beaucoup cailloux

"Cayuse" comes from the French word cailloux meaning "stones." Grapes love 'em. I don't.
Rocky ground is good for grapes for several reasons. First, when the soil is lean, the vine's survival mechanisms tend to direct the limited nutrients to the berry rather than the foliage. The grapes are smaller and the flavors more concentrated and powerful.
Second, the root systems can be deeper and stronger in rocky soil as they dig deep in search of water & nutrients. This makes for a hardier vine.
Rocky soil also ensures good drainage, which is critical for growing good grapes.
Finally, certain types of rock absorb heat from daytime sunshine and then radiate that heat after dark. This warms the ground and can promote the ripening process and help prevent winterkill.
I plan on gathering the rocks in the rows and around the plants as a sort of rock mulch.