A superior vineyard site can make organic growing a more realistic goal. A climate that is not too hot and humid will increase your chances of success. If site selection is a non-issue because you already own one, you should attempt to manipulate vineyard layout with your organic aspirations in mind.
Whether you are interested in 10 vines, or 10 acres, clear cultivation of the vineyard floor should be high up on your list of priorities. Relatively level ground is, of course, ideal, but clear cultivation is practiced on rolling terrain and the steep slopes of vineyards in the Mosel River Valley. Where erosion is a threat, the grower needs (a) a plan to prevent it, and (b) a plan to replace lost soil (see Floor Management).
A second consideration for organic vineyard site selection is air drainage. This term refers to the inhibiting effect good air circulation has on fungus and mildew spores and the reduction of humid conditions which help these pests find a toehold among your vines. Obviously, planting vines next to a building, hillside, or tree row which stands perpendicular to prevailing wind should be avoided. On the other hand, a downwind hillock can enhance air flow by creating a slight vacuum effect among the vines.
Vineyard layout parallel, or perpendicular to prevailing winds is less important than simply permitting air to circulate through the fruit zone and the vine canopy. Vineyard management practices can improve on a less than ideal site much more readily than prevailing wind guesswork will permit (see Pest Control).
Other influences on vineyard site selection are not unique to organic growing. Previous site use (e.g. alfalfa production) can raise nematode populations so high that soil fumigation is necessary to make the site practicable for grapes. In this case, the use of fumigant is so expensive that all growers blanch at the thought.
"Hot spots" for Pierce's Disease should certainly be a site selection influence. But the new vector from South America, the Glassy Winged Sharpshooter seems to be willing to go anywhere, so the hot spot concept may rapidly become a thing of the past and all viticultural sites in mild climates now have the potential of developing Pierce's Disease (see Pierce's Disease, Vineyard Pest Management).
A comprehensive paper on site selection by Dr. Tony Wolf, Virginia Tech University, may be accessed on the links pages.
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