s)
• Chandler Vineyard (Flame Tokay, late 1890s)
• Old School Vineyard (Flame Tokay, 1906)

Typically bushy foliage of St. George rootstock (i.e., Vitis rupestris) cultivated in a Clements-Hills-Lodi vineyard originally planted with own-rooted Zinfandel, with  "dead" spots now replaced with grafted vines.

St. George rootstock

By far the most popular rootstock selected for replantings of Zinfandel throughout California before and after the turn of the last century was St. George, a variety of Vitis rupestris. 

Because of the constant, looming threat of phylloxera, most of California’s old vine Zinfandel growths are grafted on one kind of rootstock selection or another, Lodi being the graphic exception. The fact that ungrafted Zinfandel is so naturally adapted to Lodi’s terroir is, undoubtedly, the primary reason why there is more Zinfandel grown in Lodi (over 40%) than anywhere else in California.

Which brings up the question: Is own-rooted Vitis vinifera superior to grafted Vitis vinifera? There is plenty of evidence supporting the advantages of selecting rootstocks for specific sites and performance expectations.

Certified organic and Historic Vineyard sign in The Lucas Winery's ZinStar Vineyard; own-rooted west side Lodi Zinfandel planted in 1936.

Although Vitis rupestris is of American origin, the rootstock first became popular in the area around the Southern French town of Saint-Georges-d’Orques, hence its name. After the usage of St. George rootstock was introduced to California during the 1890s, it quickly became popular among California Zinfandel growers, especially in Sonoma County and Napa Valley, because it provided an exceptionally deep rooting system in poor soils, shallow hillsides, and areas prone to droughts. 

Interestingly, Vitis rupestris is not actually a grapevine; it is a grape bush that once grew wild on prairies, and in gravelly creeks and sand bars all over central U.S. from Texas to West Virginia. It is now listed as an endangered plant species.

Image from 1905 study showing rootstock growth of three different species, left to right: Riparia Gloire de Montpelier (V. riparia Michaux), V. riparia x V. rupestris cv. 3309C, and Rupestris du Lot (V. rupestris Scheele). Guillon; reproduced with the permission of Masson Publishers/Dunod, Paris.

St. George makes an excellent rootstock for old vines because it is known for its extensive root system and reduced fruit set—ideal for varieties such as Zinfandel—although it is also susceptible to nematodes, which can debilitate vigor and yields, especially in moist soil conditions. 

Better known examples of old vine Lodi vineyards grafted on St. George include

• Steacy Ranch (Turley Wine Cellars), first planted in 1907
• Rous Vineyard (Ironstone Vineyards), 1909
• Wegat Vineyard (Maley Bros. Lodi Native), 1958

To be clear, though, here in Lodi grapevines with proven track records of long term health and productivity are grown on both natural and St. George rootstocks. All of the region’s old vine plantings have been observed to ripen early with moderate yields, leading to the conclusion that the prevailing factor for high performing old vines in this region has not been choice of rootstocks, but rather the region's combination of sandy soil composition and mild Mediterranean climate naturally conducive to high vigor Mediterranean grapes (such as Zinfandel, Carignan, Cinsaut, and others).

Dropped Zinfandel during harvest in 100-year-old riverside Clements Hills-Lodi vineyard planted on its own roots.

Wines from own-rooted vs. grafted vines

Which brings up the final burning question: Do own-rooted vines produce wines that are different or better, in terms of sensory qualities, from grafted vines?

The simple answer: Probably not. The evidence that we have, based upon all of our studies of Lodi wines made from old vines, seems to indicate that the advantage of being own-rooted is not in itself a deciding factor when it comes sensory qualities. Excellent wines are made from old vines that are both own-rooted and grafted.

If anything, sensory variations among, say, Lodi Zinfandels have more to do with

1. Vine age (blocks planted over 100 years old tend to produce more layered and delineated wines than blocks just over 50 years old).

2. Location (it is well known that Zinfandels grown on the east side of Lodi are more floral and red fruited than Zinfandels on the west side, which are earthier and more black-fruited).

In other words, when it comes to both quality and sensory profiles, terroir (i.e., site-specific location) and vine age trump rootstocks every time—at least in Lodi.

Own-rooted, late 1920s Alicante Bouschet in Lodi's Mohr-Fry Ranches in a 5-acre vineyard torn out in 2012, then replanted as trellised vines on grafted rootstocks two years later.