which ripen slowly and whose grapes are resistant to early autumn frosts. In warmer climates, later fruiting varieties with high yields are grown. To make good wine you need well-ripened grapes, but the maturation process should not be too rapid nor too advanced because this leads to a loss in aroma; thus varieties are chosen with close attention paid to the maturation period. For the vineyards that are situated at the edges of climatic zones, the big problem is inconsistency of climatic conditions during the maturation period.
Excessive dryness or humidity also play a part. The soil plays an essential role in the irrigation of the plant; in spring, during the growing period, it supplies the vines with water and allows any excess rain during maturation to drain away. Gravelly and chalky soils are particularly suited to this, but there are also highly reputable crus that are grown on sandy and even clayey soils. Artificial drainage is sometimes used, and this accounts for the existence of high-quality crus being grown on different types of soil, while neighbouring vineyards, with the same soil type, produce wine of varying quality.
The different types of soil and subsoil can affect the colour, aroma and taste of wines from the same variety and growing in the same climatic conditions. Wines can vary depending on whether the soil is chalky, clayey, sandy or gravelly or a combination of any of these. An increase in the proportion of clay in Graves makes the wine more acidic, more tannic and full bodied and less refined; a white Sauvignon takes on more flowery notes when grown on chalky, gravelly or marly soils. In any case, the vine is not particular about the quality of the soil on which it grows. In fact, poor soil is often a contributory factor in good wines, as the yield is limited and characteristics, such as colour, aroma and taste, are subsequently advanced.