The roots of grape vines are in general deeper and less dense the roots of most plants. Viticulturalists look at the growth of grape vines above ground for a rough determination of the spread and depth of the root system; older, vigorously growing vines usually have wider and deeper roots. Well-developed root systems yield more grapes with better juice. Differences in the mass, depth and spread of roots depend a great deal on the variety of grape, type of soil and the weather.
Viticulturalists at the University of California-Davis say studies of grape roots show that about 60 percent of roots grow in the top 2 feet of soil. The remaining 40 percent of roots grow deeper with depths reported as deep as 20 feet. Layers of gravel, clay or large stones can cause a patchy distribution of roots as they seek the past of least resistance. Lower water tables cause roots to grow deeper. Since grape roots vary according to their variety, soil and climate, Australian viticulturalists recommend physically digging down to see how deep the roots are growing.
UC-Davis viticulturalists say a study concluding that lateral roots can spread up to 32 feet from the trunk is likely accurate. A. S. Colby of the University of Illinois, writing in the Journal of the American Society of Horticultural Science, says grape vines should be planted no closer than 10 to 12 feet apart to accommodate lateral root spread.
The most precise study found by UC-Davis viticulturalists reported that 15 percent of the total biomass of a grape vine, in the form of roots, was located between 4 to 5 feet from the trunk. Another study concluded that soil with a coarse texture has the lowest root density; fine-textured soils have the highest root density.
Vinifera vs. Lubrusca
A.S. Colby writes that there are differences in the root systems of the two main varieties of grape vines, Vitis vinifera and Vitis lubrusca. Vitis vinifera, the vines native to Europe and central Asia, are associated with wine and culinary uses. Vitis lubrusca, including the well-known concord variety, is native to the eastern U.S. and Canada and is used for grape juice and making jams and jellies. Studies show that the roots of Vitis vinifera grow deeper than the roots of Vitis lubruska.