The vineyard is made up of one single block adjacent to the village of Saint-Estèphe. Unique in the Médoc, it is completely surrounded by a stone wall. Inside, closest to the château, this "enclos" groups together the most famous plots of Calon. Cabernet Sauvignon is the backbone of Calon Ségur. This grape variety makes up over three-quarters of the blend, and in great years its proportion can be as high as 90%. No great wines can ever be made without constant and meticulous care of the vines. The soils are ploughed in the time-honoured tradition. From spring to autumn, vine canopy management tasks are done by large numbers of vineyard personnel. The crop is picked by hand at perfect ripeness.

Saint-Estephe is located marginally further away from the gravel-bearing waters of the Garonne river, and the soil here is far less stony than that found in the southern part of Haut-Medoc. Instead, a heavy clay base dominates this area, resulting in poorer-draining soils, delayed ripening and higher acidity levels in the wine. These factors mean that Saint-Estephe's blended wine are predominantly made from Merlot, as it performs better on clay soils than Cabernet Sauvignon. Because these wine are often austere and tight in youth, Merlot also serves to soften the palate.