Poor soil produce better wines than fertile soil

There are a few reasons bad soil yields higher quality grapes. Grapevines need to be stressed to produce quality fruit. The poor soil encourages the roots to dig deeper for water and other nutrients. As they dig, the roots begin to ramify, which increases the surface area of the roots that comes into contact with the soil. In turn, more nutrients are delivered to the precious clusters of berries. Also, more roots means better regulation of water supply, which is very important during the veraison, or the ripening stages of grape.

On the other hand, fertile soils make it easier for vines to produce grapes which may overproduce. When this happens, the quality of fruit is compromised for quantity.