Abstract Montepulciano red grape is cultivated in the northern part of the Latium region, primarily for the production of DOC “Colli Etruschi Viterbesi” structured wines for aging. In Mediterranean areas, viticulture is closely influenced by vine water status. In this context, the practice of irrigation may alleviate water-stress-related reductions in plant development to guarantee grape quality, especially in semi-arid areas. The application of on-farm compost in a vineyard may affect grape quality without negative effects, thereby enhancing environmental sustainability. The aim of this work was to investigate the combined effect of irrigation and compost application on the Montepulciano variety in the volcanic environment of Latium region, thereby improving the polyphenol concentrations in the berries. The trial was conducted during three growing seasons (2011-2013). Irrigation was performed according to the protocol proposed by Ojeda and Saurin (2014). The pre-dawn leaf water potential (ψpd) from July to September was measured weekly for maintaining vine water status in the range between −0.4 and −0.6 Mpa. Irrigation (I) and irrigation plus compost application (IC) were compared to a non-irrigated control (C). Berry weight was not influenced by moderate irrigation, whereas titratable acidity and total soluble solids were negatively correlated to the increment of water dropped. The primary finding was a positive influence on polyphenol contents of the grapes at harvest. Best performance was highlighted in 2012 with 263 liter vine−1 of water supplied. Overall, the sustainable use of water and on-farm compost improved Montepulciano grape quality in this volcanic area, thereby enhancing the adaptation of Mediterranean viticulture to climate change conditions.