A molding apparatus for manufacturing a wind turbine blade component includes a main mold body (30) and a flexible bladder (38). The main mold body includes a shape defining surface (32) for receiving composite material forming the blade component and a heat reservoir (40) for heating the blade component during curing. The flexible bladder overlays and conforms to the shape of the blade component and is configured to receive heated liquid for heating the blade component during curing. One or both of the main mold body and the flexible bladder is divided into a plurality of zones (58, 66) that are independently controlled by a controller (70) to maintain a generally uniform temperature of the blade component at each zone.