Background and Aims: Springtime root-zone warming activates mobilisation of the root carbohydrate reserves, a critical source of carbon for early canopy and reproductive development in grapevines following winter dormancy. Seasonal variability in soil temperature during spring may result in inconsistent vegetative growth and fruitset with consequences for berry growth and ripening. Methods and Results: We monitored flowering and berry ripening in Shiraz grapevines (Vitis viniferaL.) grown in large temperature-controlled pots. The vines were exposed to a cool, ambient and warm root-zone temperature from budburst to fruitset. Root starch mobilisation after budburst was linearly correlated to the cumulative heat units received by the soil. A warm root-zone temperature also hastened leaf expansion, net positive carbon assimilation, onset of flowering and fruit set, berry enlargement and the onset of veraison. At harvest, berry pH and nitrogen concentration as well as fresh and dry mass were higher for the vines exposed to a warm root-zone while berry acidity was lower. Conclusions: Warm soil temperature in spring stimulated the mobilisation of carbohydrates in the roots and accelerated shoot and reproductive development, resulting in larger berries with lower acidity. Significance of the Study: Because root-zone temperature is an environmental driver of berry size and composition, models predicting yield and berry composition can be fine-tuned to incorporate this critical parameter.